Peptide Bonds and Protein Primary Structure (1A) Practice Test

Researchers examined a mitochondrial matrix enzyme whose coding sequence contains a Lys-Lys-Lys stretch. They introduced a synonymous mutation that preserved the amino acid sequence but altered codon usage to rare Lys codons. In isolated mitochondria, the mutant mRNA produced less full-length protein and more ribosome-associated intermediates, despite unchanged mRNA abundance. Protease protection assays indicated intermediates remained bound to the ribosome. Which interpretation is most consistent with a defect in peptide bond formation affecting primary structure synthesis?

(Assume no changes to targeting sequence or mRNA secondary structure.)

A synthetic biology group expressed a peptide containing multiple consecutive prolines in mammalian cells. Ribosome profiling showed pauses at the polyproline region that were relieved by overexpressing a specialized elongation factor. Which statement is most consistent with the idea that primary structure extension depends on efficient peptide bond formation at difficult sequences?

(Assume initiation and mRNA levels are unchanged.)