Final answer:
The Kozak consensus sequence is a specific nucleotide sequence in eukaryotic mRNA that enhances the efficiency of translation initiation by guiding the ribosome to the correct AUG start codon. It plays a vital role in protein synthesis by ensuring the correct identification of where the ribosome should start translating the mRNA into a protein.
Step-by-step explanation:
The Kozak consensus sequence is a specific sequence of nucleotides in eukaryotic mRNA that defines the optimal context for the initiation of translation. The sequence is denoted by (gcc)gccRccAUG, where 'R' stands for a purine, meaning it can be either 'G' (guanine) or 'A' (adenine). Crucially, the presence of this sequence around the AUG start codon increases the efficiency of translation initiation, as it helps the ribosome to correctly identify the start site for protein synthesis.
The key roles of the sequence include identifying the correct start codon and helping with the proper binding of the ribosomal machinery. This sequence is a guideline rather than a strict rule, but the closer an mRNA's initiating AUG is to this consensus, the more likely it is to be efficiently recognized by the ribosome. In contrast to prokaryotic mRNA, which uses a Shine-Dalgarno sequence to align the ribosome, eukaryotic mRNAs rely on the 7-methylguanosine cap and scanning mechanism for initiation, with the Kozak sequence being a critical element in this process.