What distinguishes anabolic from catabolic pathways, and which is exemplified by protein synthesis?

• A. Anabolic pathways break down molecules; catabolic build up molecules; protein synthesis is catabolic.
• B. Anabolic pathways build complex molecules; catabolic pathways break down molecules; protein synthesis is anabolic.
• C. Both primarily involve energy transfer, not synthesis; protein synthesis is neither.
• D. Anabolic and catabolic are the same; protein synthesis can be both.

Answer: (B)

Anabolic pathways build complex molecules from smaller ones, using energy to form new bonds, while catabolic pathways break down complex molecules into simpler ones and release energy. Protein synthesis is an anabolic process because it assembles amino acids into a polypeptide chain to make a protein, a buildup in size and complexity that requires energy input (amino acids are activated with ATP, and peptide bond formation and ribosome movement use GTP). So protein synthesis exemplifies anabolism.

The alternative descriptions misstate the direction of the processes or deny synthesis altogether: breaking down molecules is catabolic, not anabolic; protein synthesis clearly involves building a larger molecule and consuming energy.