First of all, in the context of science, you should never speak of evolution as a “theory.” There is no theory about whether or not evolution happens. It is a fact.
Scientists have, however, developed tested theories about how evolution happens. Although several proposed and tested processes or mechanisms exist, the most prominent and most studied, talked about, and debated, is Charles Darwin’s idea that the choices of nature guide these changes. The fame and importance of his idea, natural selection, has eclipsed the very real existence of other ways that populations can change over time.
Evolution in the biological sense does not occur in individuals, and the kind of evolution we’re talking about here isn’t about life’s origins. Evolution must happen at least at the populationlevel. In other words, it takes place in a group of existing organisms, members of the same species, often in a defined geographical area.
We never speak of individuals evolving in the biological sense. The population, a group of individuals of the same species, is the smallest unit of life that evolves.
To get to the bottom of what happens when a population changes over time, we must examine what’s happening to the gene combinations of the individuals in that population. The most precise way to talk about evolution in the biological sense is to define it as “a change in the allele frequency of a population over time.” A gene, which contains the code for a protein, can occur in different forms, or alleles. These different versions can mean that the trait associated with that protein can differ among individuals. Thanks to mutations, a gene for a trait can exist in a population in these different forms. It’s like having slightly different recipes for making the same cake, each producing a different version of the cake, except in this case, the “cake” is a protein.
Natural selection: One way evolution happens
Charles Darwin, a smart, thoughtful, observant man. Via Wikimedia.
Charles Darwin, who didn’t know anything about alleles or even genes (so now you know more than he did on that score), understood from his work and observations that nature makes certain choices, and that often, what nature chooses in specific individuals turns up again in the individuals’ offspring. He realized that these characteristics that nature was choosing must pass to some offspring. This notion of heredity–that a feature encoded in the genes can be transmitted to your children–is inherent now in the theory of natural selection and a natural one for most people to accept. In science, an observable or measurable feature or characteristic is called a phenotype, and the genes that are the code for it are called its genotype. The color of my eyes (brown) is a phenotype, and the alleles of the eye color genes I have are the genotype.
What is nature selecting any individual in a population to do? In the theory of natural selection, nature chooses individuals that fit best into the current environment to pass along their “good-fit” genes, either through reproduction or indirectly through supporting the reproducer. Nature chooses organisms to survive and pass along those good-fit genes, so they have greater fitness.
Fitness is an evolutionary concept related to an organism’s reproductive success, either directly (as a parent) or indirectly (say, as an aunt or cousin). It is measured technically based on the proportion of an individual’s alleles that are represented in the next generation. When we talk about “fitness” and “the fittest,” remember that fittest does not mean strong. It relates more to a literal fit, like a square peg in a square hole, or a red dot against a red background. It doesn’t matter if the peg or dot is strong, just whether or not it fits its environment.
One final consideration before we move onto a synthesis of these ideas about differences, heredity, and reproduction: What would happen if the population were uniformly the same genetically for a trait? Well, when the environment changed, nature would have no choice to make. Without a choice, natural selection cannot happen–there is nothing to select. And the choice has to exist already; it does not typically happen in response to a need that the environment dictates. Usually, the ultimate origin for genetic variation–which underlies this choice–is mutation, or a change in a DNA coding sequence, the instructions for building a protein.
Don’t make the mistake of saying that an organism adapts by mutating in response to the environment. The mutations (the variation) must already be present for nature to make a choice based on the existing environment.
The Modern Synthesis
Darwin presented his ideas about nature’s choices in an environmental context, he did so in a book with a very long title that begins, On the Origin of Species by Means of Natural Selection.Darwinknew his audience and laid out his argument clearly and well, with one stumbling block: How did all that heredity stuff actually work?
We now know–thanks to a meticulous scientist named Gregor Mendel (who also was a monk), our understanding of reproductive cell division, and modern genetics–exactly how it all works. Our traits–whether winners or losers in the fitness Olympics–have genes that determine them. These genes exist in us in pairs, and these pairs separate during division of our reproductive cells so that our offspring receive one member or the other of the pair. When this gene meets its coding partner from the other parent’s cell at fertilization, a new gene pair arises. This pairing may produce a similar outcome to one of the parents or be a novel combination that yields some new version of a trait. But this separating and pairing is how nature keeps things mixed up, setting up choices for selection.
With a growing understanding in the twentieth century of genetics and its role in evolution by means of natural selection, a great evolutionary biologist named Ernst Mayr (1904–2005) guided a meshing of genetics and evolution (along with other brilliant scientists including Theodosius Dobzhansky, George Simpson, and R.A. Fisher) into what is called The Modern Synthesis. This work encapsulates (dare I say, “synthesizes?”) concisely and beautifully the tenets of natural selection in the context of basic genetic inheritance. As part of his work, Mayr distilled Darwin’s ideas into a series of facts and inferences.
Facts and Inferences
Mayr’s distillation consists of five facts and three inferences, or conclusions, to draw from those facts.
The first fact is that populations have the potential to increase exponentially. A quick look at any graph of human population growth illustrates that we, as a species, appear to be recognizing that potential. For a less successful example, consider the sea turtle. You may have seen the videos of the little turtle hatchlings valiantly flippering their way across the sand to the sea, cheered on by the conservation-minded humans who tended their nests. What the cameras usually don’t show is that the vast majority of these turtle offspring will not live to reproduce. The potential for exponential growth is there, based on number of offspring produced, but…it doesn’t happen.
The second fact is that not all offspring reproduce, and many populations are stable in size. See “sea turtles,” above.
The third fact is that resources are limited. And that leads us to our first conclusion, or inference: there is a struggle among organisms for nutrition, water, habitat, mates, parental attention…the various necessities of survival, depending on the species. The large number of offspring, most of which ultimately don’t survive to reproduce, must compete, or struggle, for the limited resources.
Fact four is that individuals differ from one another. Look around. Even bacteria of the same strain have their differences, with some more able than others to with stand an antibiotic onslaught. Look at a crowd of people. They’re all different in hundreds of ways.
Fact five is that much about us that is different lies in our genes–it is inheritable. Heredity undeniably exists and underlies a lot of our variation.
So we have five facts. Now for the three inferences:
First, there is that struggle for survival, thanks to so many offspring and limited resources. See “sea turtle,” again.
Second, different traits will be passed on differentially. Put another way: Winner traits are more likely to be passed on.
And that takes us to our final conclusion: if enough of these “winner” traits are passed to enough individuals in a population, they will accumulate in that population and change its makeup. In other words, the population will change over time. It will be adapted to its environment. It will evolve.
