Pumps and transporters Flashcards
T/F. GLUT4 transports glucose, is expressed in muscle and is regulated by insulin
All true
Most abundant transporter family
Secondary transporters
why are there relatively few genes encoding pumps
pumps initiate chemiosmotic circuits that drive many transporters and circuits
three main carrier mechanisms
uniport (facilitated diffusion, substrate moves alone), antiport (substrates exchange) and symport (cotransport, substrates move in same direction)
T/F. Kinetics of RBC glucose transport occurs with both enantiomers of glucose
False, D-glucose moves in a lot faster
carrier hypothesis
carrier protein changes orientation as it moves substrate in and out
Gradient of what macromolecule can drive H+ uptake
Sugar
GLUT1 function
glucose uptake in brain, absence causes seizures
GLUT2 function
glucose exit from hepatocytes, kidney - mutations cause Fanconi syndrome/glycogen storage disorder
SGLT1/2 function
active sugar absorption in gut/kidney
polytopic membrane proteins
go in and out of membrane many times
F-type ATPase:: mechanism of action and actions of subunits
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
V-type ATPase:: location and function
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
what are different pump energy sources (5)
light (bacteriorhodopsin), redox potential (NADH oxidase), decarboxylation, pyrophosphate, and ATP
What are the diffs between F1F0 and V1V0 ATPases
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
What other energy-requiring processes are ion gradients driving?
cell homeostasis, osmotic/cell volume regulation, chemical, signal transduction, and mechanical processes
P-type ATPase:: location and function
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
energy of ATP can reside in two components
concentration gradient and/or electrical gradient
ABC transporters:: location and functions
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
How does glucose transport in an enterocyte work?
Glucose co-transported with sodium, diffuses to blood, drives antiport of potassium and H+
What is the typical topology of a carrier protein?
12 transmembrane domains, positive inside, transmembrane positive charges are either ion paired or important for transport. Also, N and C terminal ends are homologous
T/F. Bacteria have ABC importers and exporters, eukaryotes have only exporters
True
What makes ABC transporters unconventional pumps?
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
