Cell biology fundamentals – ribosomal function: Within a living cell, what is the primary physiological function carried out by ribosomes during gene expression and growth?

Introduction / Context:
Ribosomes are central to the flow of genetic information from nucleic acids to functional macromolecules. Knowing exactly what ribosomes do helps clarify where energy generation, DNA replication, and metabolism occur within cellular architecture.

Given Data / Assumptions:

• Cells contain specialized machinery: ribosomes (translation), ATP synthase (energy), polymerases (replication/transcription), and metabolic enzymes (fermentation).
• Question asks specifically for the principal role of ribosomes.
• Both prokaryotes (70S) and eukaryotes (80S cytosolic; 70S in mitochondria/chloroplasts) possess ribosomes with the same core function.

Concept / Approach:
Ribosomes decode mRNA codons and catalyze peptide bond formation, producing polypeptides that fold into functional proteins. The small subunit binds mRNA and ensures codon–anticodon pairing with tRNA; the large subunit’s peptidyl transferase activity forms peptide bonds. While ATP is required for many cellular processes, ATP synthesis is not a ribosomal function; fermentation occurs via cytosolic enzymes; DNA replication is executed by DNA polymerases in distinct compartments.

Step-by-Step Solution:
Map each option to its correct cellular machine. Recognize that translation is uniquely the job of ribosomes. Exclude energy production and DNA replication activities. Select protein synthesis as the correct answer.

Verification / Alternative check:
Structural biology shows tRNAs moving from A to P to E sites on the ribosome while nascent chains exit via the ribosomal tunnel—direct evidence of protein synthesis.

Why Other Options Are Wrong:
ATP production is primarily mitochondrial (ATP synthase) or via substrate-level phosphorylation; fermentation uses specific metabolic enzymes; DNA replication uses DNA polymerases and accessory factors, not ribosomes.

Common Pitfalls:
Assuming “all of these” because ribosomes are abundant; abundance does not equal multifunctionality.

Final Answer:
To synthesize proteins by translating mRNA.