Bacterial protein synthesis — identifying active translation sites In prokaryotic cell biology, which cytological structure in a bacterium is a clear indicator that active protein synthesis (translation) is occurring?

Introduction:
In microbiology, recognizing where and how proteins are made inside bacterial cells is essential. Translation is the process by which ribosomes read messenger RNA (mRNA) and synthesize polypeptides. A hallmark of vigorous translation is the presence of polysomes (also called polyribosomes), visible by electron microscopy or detected biochemically as ribosome–mRNA complexes.

Given Data / Assumptions:

• Bacteria translate proteins using 70S ribosomes (50S + 30S subunits).
• During active translation, many ribosomes can bind a single mRNA simultaneously.
• Other cellular structures (chromosome, flagellum, membranes) may be present regardless of translation activity.

Concept / Approach:

A polysome forms when multiple ribosomes initiate on an mRNA and elongate concurrently. This arrangement boosts protein output and is a direct indicator of translation in progress. In bacteria, transcription and translation are often coupled, further enhancing polysome formation near the nucleoid.

Step-by-Step Solution:

Verification / Alternative check:

Polysome profiling (sucrose gradients) separates heavy polysomes from monosomes; increased polysome fractions correlate with higher translation rates. Electron micrographs classically show “beads-on-a-string” ribosome arrays on an mRNA.

Why Other Options Are Wrong:

Chromosome (nucleoid) stores genetic information but is not proof of translation at a given moment. The membrane and flagellum are not markers of translation. Inclusion bodies are storage or aggregated proteins, not necessarily active synthesis sites.

Common Pitfalls:

Confusing ribosome abundance with active translation; free ribosomes may be idle. Only polysome engagement with mRNA confirms active protein synthesis.

Final Answer:

A polysome (polyribosome) composed of multiple ribosomes on one mRNA