Pumps and transporters

Question 1

T/F. GLUT4 transports glucose, is expressed in muscle and is regulated by insulin

Answer 1

All true

Question 2

Most abundant transporter family

Answer 2

Secondary transporters

Question 3

why are there relatively few genes encoding pumps

Answer 3

pumps initiate chemiosmotic circuits that drive many transporters and circuits

Question 4

three main carrier mechanisms

Answer 4

uniport (facilitated diffusion, substrate moves alone), antiport (substrates exchange) and symport (cotransport, substrates move in same direction)

Question 5

T/F. Kinetics of RBC glucose transport occurs with both enantiomers of glucose

Answer 5

False, D-glucose moves in a lot faster

Question 6

carrier hypothesis

Answer 6

carrier protein changes orientation as it moves substrate in and out

Question 7

Gradient of what macromolecule can drive H+ uptake

Answer 7

Sugar

Question 8

GLUT1 function

Answer 8

glucose uptake in brain, absence causes seizures

Question 9

GLUT2 function

Answer 9

glucose exit from hepatocytes, kidney - mutations cause Fanconi syndrome/glycogen storage disorder

Question 10

SGLT1/2 function

Answer 10

active sugar absorption in gut/kidney

Question 11

polytopic membrane proteins

Answer 11

go in and out of membrane many times

Question 12

F-type ATPase:: mechanism of action and actions of subunits

Answer 12

ATP synthesis using H+ gradient in mitochondria/chloroplasts
F1Fo ATP synthase
F1 sector: water soluble & catalyzes ATP-hydrolysis
Fo sector: membrane-embedded and conducts H+
Redox driven, create transmembrane H+ gradient

Question 13

V-type ATPase:: location and function

Answer 13

establishes H+ gradients in endomembrane (for uptake of solutes via coupled transport) compartments (i.e. vacuoles, lysosomes) and specialized cell plasma membranes
2nd function - acidification, stimulates receptor mediated endocytosis

Question 14

what are different pump energy sources (5)

Answer 14

light (bacteriorhodopsin), redox potential (NADH oxidase), decarboxylation, pyrophosphate, and ATP

Question 15

What are the diffs between F1F0 and V1V0 ATPases

Answer 15

F1F0 acts both as an ATPase and ATP synthase and can function as separate subunits
V1V0 is only an ATPase and can only act when properly assembled
V1Vo is more structurally complicated

Question 16

What other energy-requiring processes are ion gradients driving?

Answer 16

cell homeostasis, osmotic/cell volume regulation, chemical, signal transduction, and mechanical processes

Question 17

P-type ATPase:: location and function

Answer 17

Function in ion exchange at plasma membrane (have a phosphorylated intermediate stage-why called P-type)
**Responsible for ion gradients that allow action potential & other gated channel-mediated events to occur
Examples: Na/K- ATPase, H/K-ATPase and Ca/H-ATPase
All P-type pumps are structurally similar
There are inherited disorders relating to P-ATPases and clinically they are relevant as cardiac glycosides and anti-ulcer drugs target these pumps

Question 18

energy of ATP can reside in two components

Answer 18

concentration gradient and/or electrical gradient

Question 19

ABC transporters:: location and functions

Answer 19

Everything else that uses ATP and transports stuff, found in all membranes
ABC transporters resemble each other
Examples: CFTR, MDR2, MDR1, SUR, ALDP and PMP70
Mutations in CFTR cause cystic fibrosis
Overexpression of MDR1 in cancer confers chemotherapeutic drug resistance

Question 20

How does glucose transport in an enterocyte work?

Answer 20

Glucose co-transported with sodium, diffuses to blood, drives antiport of potassium and H+

Question 21

What is the typical topology of a carrier protein?

Answer 21

12 transmembrane domains, positive inside, transmembrane positive charges are either ion paired or important for transport. Also, N and C terminal ends are homologous

Question 22

T/F. Bacteria have ABC importers and exporters, eukaryotes have only exporters

Answer 22

True

Question 23

What makes ABC transporters unconventional pumps?

Answer 23

In CFTR types – not only a Cl- channel, but ATP hydrolysis can be used to gate channels, not stoichiometrically coupled to ion mvmt.
In MDR2 types – transport happens within leaflets of bilayer
In MDR1 types – super nonselective