Block 2 Lecture 21

Question 1

what is active transport

Answer 1

net movement of substrate against its electrochemical gradient. to do this energy has to come from a source other than the substrates own electrochemical gradient

Question 2

what are the two sources of energy for active transport

Answer 2

1. metabolic (chemical) energy

2. gradient energy

Question 3

what is metabolic (chemical) energy

Answer 3

energy derived from direct hydrolysis of ATP by the transport used to support primary active transport

Question 4

what is gradient energy

Answer 4

energy obtained through dissipation of energy in the electrochemical gradient of a different substrate. used to support secondary active transport

Question 5

what do ABC transporters do

Answer 5

primary active transporters, hydrolyze ATP to provide the energy for making substrates against their gradients

Question 6

what do ABC transporters do in mammals

Answer 6

pump potentially toxic compounds out of cells

Question 7

what do MDR transporters do

Answer 7

effective at clearing cells of toxic compounds they are very big proteins

Question 8

what do ion pumps do

Answer 8

• use ATP to move Na, K, Ca and/or H ions against their electrochemical gradients
• they are saturable and selective
• their activity involved hydrolysis of ATP they are all ATPases
• they are all P-type ATPases reflecting the fact that during the overall reaction cycle the transport protein itself is transiently phosphorylated, then dephosphorylated

Question 9

what are the p-type ATPases

Answer 9

• the Na, K ATPase
• the plasma membrane Ca-ATPase (PMCA)
• the sarco/endoplasmic reticulum Ca- ATPase (SERCA)
• the H,K ATPase

Question 10

what does the plasma membrane Ca-ATPase do

Answer 10

• pumps Ca2+ out of the cell

- works to keep the cytoplasmic Ca2+ concentration in the vicinity of 50-100 nM

Question 11

what happens when you inhibit Ca-ATPase

Answer 11

cytoplasmic Ca2+ will rise

Question 12

what does the sarco/endoplasmic reticulum Ca-ATPase (SERCA) do

Answer 12

• pumps Ca2+ into the smooth ER

- Ca2+ stored in the ER can be pumped into cytoplasm then brought back into the ER by SERCA using ATP

Question 13

what happens with SERCA when Ca2+ is increased

Answer 13

it activates a 2nd messenger cascade that influences phosphorylation which inhibits SERCA. when activated the second messenger system phosphorylates phospholamban and it relieves its inhibition of SERCA. net result is an increase in the rate of removal of Ca2+ from the cytoplasm back into the ER

Question 14

what happens if SERCA is inhibited

Answer 14

cytoplasmic Ca2+ increases

Question 15

what does the H, K-ATPase do

Answer 15

-pumps H+ out of some cells and K+ into the cell

Question 16

where is the H, K-ATPase located

Answer 16

PMCA and SERCA are virtually invert cell but the H,K-ATPase is mainly in parietal cells in the stomach but is now found in kidney where it plays a role in H+ and K+ balance. in the stomach they pump H+ into lumen of the stomach

Question 17

what does the Na,K-ATPase do

Answer 17

• pumps Na+ out and K+ in

- for both Na+ and K+ they are non equilibrium conditions so active transport must be involved

Question 18

how are charges fixed with the Na,K-ATPase

Answer 18

cells contain concentrations of proteins and nucleic acids that display a net negative charge. the negative charges of these fixed anions are countered by mobile cationic charges from Na+ and K+

Question 19

what is an inhibitor of Na pump activity

Answer 19

ouabain

Question 20

what does the outwardly directed K+ gradient do

Answer 20

results in an inside negative membrane potential which influences the transmembrane transport of all inorganic and organic ions

Question 21

what does the inwardly directed Na+ gradient do

Answer 21

plays a role in the generation of electrical action potentia in nerve cells, cardiac, and skeletal muscle

Question 22

how does the Na, K pump affect cell volume

Answer 22

if cell is left unchecked the osmotic imbalance will cause the cell to swell and lyse, to counteract this cells extrude cations

Question 23

what happens if the Na,K- ATPase is inhibited

Answer 23

cells swell

Question 24

what is the only V-type ATPase

Answer 24

V-type H-ATPase

Question 25

what does V-type H-ATPase do

Answer 25

pumps H+ into intracellular vesicles, acidifying the vesicle lumen (lysosomes and synaptic vesicles)

Question 26

what does the V-type H-ATPase do in lysosomes

Answer 26

activates enzymes found in vesicles

Question 27

what does the V-type H-ATPase do in synaptic vesicles

Answer 27

it works to create an outwardly directed H+ electrochemical gradient that is used to drive secondary active transport

Question 28

what is similar to V-type H-ATPase

Answer 28

F0F1 ATP synthase in the mitochondrial membrane, it basically runs backwards. it harnesses energy from ATP hydrolysis to pump H+

Question 29

what happens if V-type H-ATPase is inhibited

Answer 29

there will be a rapid collapse of the pH gradient between vesicles and cytoplasm because it doesn’t take long for the H+ in the vesicles to leak out into the cytoplasm because the volume of the vesicles are so low

Question 30

why does the V-type H-ATPase not have very large impact on cytoplasmic pH

Answer 30

because not that many protons are involved, the few extra H+ ions that enter the cytoplasm are transported out by plasma membrane transporters that regulate cytoplasmic pH

Question 31

what is the Na,K- ATPase called as a functional unit

Answer 31

a heterodimer

Question 32

what are the 3 parts to the Na,K- ATPase

Answer 32

alpha unit, beta unit, gamma unit

Question 33

what does the alpha unit in Na, K ATPase do

Answer 33

it is catalytic, it does the transport

Question 34

what does the beta unit in Na, K- ATPase do

Answer 34

plays a critical role in targeting the transporter to the right place in the cell

Question 35

what does the gamma subunit in Na,K- ATPase do

Answer 35

plays a regulatory role in some cells and sometimes refereed to as phospholemman

Question 36

what does phospholemman do

Answer 36

interacts with the alpha subunit and influences the apparent affinity of the transporter for Na+ regulating the rate of Na+ efflux

Question 37

what are the 3 physiological substrates for the Na-K-ATPase

Answer 37

intracellular Na+
extracellular K+
intracellular ATP

Question 38

since the Na, K-ATPase is a carrier mediated transport process what does that mean

Answer 38

increases in any 3 substrates can produce maximal rate, with the true maximal rate achieved only in the presence of saturating conditions of all 3 things

Question 39

what is the extracellular and intracellular concentrations of Na+

Answer 39

extracellular- 145mM

intracellular- 15mM

Question 40

what is the extracellular and intracellular concentrations of K+

Answer 40

extracellular- 4.5mM

intracellular- 120mM

Question 41

what is the extracellular and intracellular concentrations of Cl-

Answer 41

extracellular- 115mM

intracellular- 20mM

Question 42

what is the extracellular and intracellular concentrations of HCO3-

Answer 42

extracellular- 25mM

intracellular- 15mM

Question 43

what is the extracellular and intracellular concentrations of Ca2+

Answer 43

extracellular- 1mM

intracellular- 10^-4mM

Question 44

what is the extracellular and intracellular concentrations of H+

Answer 44

extracellular- 40 nM (pH 7.4)

intracellular- 60 nM (pH 7.2)