Question

Which end of a new mRNA transcript gets a cap during processing in the nucleus?

a. the top
b. the bottom
c. the 3' end
d. the 5' end

Answer 1

d. the 5' end

Step-by-step explanation:

Capping is a co-transcriptional modification made to RNA in the nucleus after the first 25–30 nts are incorporated into the nascent transcript, which is synthetized in the 5' ---> 3' direction.

The cap consists of a methylated guanosine nucleotide added to the 5' end of the new mRNA transcript, and is important for several processes, which include:

1. Protection of the mRNA from the attack of phosphatases and nucleases.
2. Splicing of mRNA in the nucleus.
3. Nuclear export of the mRNA to the cytoplasm.
4. Cap-dependent protein synthesis.