Lecture 11: intracellular compartments and protein sorting

Question 1

What is the plasma membrane?

Answer 1

• outer boundary of cells

- protective barrier has transporters and signaling

Question 2

What is the nucleus?

Answer 2

• contains the genome

- principal site for RNA and DNA synthesis

Question 3

Where does intermediary metabolism occur?

Answer 3

cytoplasm

Question 4

Where does protein synthesis, lipid synthesis, protein folding, and storage of calcium?

Answer 4

• endoplasmic reticulum

Question 5

What are the three topological divisions of the cell?

Answer 5

• nucleus and cytosol
• organelles in secretory and endocytic pathways
• mitochondria

Question 6

How do cells communicate with other cells and the exterior?

Answer 6

• budding and fusion

Question 7

Transport between what two structures requires gated transport?

Answer 7

• nucleus and cytosol

Question 8

What is transmembrane transport?

Answer 8

• transport of specific proteins from cytosol across organelle membrane via protein translocators

Question 9

What is vesicular transport?

Answer 9

membrane-enclosed transport intermediates move proteins between various compartments via vesicles

Question 10

What is a signal sequence and why is it important?

Answer 10

• signal sequence is used to direct the movement of a peptide to certain areas.
• it is located on N or C terminus or within the protein sequence

Question 11

What describes the nuclear transport?

Answer 11

• gated
• bidirectional
• selective

Question 12

What proteins are imported from the cytosol into the nucleus?

Answer 12

• histones
• RNA/DNA pol
• topoisomerases
• gene regulatory proteins

Question 13

Which proteins are synthesized in the nucleus and transported to the cytosol?

Answer 13

• tRNA

- mRNA

Question 14

What are nuclear pore complexes?

Answer 14

• 30 different nucleoporins arrange to provide passive and faciliated transport of molecules

Question 15

How is transport facilitated by nuclearporins?

Answer 15

• binding of particles to fibrils extending from the nuclear pore complex

Question 16

What size molecules enter the nucleus via free diffusion?

Answer 16

• small molecules

Question 17

What size molecules enter the nucleus via active transport?

Answer 17

• large molecules

Question 18

What is a nuclear localization signal (NLS)

Answer 18

• sorting signal that directs molecules to nucleus

- positively charged lysine and arginine

Question 19

What is the effect of activating NLS, nuclear localization signals?

Answer 19

• selective import of proteins into the nucleus

Question 20

What are nuclear import receptors structure and where do they bind at?

Answer 20

• soluble cytosolic proteins that bind to NLS

- also bind to nuclear pore complexes on fibrils extending into the cytoplasm

Question 21

Where do nuclear import receptors bind on nuclear pore complexes?

Answer 21

• phenylalanine glycine repeats (FG)

Question 22

What mechanics are used for nuclear export and what is the sequence these proteins do this in?

Answer 22

• nuclear export signals and receptors

- bind, dissociate and re-bind

Question 23

What are the effects of Ran-GTP binding?

Answer 23

1. allows cargo delivery from cytosol into the nucleus by binding to the import receptor and cargo protein complex
2. allows formation and migration of export signal protein to the cytosol from the nucleus. Hydrolysis of GTP allows off-loading of the cargo in the cytosol

Question 24

What happens if proteins contain both the nuclear export signal and the nuclear localization signal?

Answer 24

• protein is shuttled back and forth between the nucleus and cytosol

Question 25

What are the mechanisms that control the cargo transport in or out of the nucleus?

Answer 25

• phosphorylation
• proteolysis
• inhibitory protein binding

Question 26

If cholesterol is high, what is the following pathway and result?

Answer 26

• cholesterol binds with SCAP blocking SREBP and blocking biosynthesis of cholesterol
• cholesterol production is reduced

Question 27

If cholesterol is low what is the resulting pathway and result?

Answer 27

• SCAP and SREBP are not bound/blocked which lead to cleavage at site 1 and 2 proteaese. this releases a factor that binds and induces cholesterol biosynthesis enzymes.
• results in production of cholesterol.