Question

Polyribosomes are aggregation of
A.Ribosomes and rRNA
B.Only rRNA
C.Peroxisomes
D.Several ribosomes held together by a string of mRNA

Answer 1

Polyribosomes are also called polysomes which were discovered in 1963 and originally called ergosomes. They are formed during the elongation phase when ribosomes and elongation factors synthesise the encoded polypeptide.

Complete answer:
Let us analyze the options to find out the correct option.

Option A: Ribosomes are protein forming machinery of the cells which with the help of rRNA is involved in the process of translation. Both ribosomes and rRNA are not involved in the formation of polyribosomes. Therefore, this is the incorrect option.

Option B: rRNA is the ribosomal RNA which carries out protein synthesis in ribosomes. They do not form polyribosomes. Therefore, this is the incorrect option.

Option C: Peroxisomes are membrane bound organelle which is found in the cytoplasm of all eukaryotic cells. They are oxidative organelles in which molecular oxygen serves as a substrate from which hydrogen peroxide is formed. They do not form polyribosomes. Therefore, this is the incorrect option.

Option D: Polyribosome is a group of ribosomes bound to an mRNA molecule like beads on a thread. The mRNA is translated into a polypeptide chain by single or multiple ribosomes simultaneously. This group of multiple ribosomes is held together by a string of mRNA forming an aggregate of polyribosomes. Therefore, this is the correct option.

Hence, the correct answer is option (D)

Note: Multiple ribosomes move along the coding region of mRNA forming a polysome. Polysome activity is used to measure level of gene expression by a technique called polysomal profiling.