Chylomicrons contain apolipoprotein B-48, whereas VLDL and LDL contain apolipoprotein B-100. The molecular basis for producing both proteins from a single gene is:
- A Post-transcriptional RNA editing introducing a stop codon ✓
- B Alternative splicing of the primary transcript
- C Proteolytic cleavage of B-100 by intestinal peptidases
- D A separate truncated gene copy on chromosome 2
Correct answer: A. Post-transcriptional RNA editing introducing a stop codon
Explanation
Intestinal cells contain the editing enzyme APOBEC1, which deaminates a single cytidine to uridine in apoB mRNA. This converts a glutamine codon (CAA) to a stop codon (UAA), truncating translation at residue 2153 to yield A-48, about 48 percent of A-100 length. No proteolytic cleavage occurs, splicing is not involved, and both proteins derive from one gene on chromosome 2.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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