Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologymediummcq1 pt

Soon after RNA polymerase II begins transcribing a eukaryotic gene, enzymes add a modified guanine nucleotide to the 5' end of the growing transcript. What does this modification accomplish?

A.It shields the transcript from exonuclease attack and later helps the ribosome recognize the mRNA
B.It stitches completed exons together once the spliceosome removes each intron
C.It marks the transcript for destruction unless the gene is actively needed
D.It converts the single-stranded transcript into a double helix ready for export

Explanation

Core Concept

The 7-methylguanosine cap is joined to the first transcribed nucleotide in an unusual reverse linkage. It blocks exonucleases that otherwise chew inward from the 5' end, extending mRNA lifetime. Initiation factors also bind the cap to recruit the small ribosomal subunit when translation begins.

Correct Answer

AIt shields the transcript from exonuclease attack and later helps the ribosome recognize the mRNA

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