1. A group of proteins distributed along inner nuclear membrane form:

a) Nuclear pore

b) Nuclear lamina

c) Nucleosome

d) Nucleotides

 

2. Which nuclear structural element's function is a selective transport?

a) Nuclear lamina

b) Nuclear pore complex

c) Chromatin

d) Nucleolus

2. Before nuclear pore complexes were well understood, it wasunclear whether nuclear proteins diffused passively into thenucleus and accumulated there by binding to residents of thenucleus such as chromosomes, or were actively transported andaccumulated regardless of their affinity for nuclearcomponents.
A classic experiment that addressed this problem used several formsof radioactive nucleoplasmin, which is a large pentameric proteininvolved in chromatin assembly. In this experiment, either theintact protein or the nucleoplasmin heads, tails, or heads with asingle tail were injected into the cytoplasm or into the nucleus offrog oocytes. All forms of nucleoplasmin, except heads, accumulatedin the nucleus when injected in the cytoplasm, and all forms wereretained in the nucleus when injected there.
A. What portion of the nucleoplasmin molecule is responsible forlocalization inthe nucleus?
B. How do these experiments distinguish between active transport,in which a nuclear localization signal triggers transport by thenuclear pore complex, and passive diffusion, in which a bindingsite for a nuclear component allows accumulation in thenucleus?

Nuclear proteins having a molecular mass more than approximately 40 KDa must be actively imported through nuclear pore complexes. What is the name given to the amino acid sequence (located in the protein that needs to be transported) that allows the selective transport of proteins into the nucleus? Name the three important factors that are required for the import of proteins into the nucleus and briefly describe how they function.