mutations

• insertion= extra base inserted into strand. This shifts the reading frame (frameshift).
• Substitution (Point mutation): one base substituted for another.
• Deletion= one base is deleted from the strand, also a frameshift.
• Mutations in a protein usually only make a difference when they occur at the binding site causing it to change shape.
• Mutation= change in the sequence of bases on a DNA strand.
• Types of mutations:

  • substitution
  • insertion
  • deletion
• Effects of mutation:

  • silent
  • nonsense
  • missense
• Silent= no change to the amino acid coded for.
• Nonsense= codon transformed into a stop codon, results in a shortened protein.
• Missense= incorrect amino acid into primary structure
• Mutations can be conservative (not severe) or non-conservative (severe).
• Mutations can be both harmful and beneficial (e.g. variations like certain insects being more camouflaged).
• Operon= group of genes that are under the control of the same regulatory mechanism and are transcribed at the same time
• lac operon= group of three genes, lacZ, lacY and lacA, involved in the metabolism of lactose
• The binding of RNA polymerase still only results in a relatively slow rate of transcription that needs to be increased to produce the required quantity of enzymes to metabolise lactose efficiently. This is achieved by the binding of cAMP receptor protein.
• Protein kinases are enzymes that catalyse the addition of phosphate groups to protein. The addition of a phosphate group changes the tertiary structure and so the function of the protein. Protein kinases are often activated by cAMP.
• Homeobox= section of DNA 180 base pairs long coding for a part of the protein that is highly conserved in plants, animals and fungi. This part of the protein, a homeodomain, binds to DNA and switches other genes on or off. Therefore homeobox genes are regulatory genes.
• Hox genes are one group of homeobox genes that are only present in animals. They are responsible for the correct positioning of body parts.
• Post-translational control:

  • addition of non-protein groups (e.g. phosphates or lipids)
  • folding or shortening of proteins
  • modification by cAMP
  • modifying amino acids and the formation of bonds
• Translational control:

  • degradation of mRNA-the more resistant the molecule the longer it will last in the cytoplasm so a greater quantity of protein synthesised
  • binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins
  • activation of initiation factors which aid the binding of mRNA to ribosomes