Quiz 03 questions

Question 1

COPI is involved in?

Answer 1

involved in retrograde transport in Golgi

Question 2

ALTERNATIVE QUESTION: Clathrin and COPI recruitment GTPAases

Answer 2

1. coat sheds soon after pinching off
2. ARF-GAP monomeric GTPASE forms vesicle- activated by membrane curvature (uncoating)

Question 3

COPII

Answer 3

1. GTPase Sar1 promotes assembly of vesicle coat

Question 4

ALTERNATIVE QUESTION: COPII recruitment

Answer 4

1. stays in ER until target membrane is reached
2. kinase at target membrane phosphorylates coat proteins to finish coating

Question 5

Clathrin

Answer 5

forms three-legged triskelion ***(pentagons and hexagons) for membrane-bending and fission

Question 6

Compartmentalization of cells in the perinuclear space is……

Answer 6

topologically equivalent to extracellular space

Question 7

Imagine a protein that has engineered to contain a nuclear localization signal, a nuclear export signal, and a canonical ER signal sequence. Where would you expect to find the protein after its synthesis?

Answer 7

ER

Question 8

ALTERNATIVE QUESTION: Imagine a protein contains a nuclear localization signal, nuclear export signal, nuclear import/export receptors. Where would you expect to find the protein after its synthesis

Answer 8

shuttling between cytosol and nucleus

Question 9

ALTERNATIVE QUESTION: After protein synthesis, what does a protein need to move to the ER?

Answer 9

nuclear localization signal, a nuclear export signal, and a canonical ER signal sequence

Question 10

ALTERNATIVE QUESTION: After protein synthesis, what does a protein need to shuttle between the cytosol and nucleus?

Answer 10

a nuclear localization signal, nuclear export signal, nuclear import/export receptors

Question 11

ALTERNATIVE QUESTION

receptor-mediated encoytosis of LDL particles mechanism

Answer 11

1. LDL receptors on plasma membrane recognized by AP2
2. Low pH in EARLY endosome dissociates LDL from receptor and recycled
3. digested in endolysosomal system to release free cholesterol

Question 12

RECEPTOR MEDIATED endocytosis of LDL particles

Answer 12

LDL receptors at the plasma membrane usually concentrated in clathrin-coated pits

Question 13

ALTERNATIVE QUESTION

LDL dissociates from its receptor at low pH in the early endosome (EE). The LDL receptor is packaged into vesicles at EE tubules. The LDL particle stays in the vacuolar portion of the EE that matures to late endosomes. What simple fact might contribute to the efficient separation of the fates of LDL and its receptor?

Answer 13

The LDL receptor is a membrane protein, whereas LDL is a soluble particle. The early endosome comprises tubular and vacuolar portions. When transport vesicles only bud off from the tubular region, LDL receptor is likely incorporated and LDL likely excluded, because the ratio of the membrane area to volume is large at the tubules and low at the vacuolar regions.

Question 14

Rab5 and Rab7 constitute a Rab cascade in the process of endosome maturation. One of the Rab5 effectors is a Rab7-GEF, while one of the Rab7 effectors is a Rab5-GAP. Which of these proteins would you expect to find in early endosomes?

Answer 14

Rab 5

Question 15

Rab 5 is found where?

Answer 15

early endosomes

Question 16

Rab 7 is found where?

Answer 16

late endosomes

Question 17

We talked about two general types of intracellular molecular switches, monomeric switches, monomeric GTPases and phosphorylated proteins. These switches can be turned in the on and off state. Monomeric GTPases are always off when….?

Answer 17

GDP is bound to them

Question 18

ALTERNATIVE QUESTION: Monomeric GTPases are always on when?

Answer 18

GTP is bound to them

Question 19

ALTERNATIVE QUESTION: Other molecular switches are…..

Answer 19

not specified: do not depend on phosphorylation, GTP/GDP

Question 20

What is a major consequence of activation of phospholipase C-B (PLCB) by the Gq trimeric GTPase?

Answer 20

Elevation of intracellular calcium = activation of PKC **PKC = protein kinase C

Question 21

The transport of most nuclear cargo through the nuclear pore complex is mediated by karyopherins and relies on simple diffusion. 1) Describe why cells need to employ a mechanism to impart directionality on this process 2) How it works 3) What monomeric GTPase is involved in this process.

Answer 21

Nuclear transport through NPCs increases order in the cell by coupling to energetically favorable reactions.** The cell fuels this “ordering” process by harnessing energy stored in concentration gradients of the GTP-bound form of **GTPase Ran.

The directionality of nuclear import and export is due to differential localization of Ran-GTP in the nucleus and Ran-GDP in the cytosol. Ran-GAP triggers GTP hydrolysis to produce Ran-GDP in the cytosol of the NPC. Since Ran-GDP in the cytosol does not bind to import/export receptors, unloading occurs ONLY on the nuclear side of the NPC.

Question 22

Ran

Answer 22

monomeric GTPase that provides directionality for transport through NPCs

Question 23

Ran-GAP role in nuclear transport

Answer 23

Nuclear transport: GTPase activating protein triggers GTP hydrolysis to convert Ran-GTP to Ran-GDP in the cytosolic side of the NPC

Question 24

Ran-GEF role in nuclear transport

Answer 24

Nuclear transport: Guanine nucleotide exchange factor promotes conversion of GDP to GTP

Question 25

Where are the following GTPases located? 1) Ran-GAP 2) Ran-GEF

Answer 25

1) Ran-GAP (cytosol) 2) Ran-GEF (nucleus anchored to chromatin)

Question 26

****Modified**** (more binding sites than original quiz)

Draw an activation curve for an allosteric protein with 1, 2, 8, and 16 binding sites for the effector protein.

Answer 26