Lecture 4 - Pores, Channels And Transporters

Question 1

What is active transport?

Answer 1

Transport of ions or molecules against the concentration gradient using energy directly or indirectly from hydrolysis of ATP

Question 2

What is primary active transport?

Answer 2

Active transport which directly uses the energy from the hydrolysis of ATP to transport molecules against their concentration gradient

Question 3

What is secondary active transport?

Answer 3

Type of Co-transporter

When an electrochemical gradient is set up by an ATPase is then used to transport another ion or solute against its gradient

Use a pre-existing electrochemical gradient to co-transport a molecule against its concentration gradient

Question 4

What are the 4 primary active transporters i need to know?

Answer 4

Na+/K+ pump (sodium pump)
Calcium ATPases (PMCA and SERCA)
K+/H+ ATPase (Proton pump)
F1/F0 ATPase (ATP synthase, doesn’t hydrolyse ATP)

Question 5

Where is the SERCA transporter protein located?

Answer 5

Sarcoplasmic reticulum of skeletal muscle cells

Question 6

What type of co-transport is occurring with a Na+/K+ ATPase or sodium pump?

Answer 6

Antiport

Question 7

Where a sodium pump is concerned, what are the relative concentrations of Na+ and K+ inside and outside of the cell?

Answer 7

K+ high inside cell low outside

Na+ high outside cell, low inside

Question 8

With the Na+/K+ ATPase (sodium pump), how many sodium ions and how many potassium ions are being transported?

Answer 8

3 Na+
2 K+

Question 9

Which direction is Na+ being actively transported and which direction is K+ being actively transported with the sodium pump?

Answer 9

2 K+ pumped into cell
3 Na+ pumped out of cell

Question 10

Why is a sodium pump an example of a primary active transporter?

Answer 10

Uses energy directly from the hydrolysis of ATP to actively transport both K+ and Na+ against their gradients

Question 11

Which amino acid on the sodium pump gets phosphorylated from the Pi from hydrolysed ATP?

Answer 11

Phosphorylates Aspartate
Makes phosphoenzyme intermediate

Question 12

How does the sodium pump work?

Answer 12

ATP hydrolysed (Aspartate phosphorylated) causes conformational change
3 Na+ taken into their high affinity sites
Conformational change opens the protein so Na+ can be released out of the cell
Conformational change allows 2 K+ to bind to pump
Conformational change opens pump to inside the cell phosphate released causing K+ site to have low affinity for K+ so released into cell

Question 13

What is the structure of the sodium pump?

Answer 13

2 subunits
Alpha and beta

Question 14

What is the function of the alpha subunit of the sodium pump?

Answer 14

Where all the work is done:
Where phosphate binds and where ions pumped

Has Ouabain receptor

Question 15

What is the function of the Beta subunit of the sodium pump?

Answer 15

A glycoprotein which puts sodium pump on plasma membrane of cell

Question 16

What is Ouabain?

Answer 16

Cardiac glycoside

Binds to sodium pump preventing it from functioning

Question 17

What is the function of the Na+/K+ ATPase (Na+ pump)

Answer 17

Forms Na+ and K+ gradients for electrical excitability

Drives secondary active transport (set up electrochemical gradient)

Question 18

What is the main contributor to maintaining membrane resting potential?

Answer 18

Leaky K+ channels

Question 19

Which ion is toxic to the heart?

Answer 19

K+

Question 20

What is the normally K+ serum levels in the blood?

Answer 20

4mM

Question 21

The concentrations of which ions are normally always greater outside the cell compared to inside?

Answer 21

Ca2+
Na+
Cl-

Question 22

Why is calcium toxic to cells?

Answer 22

Activates enzymes that shouldn’t be activated

Calcium phosphate crystallises in the cell killing the cell

Calcium influx in mitochondria causes apoptosis

Question 23

Why is it useful the concentration of calcium being so much lower inside the cell compared to the outside?

Answer 23

Can utilise calcium for certain process

Question 24

What is another name for a plasma membrane Ca2+ ATPase?

Answer 24

PMCA

Question 25

What is the role of PMCA? (Plasm membrane Ca2+ ATPase)?

Answer 25

Exclude Ca2+ ions from the cell

Question 26

What type of transport does the PMCA primary active transporter use?

Answer 26

Uniport

Question 27

What other transporter protein expels calcium from the cell?

Answer 27

NCX (Na+/Ca2+)

Question 28

What is the difference between PMCA and NCX?

Answer 28

NCX = Secondary active transporter + antiporter PMCA = Primary active transporter + Uniporter

Question 29

How does the affinity and capacity of PMCA compare to NCX?

