Question

What structure in the nuclear envelope of eukaryotic cells allows most proteins to cross, from the cytoplasm into the nucleoplasm, without being unfolded and refolded by chaperones?

A. the smooth endoplasmic reticulum

B. the Golgi apparatus

C. the rough endoplasmic reticulum

D. the nucleoli

E. the nuclear pores

Answer 1

The question speaks about the scenario where the transpot of proteins is into the nucleoplasm rather than out of it. Nulear envelop is a selectively permeable membrane and allows the entry of only limited number of molecules. This is to ensure that the DNA is well protected and is prevented from harm. Let's go through the options one by one to find the answer:

1)Smooth endoplasmic reticulum: smooth endoplasmic retiulum is an organelle that is involved in variety of metabolic processes. It plays a key role in the synthesis of lipids, phospholipids and steroids. Since it's major role is in synthesis, not in transpot, the option is not the answer.

2) The Golgi apparatus: This organelle is membrane bound and plays a major role in secretory pathway. The organelle is responsible for sorting and packaging the secreted proteins into vesicles for transport.

3) Rough endoplasmic reticulum: Rough endoplasmic reticulum functions in the synthesis of proteins. It is associated with ribosomes that are responsible for the synthesis. The organelle is continuous with the nuclear envelop.

4) The nucleoli: The nucleoli is the one of the largest part of the nucleus and functions in the synthesis of ribosomal subunits.

5) The nuclear pores: The nuclear pores are situated in the nuclear envelop and is laden with proteins. It is responsible for regulating the transport of molecule to and from the nucleus and the cytosplasm. It is this organelle that allows the proteins into the nucleoplasm from the cytoplasm. The answer thus is e)the nuclear pores.