Question

What is polyribosome?
A. Association of several ribosomes on a single mRNA molecule is called a polyribosome.
B. Association of several mRNAs on a single ribosome molecule is called a polyribosome.
C. Association of several ribosomes.
D. Association of several deoxy ribosomes.

Answer 1

Hint: A polyribosome or polysome is a bead on a thread-like structure that helps in simultaneous translation of mRNA segments. They have a significant role in the translation process. They are also called ribosome complexes.

Complete answer: A polyribosome forms a key unit of translation. Protein synthesis occurs through two vital processes called transcription and translation. Transcription is the process through which a complementary sequence of DNA template is made which is called the messenger RNA or mRNA. The mRNA consists of the codons required for the production of amino acids. Amino acids are structural units of proteins and hence are provided by mRNA. The code on mRNA is read by tRNA. The tRNA forms a translation complex with ribosomes. These complexes read the 3 base codons on mRNA and form amino acids. These amino acids are then arranged in rows and are modified to form proteins.
Sometimes many ribosomes units come together to form a string. This string of ribosomes read the mRNA simultaneously forming the same protein. This string of ribosomes is called polysome or polyribosome. Hence, we can define a polyribosome as an association of several ribosomes that read on a single mRNA molecule. It is not an association of mRNA units.
So, option A is the correct answer.

Note: The polysome activity can be used to indicate the measure of the level of gene expression. This can be done through a technique called polysomal profiling. Electron microscopy can be used to visualize the polyribosomes. In prokaryotes, double-row structures are found as polyribosomes.