Genetic Control of Protein Structure

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  • Genetic Control of Protein Structure
    • Mutations
      • transition; base change
      • transversion; swap base with opposite one
      • Missense mutation; change from one amino acid to another
      • Nonsense; change from one amino acid to a stop codon
      • Neutral; change from one amino acid to another similar one
      • Silent; change in codon so that the same amino acid is specified
      • Frameshift; addition or deletion of one or a few base pairs leads to a change in reading frame
    • Spontaneous mutation
      • Due to wobble base pairing e.g guanine can wobble base pair with thymine during replication producing one wild type and one mutant
      • Due to looping out errors during DNA replication. Can lead to base insertion or base deletion.
      • Chemical changes; depurination - adenine or guanine is lost from the DNA backbone. If not repaired a random base is inserted
        • Deamination - cytosine is deaminated to uracil. If not repaired uracil pairs with adenine
      • Mutation rate of 1.1x10-8 per position per haploid genome
    • Induced Mutations
      • Ionising, xray  Have high energy which can break covalent bonds leading to point mutations
      • UV radiation; low energy causes pyrimidine dimers between and within stands. Leads  to DNA replication problems
      • Chemical
        • Base analogues e.g. 5-bromouracil normally pairs adenine but it can also pair guanine - transition mutation
        • Base modifiers alter the chemical structures of bases e.g. alkylating agents like MMS, methylguanine pairs thymine
        • Addition/deletion mutation caused by an intercalating agent
    • Sickle cell anaemia
      • Recessive mutation in haemoglobin that affects its ability to bind to oxygen
        • At low oxygen the rbc loses concave shape and becomes sickle shaped
      • Missense mutation at residue 6 of Hb-A changing glutamate to valine. Replacing a charged residue with a neutral one. Change observed by electrophoresis
    • Evolution
      • Dominant traits are usually gain-of-function. Recessive traits are usually loss-of-function
      • Conserved motifs (sequences). E.g. SH2 in drosophila and humans. Structurally conserved protein domain within the Src oncoprotein
      • Proto-Oncogene tyrosine protein kinase is a non-receptor protein tyrosine kinase that is encoded by the Src gene.The sequence alignment of Src kinases from various phyla is similar
        • Molecular recycling; protein designs are duplicated, adapted and modified

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