Darwin presented his idea of natural selection, he knew he had an audience to win over. He pointed out that people select features of organisms all the time and breed them to have those features. Darwin himself was fond of breeding pigeons with a great deal of pigeony variety. He noted that unless the pigeons already possessed traits for us to choose, we not would have that choice to make. But we do have choices. We make super-woolly sheep, dachshunds, and heirloom tomatoes simply by selecting from the variation nature provides and breeding those organisms to make more with those traits. We change the population over time.
Darwin called this process of human-directed evolution artificial selection. It made great sense for Darwinbecause it helped his reader get on board. If people could make these kinds of choices and wreak these kinds of changes, why not nature? In the process,
Darwin also described this second way evolution can happen: human-directed evolution. We’re awash in it today, from our accidental development of antibiotic-resistant bacteria to wheat that resists devastating rust.
Genetic drift: fixed or lost
What about traits that have no effect either way, that are just there? One possible example in us might be attached earlobes. Good? Bad? Ugly? Well…they don’t appear to have much to do with whether or not we reproduce. They’re just there.
When a trait leaves nature so apparently disinterested, the alleles underlying it don’t experience selection. Instead, they drift in one direction or another, to extinction or 100 percent frequency. When an allele drifts to disappearance, we say that it is lost from the population. When it drifts to 100 percent presence, we say that it has become fixed. This process of evolution by genetic drift reduces variation in a population. Eventually, everyone will have it, or no one will.
Gene flow: genes in, genes out
Another way for a population to change over time is for it to experience a new infusion of genes or to lose a lot of them. This process of gene flow into or out of the population occurs because of migration in or out. Either of these events can change the allele frequency in a population, and that means that gene flow is another was that evolution can happen.
If gene flow happens between two different species, as can occur more with plants, then not only has the population changed significantly, but the new hybrid that results could be a whole new species. How do you think we get those tangelos?
Horizontal gene transfer
One interesting mechanism of evolution is horizontal gene transfer. When we think of passing along genes, we usually envision a vertical transfer through generations, from parent to offspring. But what if you could just walk up to a person and hand over some of your genes to them, genes that they incorporate into their own genome in each of their cells?
Of course, we don’t really do that–at least, not much, not yet–but microbes do this kind of thing all the time. Viruses that hijack a cell’s genome to reproduce can accidentally leave behind a bit of gene and voila! It’s a gene change. Bacteria can reach out to other living bacteria and transfer genetic material to them, possibly altering the traits of the population.
Sometimes, events happen at a large scale that have huge and rapid effects on the overall makeup of a population. These big changes mark some of the turning points in the evolutionary history of many species.
The word bottleneck pretty much says it all. Something happens over time to reduce the population so much that only a relatively few individuals survive. A bottleneck of this sort reduces the variability of a population. These events can be natural–such as those resulting from natural disasters–or they can be human induced, such as species bottlenecks we’ve induced through overhunting or habitat reduction.
Founder effect: starting small
Sometimes, the genes flow out of a population. This flow occurs when individuals leave and migrate elsewhere. They take their genes with them (obviously), and the populations they found will initially carry only those genes. Whatever they had with them genetically when they founded the population can affect that population. If there’s a gene that gives everyone a deadly reaction to barbiturates, that population will have a higher-than-usual frequency of people with that response, thanks to this founder effect.
Gene flow leads to two key points to make about evolution: First, a population carries only the genes it inherits and generally acquires new versions through mutation or gene flow. Second, that gene for lethal susceptibility to a drug would be meaningless in a natural selection context as long as the environment didn’t include exposure to that drug. The take-home message is this: What’s OK for one environment may or may not be fit for another environment. The nature of Nature is change, and Nature offers no guarantees.
Hardy-Weinberg: when evolution is absent
With all of these possible mechanisms for evolution under their belts, scientists needed a way to measure whether or not the frequency of specific alleles was changing over time in a given population or staying in equilibrium. Not an easy job. They found–“they” being G. H. Hardy and Wilhelm Weinberg–that the best way to measure this was to predict what the outcome would be if there were no change in allele frequencies. In other words, to predict that from generation to generation, allele frequencies would simply stay in equilibrium. If measurements over time yielded changing frequencies, then the implication would be that evolution has happened.
Defining “Not Evolving”
So what does it mean to not evolve? There are some basic scenarios that must exist for a population not to be experiencing a change in allele frequency, i.e., no evolution. If there is a change, then one of the items in the list below must be false:
·Very large population (genetic drift can be a strong evolutionary mechanism in small populations)
·No migrations (in other words, no gene flow)
·No net mutations (no new variation introduced)
·Random mating (directed mating is one way nature selects organisms)
·No natural selection
In other words, a population that is not evolving is experiencing a complete absence of evolutionary processes. If any one of these is absent from a given population, then evolution is occurring and allele frequencies from generation to generation won’t be in equilibrium.
Arguably the most famous of the egg-laying monotremes, the improbable- seeming platypus. License.
One of the best examples of the influences of environmental pressures is what happens in similar environments a world apart. Before the modern-day groupings of mammals arose, the continent of
Australiaseparated from the rest of the world’s land masses, taking the proto-mammals that lived there with it. Over the ensuing millennia, these proto-mammals in Australiaevolved into the native species we see today on that continent, all marsupialsor monotremes.
Among mammals, there’s a division among those that lay eggs (monotremes), those that do most gestating in a pouch rather than a uterus (marsupials), and eutherians, which use a uterus for gestation (placental mammals).
Elsewhere in the world, most mammals developed from a common eutherian ancestor and, where marsupials still persisted, probably outcompeted them. In spite of this lengthy separation and different ancestry, however, for many of the examples of placental mammals, Australiahas a similar marsupial match. There’s the marsupial rodent that is like the rat. The marsupial wolf that is like the placental wolf. There’s even a marsupial anteater to match the placental one.
How did that happen an ocean apart with no gene flow? The answer is natural selection. The environment that made an organism with anteater characteristics best fit in South America was similar to the environment that made those characteristics a good fit in
Australia. Ditto the rats, ditto the wolf.
When similar environments result in unrelated organisms having similar characteristics, we call that process convergent evolution. It’s natural selection in relatively unrelated species in parallel. In both regions, nature uses the same set of environmental features to mold organisms into the best fit.
Note: This explanation of evolution and how it happens is not intended to be comprehensive or detailed or to include all possible mechanisms of evolution. It is simply an overview. In addition, it does not address epigenetics, which will be the subject of a different explainer.
The four basic categories of molecules for building life are carbohydrates, lipids, proteins, and nucleic acids.
Carbohydrates serve many purposes, from energy to structure to chemical communication, as monomers or polymers.
Lipids, which are hydrophobic, also have different purposes, including energy storage, structure, and signaling.
Proteins, made of amino acids in up to four structural levels, are involved in just about every process of life.
The nucleic acids DNA and RNA consist of four nucleotide building blocks, and each has different purposes.
