Protein Synthesis

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  • 11: Protein Sythesis
    • Central dogma; amplification occurs at each stage. DNA(2 copies) - mRNA(10-15 copies) - Protein(>100)
    • Ribosome
      • Form nissl substance, form polyribosomes (many on one strand) so many can be made
      • Made of large and small subunit. Contains 3 binding sites (A,P,E). A = amino-acyl trna P = peptidyl trna E = exit
      • mrna spooling (movement) site is the smaller subunit
    • Antibiotics
      • Selectively inhibit protein synthesis. Side effects due to similarity of mitochondria land bacterial protein synthesis.
        • Actinomyoson D; binds to dna and blocks the movement of rna polymerase (transcription blocker)
        • Cycloheximide; blocks the translocation reaction on ribosomes (translational blocker)
    • Translation cycle
      • Amino acyl trna binds to A site. Amino acyl trna occupies p site and cause a conformationchange. Large subunit transclocates leaving two trnas in hybrid states. Small subunit translocates 3 nucleotides. Spent mrna ejected. Leaves a full empty A site
      • Elongation factors
        • correct base pairing of trna and mrna promotes EF-TU gtpase activity. GDP bound to EF-tu dissociates from complex. Cause amino acyl trna to be captured. Incorrect base pairing gives not gtpase activity (error check)
        • EF-G in gtp bond binds to A site once large subunit has translocated. Promote movement of trna into hybrid state (A/P P/E). Gtp hydrolysis of EFG changes shape of ribosome and cause moment of trnas intro p and e site when small unit translocates
    • Initiation
      • Translation starts at Met (aug). Carries methionine (f-met bacteria)
      • Initiator trna loaded onto small ribosome unit at p site with initiation factor EiF-2 (eucaryote initiation factor). Starts to move along strand to find first aug. Once found ELF dissociates. Large subunit then comes and binds. Initiation rna still bound at p site. Amino acyl trna enters site A
    • Termination
      • Stop codons not recognised by trna. Release factors bind to a site, Peptidyl transferase catalyses transfer of water to c terminus. This dissociates peptide from ribosomes. Release factors in p promotes ribosome disassembly


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