Ques. 1AIPMT 2000
Which of the following ribosomes are engaged in protein synthesis in animal cell?
- Ribosomes of only nucleolus and cytosol
- Ribosomes which occur on nuclear membrane and E.R.
- Ribosomes of only mitochondria and cytosol
- Ribosomes of only cytosol
Answer
(2) Ribosomes which occur on nuclear membrane and E.R.
Solution
As per NCERT, ribosomes attached to the outer surface of the endoplasmic reticulum make it rough ER, which is frequently observed in cells actively involved in protein synthesis and secretion.
⇒ The outer membrane of the nuclear envelope is continuous with the ER and also bears ribosomes.
∴ Ribosomes on the nuclear membrane and ER are engaged in protein synthesis; the nucleolus is only the site of ribosome assembly, not of protein synthesis.
Answer: (2)