Answer 29

PMCA = High affinity BUT Low Capacity (Ca2+ binds well but cant move a lot) NCX = Low affinity BUT High capacity (Ca2+ doesn’t bind well but can move lots at once)

Question 30

What is the name of the calcium transporter found on the membrane of the sarcoplasmic reticulum?

Answer 30

SERCA (SarcoEndoplasmic reticulum Ca2+ ATPase)

Question 31

What type of Ca2+ transporter exists in the mitochondria?

Answer 31

Ca2+ uniporter

Question 32

What is the pathology of Duchenne muscular dystrophy?

Answer 32

Too much Ca2+ enters into mitochondria Water drawn into mitochondria Mitochondria burst Replaced with adipocytes

Question 33

How can Ca2+ entering mitochondria cause cell death?

Answer 33

Ca2+ can activate caspases causing apoptosis

Question 34

What is unique about the F1/F0 ATPase (ATP synthase)?

Answer 34

Synthesises ATP rather than hydrolysing it

Question 35

Briefly describe how the F1/F0 ATPase (ATP synthase) transporter works:

Answer 35

Proton gradient from inter membrane space to matrix exists H+ binds to F0 which rotates allowing H+ to pass back into the matrix F1 rotates rotates and Phosphorylates ADP and Pi to ATP

Question 36

How many H+ must pass through the F1/F0 ATPase complex to produce 1 ATP molecule?

Answer 36

3 H+ = 1 ATP

Question 37

What type of transporter is Sodium Glucose Cotransporter 1/2 (SGLT-1 or SGLT-2)?

Answer 37

Secondary active transporter Symporter

Question 38

How many Na+ does SGLT-1 move in for every glucose?

Answer 38

2 Na+

Question 39

How many Na+ does SGLT-2 move in for every glucose?

Answer 39

1 Na+

Question 40

What is the importance of Organic Anion Transporter (OAT) and Organic Cation Transporter (OCT)?

Answer 40

How many drugs enter into cells

Question 41

What is the role of the Na+/Ca2+ exchanger (NCX)?

Answer 41

Expels intracellular Ca2+ from cell during recovery (while cell is repolarising)

Question 42

What type of transporter is NCX?

Answer 42

Antiporter Secondary active transporter

Question 43

How many molecules of Na+ are moved into the cell and how many Ca2+ ions are moved out of the cell per cycle by NCX?

Answer 43

3 Na+ in 1 Ca2+ out

Question 44

How does charge within the cell usually change as NCX is active?

Answer 44

Becomes more positive by +1 each exchange (3+ in cell , 2+ out of cell net gain of +1)

Question 45

What is reperfusion?

Answer 45

Restoration of blood flow to a region normally following an arterial occlusion allowing for wastes to begin to be removed from the tissues

Question 46

What happens to NCX when the membrane is polarised?

Answer 46

Ca2+ pumped into cell Na+ pumped out Function of NCX flips

Question 47

How does NCX function in ischaemia?

Answer 47

Blood supply cut of leads to lack of O2 so depletion of ATP Sodium pump cant act Na+ accumulates in cell and cell becomes very positive so is depolarises Depolarised membrane causes NCX function to flip so 3 Na+ expelled from cell as 1 Ca2+ pumped into cell Ca2+ builds up in cell, cell dies

Question 48

What are the 2 primary active transport methods of controlling resting Ca2+ conc in the cell?

Answer 48

PMCA SERCA

Question 49

What is the secondary active transport method of controlling resting calcium concentration?

Answer 49

NCX

Question 50

What is the method of controlling resting calcium concentration via facilitated diffusion?

Answer 50

Mitochondrial Ca2+ uniports Buffer potentially damaging calcium concentrations

Question 51

What does the Na+/H+ exchanger transport? (NHE)

Answer 51

1 Na+ into cell 1 H+ out of cell No net change in charge

Question 52

What type of transport is used by NHE (Sodium proton exchanger)?

Answer 52

Secondary active transport Antiport

Question 53

What is the role of NHE (Na/H+ exchanger)?

Answer 53

Regulates pH Regulates cell volume

Question 54

How does NHE regulate cell volume?

Answer 54

As sodium brought into cell, water is brought with it

Question 55

What is Amiloride?

Answer 55

Drug that targets the NHE

Question 56

What is the function of amiloride?

Answer 56

Inhibits NHE Prevents Na+ and water being drawn back into kidney cells Is a diuretic (does take potassium with it)

Question 57

What is the importance of the sodium pump (Na+/K+ ATPase) carrier protein in regulating cellular pH?

Answer 57

Establishes Na+ gradient (electrochemical gradient) so secondary active transport can take place at other transporters to regulate pH

Question 58

Which transporters lead to acid extrusion from a cell?

Answer 58

NHE Sodium Bicarbonate Chloride transporter

Question 59

Which transporters cause alkali influx into cells?