The longer version
Life is so diverse and unwieldy, it may surprise you to learn that we can break it down into four basic categories of molecules. Possibly even more implausible is the fact that two of these categories of large molecules themselves break down into a surprisingly small number of building blocks. The proteins that make up all of the living things on this planet and ensure their appropriate structure and smooth function consist of only 20 different kinds of building blocks. Nucleic acids, specifically DNA, are even more basic: only four different kinds of molecules provide the materials to build the countless different genetic codes that translate into all the different walking, swimming, crawling, oozing, and/or photosynthesizing organisms that populate the third rock from the Sun.
Big Molecules with Small Building Blocks
The functional groups, assembled into building blocks on backbones of carbon atoms, can be bonded together to yield large molecules that we classify into four basic categories. These molecules, in many different permutations, are the basis for the diversity that we see among living things. They can consist of thousands of atoms, but only a handful of different kinds of atoms form them. It’s like building apartment buildings using a small selection of different materials: bricks, mortar, iron, glass, and wood. Arranged in different ways, these few materials can yield a huge variety of structures.
We encountered functional groups and the SPHONC in Chapter 3. These components form the four categories of molecules of life. These Big Four biological molecules are carbohydrates, lipids, proteins, and nucleic acids. They can have many roles, from giving an organism structure to being involved in one of the millions of processes of living. Let’s meet each category individually and discover the basic roles of each in the structure and function of life.
You have met carbohydrates before, whether you know it or not. We refer to them casually as “sugars,” molecules made of carbon, hydrogen, and oxygen. A sugar molecule has a carbon backbone, usually five or six carbons in the ones we’ll discuss here, but it can be as few as three. Sugar molecules can link together in pairs or in chains or branching “trees,” either for structure or energy storage.
When you look on a nutrition label, you’ll see reference to “sugars.” That term includes carbohydrates that provide energy, which we get from breaking the chemical bonds in a sugar called glucose. The “sugars” on a nutrition label also include those that give structure to a plant, which we call fiber. Both are important nutrients for people.
Sugars serve many purposes. They give crunch to the cell walls of a plant or the exoskeleton of a beetle and chemical energy to the marathon runner. When attached to other molecules, like proteins or fats, they aid in communication between cells. But before we get any further into their uses, let’s talk structure.
The sugars we encounter most in basic biology have their five or six carbons linked together in a ring. There’s no need to dive deep into organic chemistry, but there are a couple of essential things to know to interpret the standard representations of these molecules.
Check out the sugars depicted in the figure. The top-left molecule, glucose, has six carbons, which have been numbered. The sugar to its right is the same glucose, with all but one “C” removed. The other five carbons are still there but are inferred using the conventions of organic chemistry: Anywhere there is a corner, there’s a carbon unless otherwise indicated. It might be a good exercise for you to add in a “C” over each corner so that you gain a good understanding of this convention. You should end up adding in five carbon symbols; the sixth is already given because that is conventionally included when it occurs outside of the ring.
On the left is a glucose with all of its carbons indicated. They’re also numbered, which is important to understand now for information that comes later. On the right is the same molecule, glucose, without the carbons indicated (except for the sixth one). Wherever there is a corner, there is a carbon, unless otherwise indicated (as with the oxygen). On the bottom left is ribose, the sugar found in RNA. The sugar on the bottom right is deoxyribose. Note that at carbon 2 (*), the ribose and deoxyribose differ by a single oxygen.
The lower left sugar in the figure is a ribose. In this depiction, the carbons, except the one outside of the ring, have not been drawn in, and they are not numbered. This is the standard way sugars are presented in texts. Can you tell how many carbons there are in this sugar? Count the corners and don’t forget the one that’s already indicated!
If you said “five,” you are right. Ribose is a pentose (pent = five) and happens to be the sugar present in ribonucleic acid, or RNA. Think to yourself what the sugar might be in deoxyribonucleic acid, or DNA. If you thought, deoxyribose, you’d be right.
The fourth sugar given in the figure is a deoxyribose. In organic chemistry, it’s not enough to know that corners indicate carbons. Each carbon also has a specific number, which becomes important in discussions of nucleic acids. Luckily, we get to keep our carbon counting pretty simple in basic biology. To count carbons, you start with the carbon to the right of the non-carbon corner of the molecule. The deoxyribose or ribose always looks to me like a little cupcake with a cherry on top. The “cherry” is an oxygen. To the right of that oxygen, we start counting carbons, so that corner to the right of the “cherry” is the first carbon. Now, keep counting. Here’s a little test: What is hanging down from carbon 2 of the deoxyribose?
If you said a hydrogen (H), you are right! Now, compare the deoxyribose to the ribose. Do you see the difference in what hangs off of the carbon 2 of each sugar? You’ll see that the carbon 2 of ribose has an –OH, rather than an H. The reason the deoxyribose is called that is because the O on the second carbon of the ribose has been removed, leaving a “deoxyed” ribose. This tiny distinction between the sugars used in DNA and RNA is significant enough in biology that we use it to distinguish the two nucleic acids.
In fact, these subtle differences in sugars mean big differences for many biological molecules. Below, you’ll find a couple of ways that apparently small changes in a sugar molecule can mean big changes in what it does. These little changes make the difference between a delicious sugar cookie and the crunchy exoskeleton of a dung beetle.
Sugar and Fuel
A marathon runner keeps fuel on hand in the form of “carbs,” or sugars. These fuels provide the marathoner’s straining body with the energy it needs to keep the muscles pumping. When we take in sugar like this, it often comes in the form of glucose molecules attached together in a polymer called starch. We are especially equipped to start breaking off individual glucose molecules the minute we start chewing on a starch.
Double X Extra: A monomer is a building block (mono = one) and a polymer is a chain of monomers. With a few dozen monomers or building blocks, we get millions of different polymers. That may sound nutty until you think of the infinity of values that can be built using only the numbers 0 through 9 as building blocks or the intricate programming that is done using only a binary code of zeros and ones in different combinations.
Our bodies then can rapidly take the single molecules, or monomers, into cells and crack open the chemical bonds to transform the energy for use. The bonds of a sugar are packed with chemical energy that we capture to build a different kind of energy-containing molecule that our muscles access easily. Most species rely on this process of capturing energy from sugars and transforming it for specific purposes.
Polysaccharides: Fuel and Form
Plants use the Sun’s energy to make their own glucose, and starch is actually a plant’s way of storing up that sugar. Potatoes, for example, are quite good at packing away tons of glucose molecules and are known to dieticians as a “starchy” vegetable. The glucose molecules in starch are packed fairly closely together. A string of sugar molecules bonded together through dehydration synthesis, as they are in starch, is a polymer called a polysaccharide (poly = many; saccharide = sugar). When the monomers of the polysaccharide are released, as when our bodies break them up, the reaction that releases them is called hydrolysis.
