Definition check: What is a polysome (polyribosome), and which cellular process is it most directly associated with?

Introduction:
A polysome—also called a polyribosome—is a hallmark structure in cells actively translating mRNA. Multiple ribosomes attach to a single mRNA, each making a copy of the encoded polypeptide, thereby boosting protein output. Understanding polysomes clarifies how cells increase translational efficiency and regulate gene expression post-transcriptionally.

Given Data / Assumptions:

• Ribosomes translate mRNA into protein.
• mRNA can be engaged by more than one ribosome at a time.
• Translation proceeds 5′→3′ along mRNA, producing N→C polypeptide chains.

Concept / Approach:
In a polysome, ribosomes are spaced along an mRNA so that as one ribosome clears the start region, additional ribosomes can initiate behind it. This parallelization increases the rate of protein production per mRNA molecule. Electron micrographs and sucrose gradients reveal characteristic polysome profiles correlating with translational activity. Polysomes are therefore not involved in DNA or lipid synthesis directly; they are dedicated machineries for protein synthesis.

Step-by-Step Solution:

Verification / Alternative check:
Polysome profiling separates monosomes from polysomes; increases in polysome fractions indicate enhanced protein synthesis, whereas stress conditions shift ribosomes to monosomes or free subunits.

Why Other Options Are Wrong:

• DNA or lipid synthesis: mediated by polymerases or metabolic enzymes, not ribosomes.
• All of the above/storage granule: mischaracterize the structure and function of polysomes.

Common Pitfalls:
Assuming one ribosome per mRNA at all times; in fast-growing cells, most productive mRNAs are engaged in polysomes for high output.

Final Answer:
An active site of protein synthesis