Question

A eukaryotic cell is exposed to a chemical that inhibits the 5' capping of pre-mRNA. What is the most likely effect on translation?

• A. Translation will initiate but elongation will be impaired.
• B. Translation will fail to initiate due to improper ribosome binding.
• C. The polyadenylation will not occur.
• D. Splicing of introns will be unaffected.

Hint:

Think of the eukaryotic mRNA modifications as "passports" and "instructions." The 5' cap is the "address label" that tells the ribosome where to bind and start reading. Without this label, the ribosome is lost and cannot begin its job of translation.

Answer 1

The Correct Option is B

Step 1: Concept Summary:
The question concerns the impact of inhibiting 5' cap addition to eukaryotic pre-mRNA on translation. The 5' cap is a modified guanine nucleotide added to the 5' end of mRNA.
Step 2: Detailed Explanation:
The 5' cap's functions in eukaryotes include:

Protection: Prevents mRNA degradation by 5' exonucleases.
Nuclear Export: Facilitates mRNA transport from the nucleus to the cytoplasm.
Translation Initiation: Acts as the ribosome's primary binding site on the mRNA. The cap-binding complex (eIF4F) recognizes the cap, recruiting the 40S ribosomal subunit, a critical step for initiating translation.
Analyzing the options:

(A) Translation will initiate but elongation will be impaired: Incorrect. The cap is essential for initiation, not elongation. Its absence blocks initiation.
(B) Translation will fail to initiate due to improper ribosome binding: Correct. Without the 5' cap, the ribosome cannot bind to the mRNA effectively, preventing translation initiation.
(C) The polyadenylation will not occur: Incorrect. Polyadenylation (poly-A tail addition) at the 3' end is separate from 5' capping, although related. Capping inhibition doesn't directly prevent polyadenylation.
(D) Splicing of introns will be unaffected: Not the most direct effect on translation. While capping influences splicing efficiency for some introns, its primary role is translation initiation. The question focuses on the effect on {translation}.
Step 3: Final Answer:
Inhibiting 5' capping prevents proper ribosome binding to mRNA, leading to translation initiation failure.