Intracellular Compartments And Protein Sorting I

Question 1

What is the principal site of DNA and RNA synthesis?

Answer 1

Nucleus

Question 2

What does the cytoplasm consist of?

Answer 2

Cytosol and cytoplasmic organelles

Question 3

What is the site of protein synthesis, lipid synthesis, protein folding and storage of calcium?

Answer 3

Endoplasmic reticulum

Question 4

Where is the site on which post-translational changes on proteins and lipids occur?

Answer 4

Golgi apparatus

Question 5

What is the site of ATP production, signaling, cell differentiation and death?

Answer 5

Mitochondria

Question 6

What organelle contains digestive enzymes that degrade organelles and biomolecules?

Answer 6

Lysosomes

Question 7

What organelle is a small vesicular compartment that contains enzymes used in oxidative reactions?

Answer 7

Peroxisomes

Question 8

What are the three topological categories of the cell?

Answer 8

Nucleus and cytosol

Organelles

Mitochondria

Question 9

How do the lumen of the nucleus, cytosol, etc. communicate with each other and with the cell exterior?

Answer 9

Membrane budding and fusion.

Question 10

What is gated transport?

Answer 10

Transport between the nucleus and cytosol through nuclear pore complexes.

Question 11

What is invovled in transmembrane transport?

Answer 11

Membrane protein translocators directly transport specific proteins from cytosol across an organelle membrane.

Question 12

What is involved in vesicular transport?

Answer 12

Membrane-closed transport intermediates move proteins between various compartments via vesicles.

Question 13

Where are protein sorting signals localized?

Answer 13

On N or C terminus or within protein sequences.

Question 14

What enzyme may remov a signal after a protein reaches its final destination?

Answer 14

Signal peptidase

Question 15

What are signal sequences necssary for?

Answer 15

Protein targeting.

Question 16

What are signal sequences recognized by?

Answer 16

Complementary receptors

Question 17

Proteins needed in the nucleus are imported from where?

Answer 17

The cytosol.

Proteins are synthesized in the cytosol.

Question 18

Molecules such as tRNA and mRNA that are synthesized in the nucleus are exported where?

Answer 18

The cytosol

Question 19

What is the function of nuclear pore complexes?

Answer 19

They transport molecules from the nucleus in pot directions.

The transport is facilitated by binding of particles to fibrils extending from the NPC.

Question 20

What type of transport is used in nuclear pore complexes?

Answer 20

Passive diffusion of small molecules and facilitated transport.

Question 21

What are nuclear localization signals (NLS)?

Answer 21

Sorting signals that direct molecules to the nucleus. They result in the selective import of proteins into the nucleus.

Question 22

What are nuclear localization signals composed of?

Answer 22

Short sequences rich in positively charged amino acids lysine and arginine.

Question 23

What is NLS recognized by?

Answer 23

Nuclear import receptors (NIRs).

Question 24

What are nuclear import receptors (NIRs)?

Answer 24

Soluble cytosolic proteins that bind to NLS on protein and to NPS proteins present on fibrils that extend into the cytoplasm.

Question 25

What is found on NPS proteins that serve as binding sites for import receptors?

Answer 25

Phenylalanine glycine (FG) repeats.

Question 26

How do receptors traverse NPC?

Answer 26

By binding, dissociating and re-binding to adjacent FG repeats.

Question 27

What happens once receptors reach their destination (nucleus)?

Answer 27

Cargo is released inside the nucleus and NIR returns to the cytoplasm.

Question 28

What is needed in order for molecules to go out of the nucleus?

Answer 28

Nuclear export signals and complementary nuclear export receptors.

Question 29

What drives nuclear transport in the appropriate direction?

Answer 29

Gradient of Ran conformational states.

Question 30

How do import receptor and cargo enter the nucleus?

Answer 30

By interacting with FG repeats on NPC proteins.

Question 31

What occurs as Ran-GTP binds to a complex of import receptor and cargo?

Answer 31

The binding causes the release of cargo.

Question 32

In the cytoplasm, what is Ran-GTP hydrolyzed by?

Answer 32

Ran-GAP

Question 33

What do NLS and NES shuttle back and forth between?

Answer 33

The nucleus and cytosol.

Question 34

What is steady state localization dependent on?

Answer 34

The relative rate of transport. If the rate of import is greater an export, it is considered nuclear and vice versa.

Question 35

What are the functions of gene regulatory proteins?

Answer 35

They keep transport stringently controlled. They are kept out of the nucleus until needed. Transport is controlled by NLS and NES being turned on and off. Mechanisms include phosphorylation, proteolysis, binding to inhibitory proteins.

Question 36

What is the protective barrier of a cell?

Answer 36

Plasma membrane