Structure and Function of Ribosomes

What is the key role of ribosomes in protein synthesis?

(a) Ribosomes consist mainly of proteins rather than rRNA molecules.

(b) The large subunit of ribosomes is responsible for catalyzing peptide bond formation.

(c) The catalytic site for peptide bond formation is primarily formed from rRNA.

(d) Ribosome subunits remain permanently assembled until degraded by the proteasome.

Answer:

The correct statement is: (c) The catalytic site for peptide bond formation is primarily formed from rRNA.

Ribosomal ribonucleic acid (rRNA) together with proteins is the major component of the ribosome. rRNA is essential for protein synthesis in all living organisms. Ribosomes contain two major rRNAs (and about 50 proteins) that form two ribosomal subunits, the large one and the small one. The large subunit rRNA has a function of ribozyme: catalyzes peptide bond formation.

Final Answer:

The true statement about ribosomes is that the catalytic site for peptide bond formation is predominantly formed from rRNA. Ribosomes are composed of both rRNA and proteins where rRNA has a crucial role in catalyzing peptide bond formation between amino acids.

Explanation:

The correct statement regarding ribosomes is option (c) - The catalytic site for peptide bond formation is formed primarily from an rRNA. Ribosomal RNA (rRNA) constitutes a significant proportion of the ribosome and plays a critical role in protein synthesis by catalyzing the formation of peptide bonds between two aligned amino acids. This is done at the catalytic site, which is primarily formed by rRNA.

Regarding the other options, (a) is not fully accurate because the number of rRNA molecules does not necessarily greatly exceed the number of protein molecules in a ribosome. (b) While the ribosome's large subunit does play a role in protein translation, it is the small subunit that is primarily responsible for binding the mRNA.

Finally, in reference to option (d), the large and small subunits of a ribosome can and do disassemble and reassemble as needed for protein synthesis. They are not in a permanent state of assembly until degraded by the proteasome.