Question

question 12 proteins that are mainly used inside the cell are synthesized ______. a in the nucleus b on polyribosomes c on rough er d in the nucleoli

Explanation:

• Option A: The nucleus is the control center of the cell, containing DNA, and is not the site of protein synthesis. So A is incorrect.
• Option B: Polyribosomes (free ribosomes) synthesize proteins that are used within the cell. Proteins for internal cell use are made on free polyribosomes in the cytoplasm.
• Option C: Rough ER - bound ribosomes synthesize proteins that are either secreted out of the cell, inserted into the cell membrane, or sent to lysosomes. So proteins for internal cell use are not mainly synthesized here. Thus, C is incorrect.
• Option D: Nucleoli are involved in ribosome subunit production, not protein synthesis. So D is incorrect.

Answer:

B. on polyribosomes