What is the Kozak consensus sequence associated with?

• A. The sequence context in eukaryotes that helps the ribosome recognize the start codon.
• B. The Shine-Dalgarno sequence in bacteria.
• C. The signal peptide that targets to ER.
• D. The poly-A tail that stabilizes mRNA.

Answer: (A)

The concept tested is how translation begins in eukaryotes and how the sequence around the start codon influences ribosome recognition. The Kozak consensus describes the preferred nucleotides surrounding the AUG start codon that make it more likely for the ribosome to initiate translation at that site. A key feature is having a purine at position -3 and a G at position +4 relative to the A of AUG, with the classic form often summarized as gccRccAUGG (R = a purine). This context helps the scanning ribosome and initiation factors identify the correct start site efficiently, especially in concert with the 5' cap and the poly(A) tail that promote a favorable mRNA conformation for initiation.

Shine-Dalgarno sequences are the bacterial counterpart helping ribosomes bind to the mRNA, not the eukaryotic start-site recognition that the Kozak sequence governs. Signal peptides direct proteins to the endoplasmic reticulum, and the poly-A tail stabilizes mRNA and can influence translation, but it is not about the specific start codon recognition that the Kozak consensus controls.