Ribosomes are primarily responsible for

• A. Make proteins
• B. Store lipids
• C. Synthesize nucleotides
• D. Regulate cell division

Answer: (A)

Ribosomes function as the cell's protein factories—they translate the genetic message into polypeptide chains. During translation, mRNA provides the sequence of amino acids, which are brought in by transfer RNAs and linked by ribosomal enzymes to build a growing protein. This process can occur freely in the cytosol or on the rough endoplasmic reticulum, determining where the finished protein will go in the cell. Because making proteins is the primary job of ribosomes, they are best described as responsible for protein synthesis.

They do not store lipids—lipid storage occurs in lipid droplets, and lipid synthesis mainly happens in the smooth endoplasmic reticulum. They do not synthesize nucleotides; nucleotide production involves metabolic pathways in the cytosol and mitochondria. They do not regulate cell division; that control comes from cell-cycle regulators like cyclins and kinases.