Question

Protein synthesis starts at ______________.

Group of answer choices
a.the 5' terminus of mRNA
b.the start codon
c.alanine
d.the carboxy terminus
e.the promoter

Answer 1

Protein synthesis begins at the AUG start codon on mRNA, where an initiator tRNA, complementing this codon, initiates the translation process with a methionine residue.Protein synthesis starts at the start codon.

Step-by-step explanation:

Protein synthesis starts at the start codon.

This is specifically, the AUG codon on mRNA, which is near the 5' end of the mRNA. The AUG codon not only encodes the amino acid methionine but also signals the beginning of the translation process. The initiation complex in protein synthesis includes the small ribosomal subunit, the mRNA template, initiation factors, and the initiator tRNA, which in prokaryotes is called tRNAMet and in eukaryotes, tRNAi.

This initiator tRNA carries an anticodon complementary to the AUG start codon and a methionine residue—the first amino acid incorporated into the nascent polypeptide chain. Furthermore, the mRNA must be properly prepared in the nucleus with a 5' capping before it is translated in the cytoplasm. This cap is a 7-methylguanosine cap which protects the mRNA from degradation and aids in the initiation of translation by the ribosome.