Question

1. What are the eukaryotic translation termination codons? How do these codons function to terminate translation?

A.

AGA, AGG, UGA. Release factor eRF binds to these codons, blocks translation, and stimulates hydrolysis of the newly formed polypeptide chain attached to the t-RNA located at the P-site

B.

UAA, UAG, UGA. Release factor eRF binds to these codons, blocks translation, and stimulates hydrolysis of the newly formed polypeptide chain attached to the t-RNA located at the P-site

C.

UAA, UAG, UGA. No release factor is needed. Lack of a t-RNA in the A-site causes a block in translation, thereby stimulating hydrolysis of the newly formed polypeptide chain attached to the t-RNA located at the P-site

D.

UAA, UAG, UGA. Three release factors bind to these codons, block translation, and stimulates hydrolysis of the newly formed polypeptide chain attached to the t-RNA located at the P-site

E.

UUA, UAG, UGG. Two release factors bind to these codons, block translation, and stimulates hydrolysis of the newly formed polypeptide chain attached to the t-RNA located at the P-site

2. What is the mechanism of action of Tetracycline?

A.

Blocks the “A” site

B.

Blocks the peptidyl transferase of 80S eukaryotic ribosome

C.

Blocks peptidyl transferase of bacteria

D.

Blocks the “P” site

E.

Misreading of the genetic frames

3.

What is the mechanism of action of Streptomycin?

A.

Blocks the peptidyl transferase of 80S eukaryotic ribosome

B.

Blocks the “A” site

C.

Blocks peptidyl transferase of bacteria

D.

Blocks the “P” site

E.

Misreading of the genetic frames

Answer 1

1. The correct answer is option D i.e. UAA, UAG, and UGA. Three release factors bind to these codons, block translation, and stimulates hydrolysis of the newly formed polypeptide chain attached to the t-RNA located at the P-site.

Eukaryotic termination occurs when ribosome encounters stop codon (UAG, UAA, UGA) and hydrolyzes peptide bond between tRNA in the p-site and growing peptide chain. Stop codons do not bind to tRNA but rather to eukaryotic release factor 1 (eRF1), a factor rebound to eRF3 and GTP. All three of these are necessary as eRF3 induces GTP hydrolysis, which facilitates a conformational change in eRF1, allowing it to hydrolyze the polypeptide chain.

2. The correct answer is option A i.e. blocks the "A" site. Tetracycline inhibits protein synthesis by blocking the attachment of charged aminoacyl-tRNA to the A site on the ribosome.

3. The correct answer is option E i.e. misreading of the genetic frames. Streptomycin is an aminoglycosides that bind to sites on the 30S ribosomal subunit and cause the misreading of genetic code that leads to abnormal proteins; thus they inhibit peptide initiation and elongation.