Double X Extra: The specific reaction that hooks one monomer to another in a covalent bond is called dehydration synthesis because in making the bond–synthesizing the larger molecule–a molecule of water is removed (dehydration). The reverse is hydrolysis (hydro = water; lysis = breaking), which breaks the covalent bond by the addition of a molecule of water.
Although plants make their own glucose and animals acquire it by eating the plants, animals can also package away the glucose they eat for later use. Animals, including humans, store glucose in a polysaccharide called glycogen, which is more branched than starch. In us, we build this energy reserve primarily in the liver and access it when our glucose levels drop.
Whether starch or glycogen, the glucose molecules that are stored are bonded together so that all of the molecules are oriented the same way. If you view the sixth carbon of the glucose to be a “carbon flag,” you’ll see in the figure that all of the glucose molecules in starch are oriented with their carbon flags on the upper left.
The orientation of monomers of glucose in polysaccharides can make a big difference in the use of the polymer. The glucoses in the molecule on the top are all oriented “up” and form starch. The glucoses in the molecule on the bottom alternate orientation to form cellulose, which is quite different in its function from starch.
Storing up sugars for fuel and using them as fuel isn’t the end of the uses of sugar. In fact, sugars serve as structural molecules in a huge variety of organisms, including fungi, bacteria, plants, and insects.
The primary structural role of a sugar is as a component of the cell wall, giving the organism support against gravity. In plants, the familiar old glucose molecule serves as one building block of the plant cell wall, but with a catch: The molecules are oriented in an alternating up-down fashion. The resulting structural sugar is called cellulose.
That simple difference in orientation means the difference between a polysaccharide as fuel for us and a polysaccharide as structure. Insects take it step further with the polysaccharide that makes up their exoskeleton, or outer shell. Once again, the building block is glucose, arranged as it is in cellulose, in an alternating conformation. But in insects, each glucose has a little extra added on, a chemical group called an N-acetyl group. This addition of a single functional group alters the use of cellulose and turns it into a structural molecule that gives bugs that special crunchy sound when you accidentally…ahem…step on them.
These variations on the simple theme of a basic carbon-ring-as-building-block occur again and again in biological systems. In addition to serving roles in structure and as fuel, sugars also play a role in function. The attachment of subtly different sugar molecules to a protein or a lipid is one way cells communicate chemically with one another in refined, regulated interactions. It’s as though the cells talk with each other using a specialized, sugar-based vocabulary. Typically, cells display these sugary messages to the outside world, making them available to other cells that can recognize the molecular language.
Lipids: The Fatty Trifecta
Starch makes for good, accessible fuel, something that we immediately attack chemically and break up for quick energy. But fats are energy that we are supposed to bank away for a good long time and break out in times of deprivation. Like sugars, fats serve several purposes, including as a dense source of energy and as a universal structural component of cell membranes everywhere.
Fats: the Good, the Bad, the Neutral
Turn again to a nutrition label, and you’ll see a few references to fats, also known as lipids. (Fats are slightly less confusing that sugars in that they have only two names.) The label may break down fats into categories, including trans fats, saturated fats, unsaturated fats, and cholesterol. You may have learned that trans fats are “bad” and that there is good cholesterol and bad cholesterol, but what does it all mean?
Let’s start with what we mean when we say saturated fat. The question is, saturated with what? There is a specific kind of dietary fat call the triglyceride. As its name implies, it has a structural motif in which something is repeated three times. That something is a chain of carbons and hydrogens, hanging off in triplicate from a head made of glycerol, as the figure shows. Those three carbon-hydrogen chains, or fatty acids, are the “tri” in a triglyceride. Chains like this can be many carbons long.
Double X Extra: We call a fatty acid a fatty acid because it’s got a carboxylic acid attached to a fatty tail. A triglyceride consists of three of these fatty acids attached to a molecule called glycerol. Our dietary fat primarily consists of these triglycerides.
Triglycerides come in several forms. You may recall that carbon can form several different kinds of bonds, including single bonds, as with hydrogen, and double bonds, as with itself. A chain of carbon and hydrogens can have every single available carbon bond taken by a hydrogen in single covalent bond. This scenario of hydrogen saturation yields a saturated fat. The fat is saturated to its fullest with every covalent bond taken by hydrogens single bonded to the carbons.
Saturated fats have predictable characteristics. They lie flat easily and stick to each other, meaning that at room temperature, they form a dense solid. You will realize this if you find a little bit of fat on you to pinch. Does it feel pretty solid? That’s because animal fat is saturated fat. The fat on a steak is also solid at room temperature, and in fact, it takes a pretty high heat to loosen it up enough to become liquid. Animals are not the only organisms that produce saturated fat–avocados and coconuts also are known for their saturated fat content.
The top graphic above depicts a triglyceride with the glycerol, acid, and three hydrocarbon tails. The tails of this saturated fat, with every possible hydrogen space occupied, lie comparatively flat on one another, and this kind of fat is solid at room temperature. The fat on the bottom, however, is unsaturated, with bends or kinks wherever two carbons have double bonded, booting a couple of hydrogens and making this fat unsaturated, or lacking some hydrogens. Because of the space between the bumps, this fat is probably not solid at room temperature, but liquid.
You can probably now guess what an unsaturated fat is–one that has one or more hydrogens missing. Instead of single bonding with hydrogens at every available space, two or more carbons in an unsaturated fat chain will form a double bond with carbon, leaving no space for a hydrogen. Because some carbons in the chain share two pairs of electrons, they physically draw closer to one another than they do in a single bond. This tighter bonding result in a “kink” in the fatty acid chain.
In a fat with these kinks, the three fatty acids don’t lie as densely packed with each other as they do in a saturated fat. The kinks leave spaces between them. Thus, unsaturated fats are less dense than saturated fats and often will be liquid at room temperature. A good example of a liquid unsaturated fat at room temperature is canola oil.
A few decades ago, food scientists discovered that unsaturated fats could be resaturated or hydrogenated to behave more like saturated fats and have a longer shelf life. The process of hydrogenation–adding in hydrogens–yields trans fat. This kind of processed fat is now frowned upon and is being removed from many foods because of its associations with adverse health effects. If you check a food label and it lists among the ingredients “partially hydrogenated” oils, that can mean that the food contains trans fat.
Double X Extra: A triglyceride can have up to three different fatty acids attached to it. Canola oil, for example, consists primarily of oleic acid, linoleic acid, and linolenic acid, all of which are unsaturated fatty acids with 18 carbons in their chains.
Why do we take in fat anyway? Fat is a necessary nutrient for everything from our nervous systems to our circulatory health. It also, under appropriate conditions, is an excellent way to store up densely packaged energy for the times when stores are running low. We really can’t live very well without it.
