DB Lecture 27: Translation Mechanism II and Regulation Flashcards
What impact does dwell time have on incorporation of the “correct” amino acid in a growing peptide chain?
longer dwell times…
indicate correct complementarity of the anticodon and codon allows the GTP-bound eEF1A to hydrolyze GTP
What are the steps of elongation?
nest aa-tRNA is escorted to the A site of the ribosome by eEF1A (bound to GTP); hydrolysis of GTP to GDP by GAP on ribosome –> eEF1A leaves complex; peptidyl transferase reaction binds the Met from the Met-tRNA to the top of the new aa-tRNA; translocation hydrolizes GTP to shift ribosome so that the Met-tRNA (now cleaved of the Met) is in the E binding site, the new aat-RNA (now also bound to Met) is in the P binding site, and the A binding site is open for the next aa-tRNA
What regulates which aa-tRNA is used at the P site?
the codon-anticodon interaction between the sequence of the mRNA and the anticodon arm of the tRNA which allows for the correct timing for the hydrolysis reaction to proceed
What is required for incorporation of one amino acid in a growing polypeptide chain?
hydrolysis of four high-energy bonds (two in the aa-tRNA synthase reaction and two in the elongation reaction)
What are polysomes?
multiple ribosomes translating a single mRNA
What induces termination?
a ribosome arriving at a stop codon (this releases it from the mRNA)
Provide examples of common stress signals.
Ca2+ release from ER LPS heat shock TNF-alpha virus infection GF deprivation AA starvation heme deficiency
What is eIF2?
an initiation factor that is required to present initiator tRNA to the ribosomal P site
when phosphorylated it cannot switch from the inactive GDP-bound state to the active GTP-bound state
How do cells respond to stress signals?
activation of one of a number of protein kinase that phosphorylate eIF2 (initiation factor required to present initiator tRNA to the ribosomal P site)
What happens to cells in response to stress (rapamycin) or poor growth conditions?
mTOR is inactivated
4E-BP binds to the eIF4E
overall translation initiation is reduced
What happens to cells in the absence of stress (rapamycin) or in good growth conditions or in cancer cells?
mTOR phosphorylates 4E-BP
the eIF4 complex is released
overall translation initiation is increased
What is SUTR regulation?
regulatory proteins that bind to specific UTRs (can be hairpin loop structures formed by intramolecular base pairing) on the mRNA that interfere with scanning
What is RNAi?
a naturally occurring mechanism that cells use to down-regulate specific gene expression via inhibitor of small translation
What can RNAi be used for in research?
introduction of exogenous siRNA allows for “knock-down” of expression of a target gene
