What is a gene?
- Length of DNA - a sequence of nucleotide bases - codes for polypeptides
- Human genome- 25000 genes
Genes are found...
- In the mitochondria (small number)
- Most are on the linear chromosomes in the nucleus
Each gene has a specific locus on the chromosome
A chromosome is a molecule of DNA and a gene is just part of the molecule
The DNA is associated with histone proteins
Polypeptides coded for...
- Structural- collagen, keratin
- immunoglobulin (antibodies)
- cell surface receptors
- muscle cells
- tubulin in the cytoskeleton
- channel proteins
- electron carriers
Because genes code for enzymes, they have an active role in every metabolic process
These are a sequence that provides the code for constructing a polypeptide chain.
The characteristics are...
- A triplet code- codes for an amino acid
- there are 4 bases so the number of sequences is 64
- Only 20 sequences are needed for protein synthesis
- It is a degenerate code
- all amino acids but Methionine have more than one code
- some codes signify STOP
- Codes are sometimes the same in different organisms but it is not necessarily true
The first stage of protein synthesis