Protein Synthesis
- Created by: Alice Fisher
- Created on: 11-05-15 12:19
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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)
- Selectively inhibit protein synthesis. Side effects due to similarity of mitochondria land bacterial protein synthesis.
- 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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