Eukaryotic translation initiation factors and poly a

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Eukaryotic translation initiation factors and poly-A binding protein shape mRNA into a circle o Prepares for translation o Stabilizes mRNA RNA Splicing o Removes introns in 5’ to 3’ untranslated regions (UTRs) and all codons
o Joins exons to form a mature mRNA o Spliceosome 4 snRNPs snRNAs o Ribozymes o Introns are not “junk” DNA Alternative Splicing o Produces different mRNA molecules o Tailors primary transcript to produce more than one kind of protein o Introns may play a role Translation and Post-Translational Processing Transfer RNAs Mediate Translation tRNA o Contain modified bases o Carry particular amino acids Structural levels o Primary: nucleotide sequence o Secondary: Cloverleaf shape o Tertiary: Letter ‘L’ Structure o Anticodon: Nucleotides complementary to mRNA codon Found at one end of ‘L’ o Aminoacyl-tRNA synthetases Connect tRNA to amino acid Molecular translators Wobble o “promiscuous” base pairing between codons and anticodons Flexibility in 3’ nucleotide of codon and 5’ end of anticodon= wobble o Crick’s wobble rules 5’ end of anticodon – 3’ end of codon G------------------------------U or C C------------------------------G A------------------------------U U------------------------------A or G Ribosomes: Polypeptide Synthesis o Ensure accurate representation of genetic code o Structure Prokaryotes 30S subunit 50s subunit Eukaryotes 40S 60S
o Functional domains 30s: initial binding 50s: peptidyl transferase A site, P site, E site Translation Initiation: prokaryotic Ribosome binding site o Shine-Dalgarno box o AUG: fMet 16S rRNA and fMet tRNA bind 50S associates with 30S Initiation factors Ends with fMet tRNA in P site of completed ribosome Initiation: Eukaryotic Ribosome binding site o Methylated cap o AUG: Met Met tRNA binds 60S associates with 40S Initiation Factors Ends with Met tRNA in P site of completed ribosome Elongation Peptidyl transferase binds amino acid in P site to aa in A site Ribosome moves tRNA in P site moves to E site while tRNA in A site moves to P site, and new tRNA enters A site Polyribosome Termination Release factors recognize termination codons tRNA and mRNA separate from ribosome Ribosome dissociates into subunits
Posttranslational Processing Posttranslational modifications o Cleavage into polyprotein o Addition of chemical constituents Differences between prokaryotes and eukaryotes in gene expression Questions: During transcription, in which direction does the RNA polymerase read the DNA template strand?
During translation, in which direction does the ribosome read the mRNA strand?

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