Biology A2 (F215) Control, Genomes and Environment

A2 Biology OCR F215

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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

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Polypeptides coded for...

  • 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

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The code

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
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The first stage of protein synthesis 

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