Which statement is true regarding ribosomes during protein synthesis?

Which statement is true regarding ribosomes during protein synthesis?

• A. During protein synthesis, only two sites of a ribosome can be occupied at a time
• B. A ribosome binds only one tRNA at all times
• C. rRNA does not contain the catalytic activity that joins amino acids together
• D. Ribosomes are large RNA structures composed solely of rRNA

Answer: (A)

The statement that during protein synthesis, only two sites of a ribosome can be occupied at a time is accurate. Ribosomes are composed of several sites, primarily the A (aminoacyl), P (peptidyl), and E (exit) sites. At any given moment during protein synthesis, the ribosome can hold two tRNA molecules at the A and P sites, allowing it to facilitate the formation of peptide bonds between amino acids. This arrangement is crucial for the process of translation, as the ribosome moves along the mRNA sequence, recruiting tRNAs that correspond to the codons being read. In contrast, the other statements do not hold true during protein synthesis. For example, a ribosome does not bind only one tRNA at all times—multiple tRNAs can interact with the ribosome during the process (notably in the A and P sites). Additionally, ribosomal RNA (rRNA) does indeed have catalytic activity as it is involved in forming peptide bonds between amino acids. Furthermore, while ribosomes contain rRNA, they are not composed solely of rRNA; they also contain proteins, which are essential for their structure and function.

The statement that during protein synthesis, only two sites of a ribosome can be occupied at a time is accurate. Ribosomes are composed of several sites, primarily the A (aminoacyl), P (peptidyl), and E (exit) sites. At any given moment during protein synthesis, the ribosome can hold two tRNA molecules at the A and P sites, allowing it to facilitate the formation of peptide bonds between amino acids. This arrangement is crucial for the process of translation, as the ribosome moves along the mRNA sequence, recruiting tRNAs that correspond to the codons being read.

In contrast, the other statements do not hold true during protein synthesis. For example, a ribosome does not bind only one tRNA at all times—multiple tRNAs can interact with the ribosome during the process (notably in the A and P sites). Additionally, ribosomal RNA (rRNA) does indeed have catalytic activity as it is involved in forming peptide bonds between amino acids. Furthermore, while ribosomes contain rRNA, they are not composed solely of rRNA; they also contain proteins, which are essential for their structure and function.