Phospholipids: An Abundant Fat
You may have heard that oil and water don’t mix, and indeed, it is something you can observe for yourself. Drop a pat of butter–pure saturated fat–into a bowl of water and watch it just sit there. Even if you try mixing it with a spoon, it will just sit there. Now, drop a spoon of salt into the water and stir it a bit. The salt seems to vanish. You’ve just illustrated the difference between a water-fearing (hydrophobic) and a water-loving (hydrophilic) substance.
Generally speaking, compounds that have an unequal sharing of electrons (like ions or anything with a covalent bond between oxygen and hydrogen or nitrogen and hydrogen) will be hydrophilic. The reason is that a charge or an unequal electron sharing gives the molecule polarity that allows it to interact with water through hydrogen bonds. A fat, however, consists largely of hydrogen and carbon in those long chains. Carbon and hydrogen have roughly equivalent electronegativities, and their electron-sharing relationship is relatively nonpolar. Fat, lacking in polarity, doesn’t interact with water. As the butter demonstrated, it just sits there.
There is one exception to that little maxim about fat and water, and that exception is the phospholipid. This lipid has a special structure that makes it just right for the job it does: forming the membranes of cells. A phospholipid consists of a polar phosphate head–P and O don’t share equally–and a couple of nonpolar hydrocarbon tails, as the figure shows. If you look at the figure, you’ll see that one of the two tails has a little kick in it, thanks to a double bond between the two carbons there.
Phospholipids form a double layer and are the major structural components of cell membranes. Their bend, or kick, in one of the hydrocarbon tails helps ensure fluidity of the cell membrane. The molecules are bipolar, with hydrophilic heads for interacting with the internal and external watery environments of the cell and hydrophobic tails that help cell membranes behave as general security guards.
The kick and the bipolar (hydrophobic and hydrophilic) nature of the phospholipid make it the perfect molecule for building a cell membrane. A cell needs a watery outside to survive. It also needs a watery inside to survive. Thus, it must face the inside and outside worlds with something that interacts well with water. But it also must protect itself against unwanted intruders, providing a barrier that keeps unwanted things out and keeps necessary molecules in.
Phospholipids achieve it all. They assemble into a double layer around a cell but orient to allow interaction with the watery external and internal environments. On the layer facing the inside of the cell, the phospholipids orient their polar, hydrophilic heads to the watery inner environment and their tails away from it. On the layer to the outside of the cell, they do the same.
As the figure shows, the result is a double layer of phospholipids with each layer facing a polar, hydrophilic head to the watery environments. The tails of each layer face one another. They form a hydrophobic, fatty moat around a cell that serves as a general gatekeeper, much in the way that your skin does for you. Charged particles cannot simply slip across this fatty moat because they can’t interact with it. And to keep the fat fluid, one tail of each phospholipid has that little kick, giving the cell membrane a fluid, liquidy flow and keeping it from being solid and unforgiving at temperatures in which cells thrive.
Steroids: Here to Pump You Up?
Our final molecule in the lipid fatty trifecta is cholesterol. As you may have heard, there are a few different kinds of cholesterol, some of which we consider to be “good” and some of which is “bad.” The good cholesterol, high-density lipoprotein, or HDL, in part helps us out because it removes the bad cholesterol, low-density lipoprotein or LDL, from our blood. The presence of LDL is associated with inflammation of the lining of the blood vessels, which can lead to a variety of health problems.
But cholesterol has some other reasons for existing. One of its roles is in the maintenance of cell membrane fluidity. Cholesterol is inserted throughout the lipid bilayer and serves as a block to the fatty tails that might otherwise stick together and become a bit too solid.
Cholesterol’s other starring role as a lipid is as the starting molecule for a class of hormones we called steroids or steroid hormones. With a few snips here and additions there, cholesterol can be changed into the steroid hormones progesterone, testosterone, or estrogen. These molecules look quite similar, but they play very different roles in organisms. Testosterone, for example, generally masculinizes vertebrates (animals with backbones), while progesterone and estrogen play a role in regulating the ovulatory cycle.
Double X Extra: A hormone is a blood-borne signaling molecule. It can be lipid based, like testosterone, or short protein, like insulin.
As you progress through learning biology, one thing will become more and more clear: Most cells function primarily as protein factories. It may surprise you to learn that proteins, which we often talk about in terms of food intake, are the fundamental molecule of many of life’s processes. Enzymes, for example, form a single broad category of proteins, but there are millions of them, each one governing a small step in the molecular pathways that are required for living.
Levels of Structure
Amino acids are the building blocks of proteins. A few amino acids strung together is called a peptide, while many many peptides linked together form a polypeptide. When many amino acids strung together interact with each other to form a properly folded molecule, we call that molecule a protein.
For a string of amino acids to ultimately fold up into an active protein, they must first be assembled in the correct order. The code for their assembly lies in the DNA, but once that code has been read and the amino acid chain built, we call that simple, unfolded chain the primary structure of the protein.
This chain can consist of hundreds of amino acids that interact all along the sequence. Some amino acids are hydrophobic and some are hydrophilic. In this context, like interacts best with like, so the hydrophobic amino acids will interact with one another, and the hydrophilic amino acids will interact together. As these contacts occur along the string of molecules, different conformations will arise in different parts of the chain. We call these different conformations along the amino acid chain the protein’s secondary structure.
Once those interactions have occurred, the protein can fold into its final, or tertiary structure and be ready to serve as an active participant in cellular processes. To achieve the tertiary structure, the amino acid chain’s secondary interactions must usually be ongoing, and the pH, temperature, and salt balance must be just right to facilitate the folding. This tertiary folding takes place through interactions of the secondary structures along the different parts of the amino acid chain.
The final product is a properly folded protein. If we could see it with the naked eye, it might look a lot like a wadded up string of pearls, but that “wadded up” look is misleading. Protein folding is a carefully regulated process that is determined at its core by the amino acids in the chain: their hydrophobicity and hydrophilicity and how they interact together.
In many instances, however, a complete protein consists of more than one amino acid chain, and the complete protein has two or more interacting strings of amino acids. A good example is hemoglobin in red blood cells. Its job is to grab oxygen and deliver it to the body’s tissues. A complete hemoglobin protein consists of four separate amino acid chains all properly folded into their tertiary structures and interacting as a single unit. In cases like this involving two or more interacting amino acid chains, we say that the final protein has a quaternary structure. Some proteins can consist of as many as a dozen interacting chains, behaving as a single protein unit.
A Plethora of Purposes
What does a protein do? Let us count the ways. Really, that’s almost impossible because proteins do just about everything. Some of them tag things. Some of them destroy things. Some of them protect. Some mark cells as “self.” Some serve as structural materials, while others are highways or motors. They aid in communication, they operate as signaling molecules, they transfer molecules and cut them up, they interact with each other in complex, interrelated pathways to build things up and break things down. They regulate genes and package DNA, and they regulate and package each other.
