Lecture nov 11 L. 10.3 Flashcards
What is left before we start elongation?
Ribosome subunits connected, with the initiator tRNA and the mRNA in P site
What are the steps for elongation?
- Substrate binding (EF-Tu-GTP putting aminoacyl-tRNA into A-site)
- Transpeptidation
- Translocation
What are the steps for elongation?
- EFTu ataches to a.a tRNA
- brings a.a tRNA to A-site
- If correct codon/anticodon pairing, releases a Pi and leaves aminoacyl tRNA there
What direction does protein sunthesize in?
N to C direction
What powers elongation?
GTP (*means what?)
What causes the EFTu to let go of the tRNA
Hydrolysis (GTP to GDP)
If the codon anticodon match is correct, the Small subunit will signal EFTu-GTP to become GDP and will cause it to let go and push away from the A site.
Leaving
What does the EF-Tu ribosome do?
Attaches to the Aminoacyl-tRNA and Drops off in the A site of the ribosome.
What happens if the EFTu puts the incorrect tRNA vs correct?
If its the incorrect match, hydrolysis will NOT occur so the EFTu will stay attached to the aa-tRNA and will leave with it
What does the EFTu do after it’s dropped off the tRNA?
Leaves
When is EFTu open vs. closed.
Closed= has a SMOOTH tRNA binding site, so can bind to tRNA (has GTP)
Open= has s ROUGH tRNA binding site, can NOT bind to tRNA (has GDP)
What happens to EFTu after dropping off tRNA?
gets rid of GDP and finds another GTP. So it can find another tRNA
What is transpeptidation?
Breaking bond to tRNA and making new bond to amino acid beside
(eventually makes a protein)
What occurs during translocation?
- the Ratchet motion, where the top half of the tRNA is moved by the 50S ribosome
- Power stroke, where EF-G-GTP (another elongation factor) moves rest of tRNA to new binding site
What occurs after the power stroke
the small subunit rotates back to its orginal position
When does termination occur?
When a stop codon enters A site
