Lecture nov 6 Bact. Translation, Intitiation Flashcards
3 steps of translation?
initiation, elongation, termination
How much is the complete bacterial ribosome?
70S
Purpose of large subunit?
Catalyzes reaction of peptide bond forming
Small subunit purpose
Holds mRNA and binds it, finds start codon
How many sedimentation units is a complete bacteria?
70S (50S+30S)
What is Sedimentation rate? What units is it in?
Sedimentation rate: a measure of how fast a particle of a given mass, size and shape settles when subjected to a centrifugal force.
Svedberg unit (1S = 10^-13 seconds)
What generally happens at initiation stage?
The ribosome forms on the mRNA
1. the small subunit binds to the mRNA. (start codon is in P site)
2. initiator tRNA binds to the Psite
3. Complete ribosome unit: Large subunit comes in and sticks on to small unit to
General idea of initiation stage?
Ribosome unit forms on the mRNA
What is the initiator tRNA?
fMet-tRNA^ini
Has a methioine with a formaldehyde group.
What are the long steps of initiation, before the 70S subunit joins, bacterial?
Set up for small ribosome binding to mRNA
1. IF2GTP and IF3 enter small ribosome
2. IF1 joins
Binding to mRNA
3. mRNA and tRNA initiator bind to the small ribosome (VERY unstable)
4. mRNA unfolds
5. Structure LOCKS: initiator tRNA binds to start codon NOW stable
What happens after the 70S subunit joins the 30S subunit
- 70Sbinds to 30S
- IF2-GTP breaks down into GDP+Pi
- Causes all units inside small ribosome subunit to move to big subunit
- IF1 and IF3 leave
- Pi and IF2 leave
What is the conformational change?
When all the units in the 30S subunit move to the 50S subunit
What ends off in the ribosome subunit at the end?
Just the tRNA and the mRNA.
(IF2 and Pi leave last).
During initiation, when is the complex very unstable?
When the tRNA and mRNA first enter the 30 S subunit
What is the end product of the initiation step?
Ribosome is complete
What happens at elongation stage?
What happens at termination stage?
What is an initiator tRNA?
A tRNA holding a methionine. First tRNA to enter subunit
What are the 3 different sites on ribosomes and what are they used for?
A, P and E site
for tRNAs, mRNAs and other proteins to bind to.
Which site does the catalytic activity happen?
P site. Makes peptide bonds with other amino acids
What is the E site for?
2 major functions of ribosome?
- Small subunit aligns two tRNAs via codon-anticodon recognition
- Large subunit catalyzes peptide bond formation
What are release factors?
Proteins that help stop translation