As described above, proteins are the final folded arrangement of a string of amino acids. One way we obtain these building blocks for the millions of proteins our bodies make is through our diet. You may hear about foods that are high in protein or people eating high-protein diets to build muscle. When we take in those proteins, we can break them apart and use the amino acids that make them up to build proteins of our own.
How does a cell know which proteins to make? It has a code for building them, one that is especially guarded in a cellular vault in our cells called the nucleus. This code is deoxyribonucleic acid, or DNA. The cell makes a copy of this code and send it out to specialized structures that read it and build proteins based on what they read. As with any code, a typo–a mutation–can result in a message that doesn’t make as much sense. When the code gets changed, sometimes, the protein that the cell builds using that code will be changed, too.
Biohazard!The names associated with nucleic acids can be confusing because they all start with nucle-. It may seem obvious or easy now, but a brain freeze on a test could mix you up. You need to fix in your mind that the shorter term (10 letters, four syllables), nucleotide, refers to the smaller molecule, the three-part building block. The longer term (12 characters, including the space, and five syllables), nucleic acid, which is inherent in the names DNA and RNA, designates the big, long molecule.
DNA vs. RNA: A Matter of Structure
DNA and its nucleic acid cousin, ribonucleic acid, or RNA, are both made of the same kinds of building blocks. These building blocks are called nucleotides. Each nucleotide consists of three parts: a sugar (ribose for RNA and deoxyribose for DNA), a phosphate, and a nitrogenous base. In DNA, every nucleotide has identical sugars and phosphates, and in RNA, the sugar and phosphate are also the same for every nucleotide.
So what’s different? The nitrogenous bases. DNA has a set of four to use as its coding alphabet. These are the purines, adenine and guanine, and the pyrimidines, thymine and cytosine. The nucleotides are abbreviated by their initial letters as A, G, T, and C. From variations in the arrangement and number of these four molecules, all of the diversity of life arises. Just four different types of the nucleotide building blocks, and we have you, bacteria, wombats, and blue whales.
RNA is also basic at its core, consisting of only four different nucleotides. In fact, it uses three of the same nitrogenous bases as DNA–A, G, and C–but it substitutes a base called uracil (U) where DNA uses thymine. Uracil is a pyrimidine.
DNA vs. RNA: Function Wars
An interesting thing about the nitrogenous bases of the nucleotides is that they pair with each other, using hydrogen bonds, in a predictable way. An adenine will almost always bond with a thymine in DNA or a uracil in RNA, and cytosine and guanine will almost always bond with each other. This pairing capacity allows the cell to use a sequence of DNA and build either a new DNA sequence, using the old one as a template, or build an RNA sequence to make a copy of the DNA.
These two different uses of A-T/U and C-G base pairing serve two different purposes. DNA is copied into DNA usually when a cell is preparing to divide and needs two complete sets of DNA for the new cells. DNA is copied into RNA when the cell needs to send the code out of the vault so proteins can be built. The DNA stays safely where it belongs.
RNA is really a nucleic acid jack-of-all-trades. It not only serves as the copy of the DNA but also is the main component of the two types of cellular workers that read that copy and build proteins from it. At one point in this process, the three types of RNA come together in protein assembly to make sure the job is done right.
I finished assembling the requested cheddar cheese and cracker sandwiches and made sure to follow the precise directions for filling the sippy cups: half apple juice, half water, one ice cube, and a slice of lemon (don’t ask, my kids are high maintenance). Saturday afternoon was upon us and it was clear that we all needed a little downtime. So I set the girls up for a picnic on the family room floor, engaged Netflix, and laid out their snack. After a few minutes of getting comfy, calmness decided to pay us a visit. This was my carpe diem moment.
The perennial mint plant, known in my family as “El Jardin de Mojito.”
The weather could not have been more pleasant, and with the girls under the dear care of my best pal Pingu, I stepped out, barefooted, onto the deck. The sun caressed my cheeks. The wind whispered into my ear. The garden’s cologne was a reminder of my desire. Summer was seducing me and I did not could not resist.
I scanned the world before me, seamlessly moving my gaze from tree to tree, bush to bush, bird to bird, letting each thought morph into the next. I noticed the fluffy marshmallow clouds floating overhead and the sounds of a lawn mower humming in the distance. Then, at eleven o’clock, I caught a glimpse of the mint garden. The free flowing thoughts came to a screeching halt and my mind could focus on one thing and one thing only: Mojitos.
Belonging to the Lamiaceae family along with other aromatic herbs such as basil, oregano, and sage, mint has a tendency to spread rapidly and without care for the plants around it. But for us, this wasn’t an issue. Despite the vast culinary applications for this bountiful botanical, it is the quintessential ingredient for our favorite summer beverage, and so we’ve aligned ourselves with “the more the merrier” philosophy. After all, Greek mythology has dubbed mint as the “herb of hospitality” and what says “welcome to mi casa” more than the delicate sweetness of a cold mojito?
I didn’t bother to grab the scissors and made sure I followed the most direct route toward the mint patch. As I went to grab a large stalk, I noticed a little critter hanging out on one of the leaves. I lessened my grasp and began to examine the mint garden a bit more closely. It appeared to be a micro-ecosystem, bustling with tiny life forms.
Not wanting to miss a photographic opportunity, I ran back in, peeked in at the girls to make sure they were still there, and grabbed my camera (the good one). The snails were everywhere! My first reaction was “you best not be messing with the mojito garden!” But, upon closer inspection, these slow-moving, shelled cylinders of slime might be something more interesting, at least from a biological perspective.
Birds eye view of the European Amber Land Snail.
I knew that snails were mollusks, similar to clams and oysters, and that they could be further classified as gastropods, or “stomach foot” (to us, it looks like they are crawling on their bellies). But, I was having a hard time identifying the species to which these snails belonged, and that was probably because I was limiting my search to native species in NY State.
Frustrated, I turned to Ken Hotopp, conservation biologist and director of the environmental consulting company, Appalachian Conservation Biology. Ken informed me that these snails were amber land snails of the Succinea putris variety, which are native to eastern European countries and Great Britain, and further classified them as an invasive species.
Fred and Ethel, roaming the mint garden. Take a look at the “belly foot.”
When a species is classified as “invasive,” it typically means that they have high reproductive rates, can easily spread, and can quickly adapt to their new environment (a phenomenon called phenotypic plasticity). If these criteria are met, the invasive species can outcompete many of the indigenous species for resources and cause issues for the native habitat.
