During the elongation phase of translation, how many tRNA molecules are held in the ribosome at the same time?

• A. One
• B. Four
• C. Two
• D. Three

Answer: (C)

Verified step by step guidance

1. Understand the process of translation: Translation is the process by which ribosomes synthesize proteins using mRNA as a template. It consists of three phases: initiation, elongation, and termination.
2. Focus on the elongation phase: During elongation, the ribosome facilitates the addition of amino acids to the growing polypeptide chain by matching tRNA molecules carrying amino acids to the codons on the mRNA.
3. Learn about the ribosome's structure: The ribosome has three binding sites for tRNA molecules: the A site (aminoacyl site), P site (peptidyl site), and E site (exit site). These sites play distinct roles in translation.
4. Determine how many tRNA molecules are held during elongation: At any given time during elongation, the ribosome holds two tRNA molecules simultaneously. One tRNA is in the P site, carrying the growing polypeptide chain, while another tRNA is in the A site, bringing the next amino acid to be added.
5. Understand the movement of tRNA: After the amino acid is added to the polypeptide chain, the tRNA in the P site moves to the E site and exits the ribosome, while the tRNA in the A site shifts to the P site, making room for a new tRNA to enter the A site.