Zoology101: Animal Biology Last Lecture Outline Lecture 12 1. Transcription2. Eukaryotic Initiation 3. TranslationCurrent Lecture 1. Translation continued• initiation• elongation• termination2. Posttransational localization and Cotransational localization3. Mutations • Point mutations 4. Protein folding and Protein destruction in a cellTranslation continued • Ribosomal subunits will joing for translation• Initiation◦ mRNA binds to small subunit, 5 prime cap helps with postioning◦ anticodon of initiator tRNA (tRNA met) binds to start codon◦ Large subunit binds • Elongation◦ polypeptide gets longer◦ anticodon of next charged tRNA binds to codon on A site (Codon recognition)◦ tRNA-met bond broken, met forms peptide bond with next amino acid (peptide bond formation)◦ translocation: ribosome moves down mRNA; A site is vacant ◦ uncharged tRNA in E site exits • Termination◦ stop codon enters A site ◦ release factor binds in A site◦ Complex falls apart Post-transational and Co-transational Localization• Post-transational: protein folds and goes to final destination • Co-transational: gets an ER signal peptide and sent to the ER while still being made◦ translation starts on the cystolic ribosome◦ signal recognition peptide binds to signal peptide and translation HALTS ◦ whole complex dragged to ER◦ Complex attaches to translocation complex and translation resumes◦ Protein imported into ER, signal peptide cleaved, Protein folds Mutations • Change in organisms DNA • How?◦ Mistakes happen during DNA replication◦ Damage after DNA replicaiton (thiamine dimer)• Point mutations◦ base substitutions◦ deletion/insertion◦ change amino acid • base substitution◦ replacement of one pair of nucleotides with another ◦ Silent: no change in amino acid sequence, consequences; not often◦ Missense: change amino acid sequence, consequences vary, sickle cell anemia ◦ Nonsense: insertion of a stop codon, consequence: shortened protein, ALWAYS BAD • Deletion/Insertion◦ addition or loss of nucleotide, resulting in a frame shift◦ frameshift mutation: new/wrong reading frame, everything off by one, wrong protein will be made◦ Frameshift causing nonsense: truncated protein, stop codon is added. Protein folding and Protein destruction in a cell • ubiquitin: protesome system, tag put on to be destroyed • ubiquitin protein ligase: attaches ubiquitin to doomed proteins • Proteosome: chops up ubiquitin
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