These snails probably made their way to the new world by hitching a ride on humans and despite the negative connotation associated with being an “invasive species,” it really isn’t their fault. They are just doing what they are biologically programmed to do: survive and pass on their gene pool to the next generation.
Regardless of origin, these snails looked beautiful to me. I love spiraling pattern at the rear of their calcium carbonate shells, and the way their tentacles, with eyes at the tip, scan their environment. It is really cool to watch the rhythmic motions of the foot, which can probably be plotted as a sine wave function in super slow motion.
Close up! Notice the patterns on the calcium carbonate shell, and the black eyes at the tip of the tentacles.
Realizing that time was of the essence (Pingu is effective for only so long), I zoomed out and started looking around for the best leaves to pluck. I said hello to the grasshopper that was probably banking on its green camouflage to keep it safe from predators, and took at look at the brilliant yellow flowers living atop the mint garden canopy. With the prize in hand, I ran into the kitchen, grabbed the simple syrup from the fridge (we always have some on hand), and began to make my mojito.
Within a few minutes, the finished product was in hand. But, alas, it would have to wait for I was being beckoned by the girls with the golden locks. I suppose one more episode of Pingu wouldn’t hurt.
Over the last few months, the concept of birth control has been under great scrutiny in the American eye. Many politicians have been discussing it’s “moral” implications, and whether institutions or organizations should have the right to deny insurance coverage for hormonal contraception if it does not fall within the confines of their belief systems. And while American women have narrowly escaped legislation that would impede their reproductive health and freedom, politicians, mostly men, feel it necessary to make misinformed or even completely false statements about birth control.
For some strange reason, there is this erroneous idea that birth control is not a matter of health, but rather a means by which a woman can engage in careless and frequent sexual activity, with a man, and without the consequences of pregnancy. It’s clear that the picture these politicians are trying to paint is that of debauchery and immorality, which, of course, is a departure from the puritanical integrity they embody. But, rather than focus on this utter nonsense, I would prefer to highlight the significant impact birth control will have on the future of our civilization and our planet.
The human population has grown steadily since the beginning of our species. However, the rate of growth began to skyrocket after the industrial revolution, and our population has actually doubled over the last 50 years, reaching 7 the billion mark in March of this year. This is an astounding statistic since it took until 1804 – around 50,000 years – to reach our first billion.
World Population: 1800 – 2100 (Wikimedia Commons)
What makes these numbers really scary is the concept of carrying capacity, which is an ecological term used to describe the maximum number of individual members of a species that a certain habitat can support. In this case, the species is human and that certain habitat is planet earth.
Here’s the thing: the availability of our resources will not match the rate of population growth. Given our current technologies, there is only so much food we can grow, only so much water we can drink, only so much space we can inhabit, only so much waste we can safely rid, only so much energy we can harness. There will be a point that the human population will hit its carrying capacity on earth, and when it does, the chances of widespread famine will be great, and the delineation between the developing world and the developed world will be no longer.
Given this very serious issue, Britain’s Royal Society has recently convened to discuss the future of the human population and on April 26th, 2012, and published their findings in the People and the Planet Report [PDF]. For me, key findingnumber three struck a cord:
Reproductive health and voluntary family planning programmes urgently require political leadership and financial commitment, both nationally and internationally. This is needed to continue the downward trajectory of fertility rates, especially in countries where the unmet need for contraception is high. (emphasis theirs)
Political leadership and financial commitment – Did you see that, American politicians?? For those of you who are unnecessarily waging war on women’s reproductive rights, its time to get your giant heads out of your collective asses and realize the implications of legislation that would go against ensuring both the continued success of our species and the health of our planet. It is time to stop spending money on these regressive and oppressive campaigns guised under the false pretense of “religious freedom” and start making a financial commitment to the women (and by association, men) who live in our nation.
To drive this point even further, here is another excerpt from the People and the Planet Report (my favorite bit, found in Box 2.5 on page 33):
Women bear the main physical burden of reproduction: pregnancy, breastfeeding and childcare. They also bear the main responsibility for contraception as most methods are designed for their use. Men, it may be argued, reap the benefits of children without incurring an equal share of the cost. It follows that women may be more favourable to the idea of small families and family planning than their partners but unable to express their inclinations in male-dominated systems. Such views received international endorsement in the Program of Action resulting from the UN conference on population in 1994. Paragraph 4.1 states that “improving the status of women is essential for the long-term success of population programs”.
We currently live in a nation where 99% of women who are of reproductive age have used some form of birth control at least once. And when it comes to hormonal contraception, over 80% of sexually active women aged 15-44 have relied on “the pill” as a means to prevent unwanted pregnancies. This has contributed to an average of two births per American woman, which is considered to be the replacement rate for a population. Compare this number to countries where birth control and reproductive education is scarce – countries like Niger (7.52 births per woman) or Afghanistan (5.64 births per woman) – and one can see the impact of family planning through contraception. Furthermore, it has been well documented that women in developed worlds who are provided with the means to control their fertility are more empowered and their families are healthier.
While our situation in the US is significantly better compared to underdeveloped nations where rape and the cultural devaluing of women is commonplace, we still have a responsibility to uphold – a responsibility that would undoubtedly increase the quality of life for women (and men), as well as contribute to the overall health of the human population. Why would we want to go backwards and remove the ability of a woman to decide when, if ever, she would like to reproduce?
Having access to birth control empowers women and allows them to make greater contributions to society. And because contraception is primarily the responsibility of a woman, our society needs to ensure that birth control, reproductive education, and family planning resources are readily available to EVERYONE.
The United Nations predicts that the ten-billionth person will be born around 2050. Will we continue to fight this ridiculous fight against women’s rights or will we redirect our collective energy to developing technologies that will help our species and planet better cope with the increasing demands associated with a steadily rising population? Let’s stop allowing stupidity to prevail and let’s start doing the right thing: making sure that birth control is readily available to any woman who wishes to use it. Because, now more than ever, it is clear that birth control will save the world.
Note: In my readings for this article, I came across a wonderful resource for anyone interested in learning more about human fertility and population growth. Through the wonders of the internet, Academic Earth is offering a free (!) online course called Global Population Growth, given by Yale University professor Robert Wyman.
These views are the opinion of the author and do not necessarily either reflect or disagree with those of the DXS editorial team.
Blueberries in the Northwestern semisphere are the fruit of several shrubs in the genus Vaccinium L. They grow in all provinces in Canada and all but two of the United States (Nebraska and North Dakota). In the Northwestern semisphere, one can find 43 species of blueberries, depending on the region. Blueberries are found and produced in all hemispheres of the world. However, the species can vary by region.
