Ribosomes are described as what?

• A. Energy producers
• B. Protein builders made up of RNA
• C. Membrane-bound sacs
• D. Genetic material

Answer: (B)

Ribosomes are protein-synthesis machines made mostly of RNA and protein. They translate messenger RNA into a polypeptide chain, with the RNA component (rRNA) playing a central catalytic role in forming peptide bonds. They are not energy producers—the job of generating energy lies with mitochondria (and chloroplasts in plants). They aren’t membrane-bound sacs, though some ribosomes attach to the rough endoplasmic reticulum; the ribosome itself is a small particle, not a membrane-bound compartment. They aren’t genetic material—the cell’s genetic material is DNA (and, in some contexts, RNA as a messenger), but ribosomes don’t carry the genome.