BIOL-L211 Lecture 31 Outline of Last Lecture I. ArticleII. TranslationIII. Ribosome CompositionOutline of Current Lecture I. Recruiting Ribosome to mRNA transcriptII. Initiation of Prokaryotic TranslationIII. Initiation of Eukaryotic TranslationIV. Eukaryotic TranslationCurrent LectureTranslation II. Recruiting Ribosome to mRNA transcriptA. Prokaryotes1. Ribosomal Binding Site (RBS): consensus sequence 3-9 bp upstream of the start codon recognized & bound by ribosomes2. In prokaryotes, consensus is 5'-AGGAGG-3'B. Eukaryotes1. 5' cap responsible for recruitment of ribosome2. After recruitment, ribosome binds and scans to find the start codon3. Kozak Sequence: eukaryotic consensus sequence that increases the efficiency of translation (includes bases upstream and downstream of the start codon- includes AUG) C. Note that the start codon must always be placed in the P siteThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.E. Polysome: Translation efficiency can be increased with the binding of multiple ribosomes (polyribosomes); increases protein output from a given transcript1. Each ribosome can only produce one protein at a timeII. Initiation of Prokaryotic TranslationA. Initiator tRNA (prokaryotes): specialized with a methionine with a formyl group attached (fMet)1. Anticodon and start codon pair in P siteB. Initiation Factors (IF): proteins that facilitate translation initiation in prokaryotes1. IF1: Binds A site (prevents tRNA from entering A site)2. IF2: Binds IF1 and will (with GTP) help recruit initiator tRNA to bind to the small subunit (after IF3 is in place)3. IF3: Binds E site (prevents tRNA from entering E site)C. Initiator tRNA and mRNA recruited to small ribosomal subunit1. rRNA component of ribosome recognizes RBS and binds (base pairs)2. Start codon at P site3. Initiator tRNA comes to P site4. After mRNA and tRNA are recruited, large subunit comes5. IF1, IF2, and IF3 leaveIII. Initiation of Eukaryotic TranslationA. Eukaryotic Initiation Factors (eIF): proteins that facilitate translation initiation in eukaryotes1. eIF1, eIF1A, and eIF5: block A and E sites so that charged initiator tRNA can enter P sitea. Note: In eukaryotes, initiator tRNA has just an ordinary Met (no fMet)2. eIF4E: binds the 5' cap of mRNA, cooperates with other mRNA-associated initiation factors to interact with ribosome-associated initiation factors in the small subunitB. Initiator tRNA is aligned in P site1. Small ribosomal subunit and its eukaryotic initiation factors search mRNA 5' to 3' for start codon2. Once found, large subunit recruited3. eIFs leave E and A sites and translation beginsIV. Eukaryotic TranslationA. Circular Structure1. eIF4G: protein that interacts with the poly-A tail and poly-A binding proteins to make a ring structure of mRNA to facilitate translationa. Helps binding of eIF4Eb. Helps recruit large subunitc. Makes translation more efficientd. Limits degradation (eventually degrades
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