Biol 305- Mechanisms of Translation

get ready for proteins!

enzyme which charges tRNA’s:

aminoacyl tRNA synthetase

loop in tRNA responsible for interacting with the codon:

anticodon loop

loop in tRNA responsible for interacting with the amino acid:

acceptor loop

Wobble Theory:

The first two bases of a codon will exhibit strong Watson and Crick base pairing, but the third can have nontypical base pairing, allowing a single tRNA to recognize multiple codons

A site function:

accepts new charged tRNA’s

P site function:

new peptide bonds are created from new amino acid in A site and chain in P site with peptidyl transferase activity

E site function:

site of exit for an uncharged tRNA

puromycin resembles a tRNA but causes ________ when incorporated into the A site

premature termination

Steps to prokaryotic Initiation:

1. 30S complex forms (small subunit, mRNA, 1st tRNA)

2. IF2 is bound to GTP which recruits tRNA

3. IF1 and IF3 leave the complex to allow the large subunit to bind'

4. GTP is hydrolyzed to promote IF2 leaving and is a checkpoint for correct assembly

IF1 function in prokaryotic initiation:

promotes 70S complex dissociation

IF2 function in prokaryotic initiation:

promotes binding and initiation of the tRNA to the small subunit

IF3 function in prokaryotic initiation:

promotes binding of mRNA to the small subunit

eIF1, eIF1a, and eIF3 function in eukaryotic initiation:

bind the small subunit and prevents the large subunit from binding

eIF2 function in eukaryotic initiation:

binds the initiation tRNA to form the ternary complex and is bound to GTP for recruitment to the small subunit

eIF5 function in eukaryotic initiation:

recruited to form the 43S complex (includes eIF1, eIF1a, eIF3, eIF2, tRNA, and GTP)

eIF4 function in eukaryotic initiation:

binds to 5’ cap in mRNA

proteins in eIF4:

A, E, G, B

eIF4E function in eukaryotic initiation:

has cap binding activity

eIF4A function in eukaryotic initiation:

has helicase activity to separate dsRNA

eIF4G function in eukaryotic initiation:

an adapter to bind multiple proteins

eIF4B function in eukaryotic initiation:

recruits eIF4A to mRNA and is required for scanning

_______ is a regulatory step in both initiation and elongation

GTP hydrolysis

prokaryotic elongation factor which corresponds to eukaryotic EF1alpha:

EF-tu

prokaryotic elongation factor which corresponds to eukaryotic EF1beta:

EF-Ts

prokaryotic elongation factor which corresponds to eukaryotic EF2:

EF-G

steps to eukaryotic translation elongation:

1. EF1alpha binds charged tRNA to form the ternary complex

2. EF1alpha is reused and its GDP is swapped for GTP by EF1beta

3. peptide bond between amino acids is facilitated by the ribosomes peptidyl transferase activity

4. translocation of ribosome 5’-3’ facilitated by EF2 bound to GTP

5. deacylated tRNA moves to E site and exits, A site accepts a new charged tRNA, P site contains to peptide chain

prokaryotic release factors:

1. RF1

2. RF2

3. RF3

RF1 recognizes stop codons ____ and ____

UAA and UAG

RF2 recognizes stop codons ____ and ____

UAA and UGA

RF3 function in prokaryotic termination:

a GTP binding protein which facilitates RF1 and RF2 disassembly

Eukaryotic release factors:

1. eRF1

2. eRF3

eRF1 function in eukaryotic translation termination:

recognizes all stop codons

eRF3 function in eukaryotic translation termination:

ribosome dependent GTPase which helps eRF1 recognize the stop codon and release the protein

proteins responsible for subunit disassembly in prokaryotes:

RRF

EF-G

protein responsible for subunit disassembly in eukaryotes:

ABCE1

2 factors which increase the rate of translation:

1. polysome formation-or multiple ribosomes translating a single mRNA at a time

2. interactions to form circular mRNA so when ribosome subunits disassemble, they are near the start codon again and may be reused

interactions which create circular mRNA:

1. PAPBC and poly A tails

2. eIF4G and cap