Zaidi Lecture 1 9/17

Question 1

What are the 3 topological categories?

Answer 1

1. nucleus and cytosol- communicate through the nuclear pore complex
2. organelles in the secretory and endocytic pathways
3. mitochondria

Question 2

How do the organelles in the secretory and endocytic pathways communicate with each other and with the cell exterior?

Answer 2

through budding and fusion

Question 3

Define gated transport

Answer 3

between the nucleus and the cytosol through the nuclear pore complex
uses active transport and diffusion

Question 4

Define transmembrane transport

Answer 4

protein trans locators transport proteins from the cytosol across the membrane

Question 5

Define vesicular transport

Answer 5

uses vesicles between the compartments

Question 6

What is a sorting signal?

Answer 6

A stretch of 15-60 amino acids at the N or C terminus that help in protein sorting

Question 7

what is the signal peptidase

Answer 7

can remove the signals after the protein reaches its final destination—trap

Question 8

How are the signal sequences recognized?

Answer 8

complementary receptors

Question 9

When importing into the nucleus, which signal is needed?

Answer 9

A lot of lysines and arginine

Question 10

When importing a cell into the mitochondria, which signal is needed?

Answer 10

combo of positive charges and hydrophobic amino acids

Question 11

When importing a cell into the ER, what signal sequence is needed?

Answer 11

hydrophobic amino acids

Question 12

When returning a protein into the ER, what signal sequence is needed?

Answer 12

KDEL (lys, asp, glu, leu)

Question 13

Describe nuclear transport

Answer 13

gated
bidirectional
selective

Question 14

Which proteins are imported into the nucleus from the cytosol?

Answer 14

histones, DNA and RNA polymerases, topoisomerase, etc

Question 15

Which proteins are exported from the nucleus to the cytosol?

Answer 15

tRNA and mRNA molecules

Question 16

Describe NPCs

Answer 16

• in nuclear envelop
• 30+ proteins (nucleoporins)
• basket like (octagon)
• both directions
• passive diffusion of small molecules and facilitated transport
• transport via binding to fibrils- have a FG repeat that allows for import receptors to bind

Question 17

What are NLS?

Answer 17

sorting signals that take molecules to the nucleus (Lys and Arg)
selective import

Question 18

How are the NLS located?

Answer 18

nuclear import receptors

Question 19

What are the steps of nuclear import?

Answer 19

1. NLS is recognized by NIRs
2. NIR bind to NLS and then that complex binds to the NPC proteins that are on the fibrils via FG repeats
3. receptor travels through the pore complex with the help of Ran-G(D)P
4. cargo is released in the nucleus when the GTP is added to the Ran

Question 20

What are the steps of nuclear export?

Answer 20

1. NES (nuclear export signals) on molecules that need to leave
2. NER bonds to the cargo present
3. Ran GTP exits with the molecule and the dephospho rylation releases the package

Question 21

What is a protein considered if the rate of import is greater than the export?

Answer 21

a nuclear protein