Nucleus

Question 1

What is the nuclear lamina made out of?

Answer 1

A mesh of long filament-like proteins called ABC nuclear lamins.

Question 2

Where is the nuclear lamina located?

Answer 2

It is bound to the inner surface of the nuclear envelope

Question 3

What is the name given to nuclei that have mutations in the nuclear lamina?

Answer 3

Progeria

Question 4

What are nuclear speckles?

Answer 4

Subdomains where mRNA slicing factors are highly concentrated.

Question 5

True or False: each cell has about 10 speckles that are stationary.

Answer 5

False. Speckles are numerous (about 50) and can move, grow and shrink depending on cell needs.

Question 6

True or False: the nucleolus is not membrane bound

Answer 6

True.

Question 7

Where does ribosomal assembly occur?

Answer 7

The early stages begin in the nucleolus before being transported to the cytosol for final assembly.

Question 8

What is the purpose of the nuclear matrix?

Answer 8

It is a mesh that serves a structural role for the nucleus, and as a scaffold for anchoring protein factors.

Question 9

What “filament-like” protein lines the inside of the Nuclear Pore Complex?

Answer 9

The FG nucleoporins, made of numerous FG repeats.

Question 10

True or False: only the cytoplasmic side of the NPC has filaments.

Answer 10

True. The nucleoplasm side has a basket instead.

Question 11

How small do molecules have to be to freely pass through the NPC?

Answer 11

Less than 40 kDa. RNA and most proteins have to be selectively imported.

Question 12

Where is nucleoplasmin synthesized?

Answer 12

In the cytosol

Question 13

Explain the difference between a classic NLS and a bipartite NLS.

Answer 13

The classic NLS is a short stretch of basic amino acids, while the bipartite NLS is two short sequences with a 7-10 amino acid spacer.

Question 14

Name the two types of karyopherins (transport receptors)

Answer 14

Importin (into nucleus) and exportin (out of nucleus)

Question 15

How do G-proteins work?

Answer 15

A GTP (3 Ps) holds the protein closed in its active state. When a P is released to become GDP (2 Ps), the protein opens up into its non-active state.

Question 16

True or False: there is a high amount of Ran-GTP in the cytosol.

Answer 16

False. Ran-GTP flows a gradient to accumulate in the nucleus. It is low in the cytosol.

Question 17

What is the role of GTPase Activating Protein (GAP) in the cytosol?

Answer 17

It hydrolyses Ran-GTP into Ran-GDP so it can translocate back into the nucleus.

Question 18

What is the role of Guanine nucleotide Exchange Factor in the nucleus?

Answer 18

It exchanges Ran-GDP for Ran-GTP in the nucleus.

Question 19

True or False: Importin a attaches to the cargo protein to transport it into the nucleus.

Answer 19

True. However, Importin B needs to bind to Importin a in order to transport. It does this by binding to the cytoplasmic filament to open the NPC.

Question 20

What is the role of Ran-GTP?

Answer 20

Once the cargo receptor complex passes into the NCP, it attaches to Importin B in order to release the cargo from the NCP and disassemble it.

Question 21

Name the two proteins involved in regulating the Ran-GTP gradient.

Answer 21

RCC1 and Ran-GAP1

Question 22

How does exportin and Ran-GTP work together to transport proteins?

Answer 22

Exportin targets proteins in the nucleus with NES sequences, and the Ran-GTP binds to this complex in order to move it down the Ran-GTP gradient out of the nucleus.