Viruses lack most metabolic machinery; they cannot generate energy or synthesize what key macromolecule on their own?

Introduction:
Unlike cells, viruses are metabolically inert outside a host. They depend on the host’s systems for both energy and biosynthesis. A classic teaching point is the inability of viruses to make their own proteins without hijacking host ribosomes.

Given Data / Assumptions:

• Viruses lack ribosomes and translation factors.
• They require host cell machinery to synthesize viral proteins.
• Options include various molecules and an overbroad “all of these.”

Concept / Approach:
Protein synthesis requires ribosomes, tRNAs, initiation/elongation/termination factors, and aminoacyl-tRNA synthetases. Viruses do not encode complete translation systems; therefore, they cannot synthesize proteins independently. While they also lack metabolic pathways for carbohydrate or alcohol synthesis, the most precise, universally emphasized limitation is protein synthesis.

Step-by-Step Solution:
Identify the universally cited deficit: absence of ribosomes. Relate this to protein synthesis dependency on the host. Choose “protein” as the key macromolecule viruses cannot synthesize alone.

Verification / Alternative check:
Laboratory cultivation always requires living cells because viral gene expression and protein production occur on host translational machinery.

Why Other Options Are Wrong:

• Carbohydrate / Alcohol / Cholesterol: While viruses do not conduct these metabolic syntheses, exam convention highlights protein synthesis as the defining limitation.
• All of these: Overbroad and less precise than the canonical teaching point.

Common Pitfalls:
Assuming “all of these” is always safest; targeted knowledge about ribosome absence makes “protein” the best answer.

Final Answer:
Viruses cannot synthesize protein without host machinery.