Ribosome Structure and Translation

What is the primary function of eRF1 in translation termination?

What occurs if an incorrect amino acid is incorporated at the P site?

Which mechanism does the ribosome utilize to move tRNA between sites?

What is the role of eRF3 during translation termination?

Which technique is NOT used to determine the 3D structure of a protein?

What does the 's' in 70s ribosome indicate?

Which tRNA binding site is responsible for holding the newly arrived aminoacylated tRNA?

What protein facilitates the initial binding of the mRNA 5’ CAP during the formation of the pre-initiation complex?

What happens when the A site of the ribosome is occupied by a correct tRNA?

Which factor is responsible for bringing the charged tRNA to the A site?

What initiates the formation of the 48s initiation complex during eukaryotic translation?

What is the role of the peptidyl-transferase center in the ribosome?

Which factor is removed by eIF5 during the transition to the 80s initiation complex?

Ribosome Structure and Function

Prokaryotic ribosomes = 70S, composed of 50S and 30S subunits.
Eukaryotic ribosomes = 80S, composed of 60S and 40S subunits.
"s" represents sedimentation rate, not a simple addition.
Ribosomes have sites for RNA binding (1 mRNA, 3 tRNA).
- A site: Aminoacyl-tRNA
- P site: Peptidyl-tRNA
- E site: Exit site

Eukaryotic Translation Initiation

mRNA exits nucleus to cytoplasm.
eIF4 proteins (A/E/G) bind the 5' cap.
eIF1, eIF2, and eIF3 join with the 40S subunit and Met-tRNA.
43S pre-initiation complex forms (eIF1, eIF2, eIF3, 40S subunit, Met-tRNA).
48S initiation complex forms (43S complex + eIF4A/E/G + mRNA at 5'UTR).
Complex scans for the start codon (AUG) in the mRNA.
Once AUG is at the P site, eIF5 releases initiation factors.
60S subunit joins 40S, forming 80S initiation complex.

Elongation

Charged tRNA enters the A site via EF-1α-GTP.
Kinetic proofreading:
- Correct tRNA: GTP hydrolyzed rapidly, EF-1α detaches.
- Incorrect tRNA: GTP hydrolyzed slowly, tRNA and EF-1α detach.
Peptide bond forms between amino acids in A and P sites (peptidyl transferase center, rRNA).
Ribosome moves (ratchet mechanism): P site tRNA to E site, A site tRNA to P site.
Large subunit moves first, followed by the small subunit.

Termination

Stop codon reached.
eRF1 recognizes stop codon.
eRF3 facilitates polypeptide release (GTP dependent).
Proofreading function:
- Incorrect tRNA in P site: eRF1 triggers termination despite incorrect amino acid.
- Incorrect amino acid: More changes and incorrect amino acid inclusion.

Techniques for studying protein structure and interactions

FLIM-FRET: Measures distances with fluorescent probes.
Other techniques for determining protein structure: Circular dichroism, NMR, electron microscopy, X-ray crystallography.

This quiz explores the structure and function of ribosomes, focusing on both prokaryotic and eukaryotic types. It also covers the initiation and elongation phases of eukaryotic translation, detailing the roles of various initiation factors and tRNA binding sites. Test your knowledge on the intricate process of protein synthesis!