Question

What is a polyribosome?

A. a ribosome that is in the process of translating an mRNA into a polypeptide
B. a ribosome translating an mRNA molecule that encodes a membrane-embedded protein
C. a cluster of ribosomes simultaneously translating the same mRNA, but positioned at different sites along the mRNA
D. a mutant ribosome that contains additional ribosomal subunits
E. a ribosome translating a polycistronic mRNA molecule

Answer 1

A polyribosome is a structure where several ribosomes translate the same mRNA simultaneously, vastly improving protein synthesis efficiency. It occurs in both prokaryotic and eukaryotic cells, with ribosomes dissociating at the end of translation.

Step-by-step explanation:

A polyribosome is a complex formed when multiple ribosomes are simultaneously translating the same mRNA molecule. Each of these ribosomes reads the mRNA from 5' to 3' direction, creating multiple copies of the polypeptide chain that the mRNA encodes. This process enhances the efficiency of protein synthesis since many ribosomes work on a single mRNA strand, thereby increasing the rate of protein production.

In prokaryotic cells, transcription and translation can occur concurrently because they both take place in the cytoplasm, and the RNA transcript does not require processing. In contrast, eukaryotic cells must complete transcription in the nucleus and finish modifying the mRNA before it can be exported to the cytoplasm for translation by polyribosomes.

At the end of translation, ribosomes dissociate into their large and small subunits, which can later reassemble when a new round of translation initiates.