Kingdom: Plantae (Plants)
Subkingdom: Tracheobionta (Vascular plants)
Subdivision: Spermatophyta (Seed plants)
Division: Magnoliophyta (Flowering plants)
Class: Magnoliopsida (Dictyledons)
There are 43 species and 46 accepted taxa overall. Some of the species include fruits we do not necessarily recognize as blueberry, including farkleberry, bilberry, ohelo, cranberry, huckleberry, whortleberry, deer berry, and lingonberry. (Source)
Blueberries are a very popular fruit in the U.S., and is consumed in fresh, frozen, and canned forms. While blueberries are a great fruit to eat to meet your suggested fruit intake, it also is one of the foods that are purported to have properties that it just does not have. This undeserved reputation results from the high levels of anti-oxidants, leading those predisposed to looking for “super foods” to classify blueberries into the anti-oxidant super food category. While eating more healthy foods is always a good idea, no food has curative effects all on its own.
Other aspects of blueberry nutrition includes it as a source of sugar. One cup (148 g) of blueberries contains about 15 g of sugar and 4 g of fiber, a single gram of protein, and half a gram of fat. If you are counting carbs, this cup has 21 g of them. That one cup of blueberries averages about 85 calories, which is approximately the same as a medium apple or orange. While almost all the vitamins and minerals nutrition gurus like to report on are present to some amount, for the 2000-calorie diet, that one cup of blueberries will provide the recommended daily value of 24% of Vitamin C, 36% of Vitamin K, and 25% of manganese. The remaining values range from 0-4%. (Values obtained from Nutrition.com and verified through multiple sources.)
The Wikipedia entry is quite good and well researched (as of August 18, 2012).
The photo above shows all of the life stages of a blueberry. Berries go from the little red nub at the end of the branch to round and juicy blueberries through fertilization of the ovary, which swells rapidly for about a month, then its growth ceases. The green berry develops with no change in size. The chemicals responsible for the blue color, anthocyanins, begin to turn the berry from green to blue as it develops over about 6 days. The volume of the berry increases during the change in color phase.
Will blueberries turn you blue? In short, no. You can achieve blue skin through the ill-advised practice of drinking silver or you can achieve orangish-yellow skin by eating a large number of carrots. This is because the chemicals causing the skin color are fat soluble and are present in a large quantity in the fat just under the skin, giving the skin those colors. Anthocyanin, the primary chemical causing the blue color in blueberries, is not fat soluble and will not reside in the fat under your skin.
Anthocyanins is a class of over 30 compounds. The chemical structure is generally as shown below. They are polyphenolic, which indicates the 3 ring structures. The “R” indicates different functional groups that change depending on which anthocyanin the structure represents.
Interestingly, anthocyanins are also pH indicators because their color ranges from yellow to red to blue depending on the local pH. The blue color indicates a neutral pH. The wikipedia page on anthocyanins is also informative (as of August 18, 2012).
1/2 – 1 pint blueberries, fresh or frozen (defrosted)
Food coloring, optional
2 cups all-purpose flour
1/4 tsp. salt
1 Tbsp. baking powder
Your favorite mini-treat (Hershey’s Kisses, Hugs, Reese’s Mini Cups, strawberry jam, etc.)
Preheat the oven to 350º. In a large bowl, cream the butter and sugar. You can use a wooden spoon, a potato masher or handheld electric mixer. Mix in the eggs, one at a time, and add the milk.
Rinse the strawberries and cut off the green stem. Mash the berries with a potato masher or puree in a blender. Then stir the berries into the butter and milk mixture. TIP: For muffins with a more blue color, add a few drops of blue food coloring.
In a separate bowl, sift the flour, salt and baking powder. Stir well. Add the flour mixture to the berry mixture. Use a wooden spoon to stir until all the white disappears.
Line the muffin tin with paper liners. Drop the batter from a tablespoon to fill the cups halfway.
Add a surprise: an unwrapped mini treat or 1/2 teaspoon of jam. Then spoon more batter to fill almost to the top.
Bake until the muffins begin to brown and a toothpick inserted near the center (but not in the mini-treat) comes out clean, about 20-25 minutes.
Remove the muffins from the tin and cool.
Or perhaps you are in less of a cooking scientist mood and more in a home lab mood. Try this at-home lab with blueberries about dyes. Adapted from the Journal of Chemical Education.
Items You Need
4 microwavable/stove top staff glasses, pots, or containers at least 1/2 cup in volume
tablespoons or 1/4 cup measuring cup
alum (available in the grocery store spice aisle)
cream of tartar (available in the grocery store spice aisle)
hot pads and tongs
at least four small (1-2 in.) squares of white cotton cloth
yellow onion skins
notebook for experimental observations
In each step, you will want to record your observations, paying special attention to colors.
Pour 4 tablespoons (1/4 cup) into container 1. Add a pea-sized scoop of alum and about half that amount of cream of tartar and stir. Bring the solution to a boil on the stove top or by microwaving for about 60 seconds. (Your microwave may vary.) Add two small squares of white cotton cloth and boil for two minutes. Set the container aside. The squares will be used in steps 4 and 6.
Tear the outer, papery skin from a yellow onion into pieces no more than 1 inch square. Place enough pieces in a second container to cover its bottom with 2 or 3 layers of onion skin. Add about 4 tablespoons of water to the container. Bring the solution to a boil on the stove top, continuing to boil for 5 minutes.
Wet a new square of cloth with water. Place it in container 2 so it is completely submerged and boil for 1 minute. Using tongs, remove the cloth and rinse it with water. Place the cloth square in the appropriate area on a labeled paper towel.
Use tongs to remove one of the cloth squares from beaker 1. Repeat step 3 using this square. Compare to the dyed cloth square from step 3.
Pour 4 tablespoons of water in a third container. Add 4-5 blueberries to the container and mash them with a spoon. Bring the solution to a boil on the stove, and continue to boil for 5 minutes.
Repeat steps 3 and 4 substituting the blueberry mixture in container 3 for the onion skin mixture in container 2.
Mix a small scoop of baking soda with a tsp of water in a clean container. With a dropper, place 1-2 drops of the baking soda solution in one corner of each cloth square. What happens? Rinse the dropper thoroughly, then place 1-2 drops of vinegar on the opposite corner of each square. What happens? Rinse the fabric squares under cool running water. Is there a change? Allow the squares to dry overnight. Is there any change of the cloth dries?
Optional: Try variations in the procedure such as changing the amount of dye source, the length of time the cloth spends in the dye solution, and the temperature of the dye solution.
Questions to consider
The solution in step 1 is called a mordant. Based on your observations, what is the purpose of a mordant?
Is the dye produced by blueberries really blue? Why might some people not want to wear clothes dyed with blueberries?
All in all, enjoy your blueberries. As a shrub, it is quite pretty. As a fruit, it is quite yummy. And as the tool in an experiment, it is quite fun.
These views are the opinion of the author and do not necessarily reflect or disagree with those of the DXS editorial team.