Biology A2 (F215) Control, Genomes and Environment

• 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

• Structural- collagen, keratin
• Haemoglobin
• immunoglobulin (antibodies)
• cell surface receptors
• muscle cells
• tubulin in the cytoskeleton
• channel proteins
• electron carriers
• enzymes

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