Question

What is step 3 in POL II initiation (mRNA)?

Answer 1

Stage 3 in POL II initiation involves the formation of an initiation complex on mRNA, where the Shine-Delgarno sequence binds with the small ribosomal subunit, followed by the pairing of the initiator tRNA's anticodon with the start codon, aided by initiation factors.

Step-by-step explanation:

Initiation of Polypeptide Chain in Protein Synthesis

The process of protein synthesis in prokaryotic organisms begins with the initiation phase. Specifically, stage 3 of POL II initiation involves the formation of a functional initiation complex on the mRNA template. During this phase, initiation factors (IFs) facilitate the binding of the small ribosomal subunit to the mRNA.

The Shine-Delgarno sequence of the mRNA binds to a complementary sequence in the 16S rRNA of the 30S subunit. This is followed by the arrival of the initiator tRNA, which carries the amino acid methionine. The anticodon of this charged tRNA pairs with the start codon (AUG) on the mRNA.

Factors IF1 and IF3 assist in this process by ensuring the correct positioning of the tRNA and preventing premature binding of the larger ribosomal subunit. Once the initiator tRNA is properly placed, and the start codon is recognized, the 50S ribosomal subunit associates to complete the formation of the initiation complex, leading to the next phase of protein synthesis, elongation.

Answer 2

Step 3 in POL II initiation (mRNA) is the formation of the initiation complex, involving the small ribosomal subunit, mRNA template, initiation factors, and special initiator tRNA.

Step-by-step explanation:

Step 3 in POL II initiation (mRNA) is the formation of the initiation complex.

This complex consists of the small ribosomal subunit, the mRNA template, initiation factors, and a special initiator tRNA.

The initiator tRNA interacts with the start codon AUG and is charged with the amino acid methionine, which becomes the first amino acid of the polypeptide chain.