Answer 59

Sodium Bicarbonate Chloride transporter (NBC) Sodium Bicarbonate transporter

Question 60

Which transporter extrudes alkali from then cell no which cells are they commonly in?

Answer 60

Anion exchanger (AE) Like band 3 in RBCs

Question 61

Where in the kidney is blood glucose controlled?

Answer 61

Nephron

Question 62

What would happen if selective reabsorption did not happen in the nephron?

Answer 62

Na+, HCO3-, H2O and glucose would all be lost from the body in urine RAPID DEHYDRATION AND COMA

Question 63

What type of kinetics do carrier proteins experience and why?

Answer 63

Michaelis Menton Kinetics All sites get saturated and rate conformational changes occurring can’t change

Question 64

In the gut (enterocyte) which glucose transporter is present on the apical surface?

Answer 64

SGLT-1 (Sodium glucose co-transporter 1)

Question 65

In the gut (enterocyte) which glucose transporter is found on the base lateral surface?

Answer 65

GLUT-2

Question 66

Where SGLT-1 is present, what other transporter will always be found on the basolateral surface?

Answer 66

GLUT-2

Question 67

What type of active transport does the K+/H+ ATPase transporter do? (Proton pump)

Answer 67

Primary active transport Directly uses energy from hydrolysis of ATP

Question 68

What is the role of the K+/H+ ATPase in the enterocyte?

Answer 68

Sets up proton gradient So proton and sucrose can by symporter from gut lumen into enterocyte across Sucrose-proton cotransporter

Question 69

What type of active transport is used by the sucrose-H+ Cotransport at the gut?

Answer 69

Secondary active transport

Question 70

How many sections are there of the PCT of the nephron?

Answer 70

3

Question 71

Which SGLT transporter is used in segment 1 of the PCT to transport glucose back in to the epithelial cell?

Answer 71

SGLT2

Question 72

What SGLT transporter is used in segment 2 and 3 in the PCT to reabsorb glucose into the epithelial cells?

Answer 72

SGLT1

Question 73

Which glucose exporter is used to put glucose back in the blood in segment 1 in the PCT?

Answer 73

GLUT 2

Question 74

Which glucose exporter is used to put glucose back in the blood in segment 2 and 3 of the PCT?

Answer 74

GLUT1

Question 75

Action of SGLT2 and SGLT1 inhibitors in Type 2 diabetes Mellitus?

Answer 75

SGLT2 inhibitors inhibit glucoses uptake in kidney SGLT1 inhibitors inhibit intestinal absorption

Question 76

What is phlorizin?

Answer 76

SGLT2 inhibitor

Question 77

What is the main glucose transporter in the liver?

Answer 77

GLUT 2

Question 78

What is the main glucose transporter in muscles and adipose?

Answer 78

GLUT 4

Question 79

What hormone regulates expression of GLUT 4?

Answer 79

Insulin promotes

Question 80

Where is GLUT1 found?

Answer 80

CNS (Astrocytes)

Question 81

What are MCT proteins?

Answer 81

Symporters of H+ and lactate ions from Astrocyte to neurone

Question 82

What pathways is glucose transported in the CNS?

Answer 82

Glucose into Astrocyte via GLUT1 GLucose converted to lactate Lactate transported to neurone via MCT Glucose via GLUT1 via endothelial cells into interstitial space GLUT3 into neurone

Question 83

What type of transport happens across GLUT transporters?

Answer 83

Facilitated diffusion

Question 84

What drives the transport of glucose across SGLT transporters?

Answer 84

Na+/K+ ATPases

Question 85

How does glucose uptake into skeletal muscles and adipose tissue increase with insulin?

Answer 85

Insulin binds to Tyrosine kinase receptor Receptor phosphylates itself Activates secondary messenger cascade Vesicles containing GLUT 4 proteins fuse to plasma membrane of cells

Question 86

Which glucose transporter is present at the blood brain barrier?

Answer 86

GLUT-1

Question 87

Which glucose transporter is present in neurones?

Answer 87

GLUT-3

Question 88

Why it essential that GLUT-1 and GLUT-3 have very low Km for glucose?

Answer 88

So brain and neurones receive as much glucose as possible to prevent death

Question 89

Describe how glucose is transported from the gut lumen into the blood:

Answer 89

Na+/K+ ATPase pumps 3 Na+ out of cell into blood and 2K+ from blood into cell (basolateral surface) SGLT1 Moves 2 Na+ with 1 glucose from apical surface into cell GLUT2 moves glucose into the blood from the cell

Question 90

Which has a lower Km, SGLT1 or SGLT2?

Answer 90

SGLT 1 since it works at lower concentrations (think of the kidney PCT)

Question 91

Which glucose transporter reabsorb most of the glucose back into the PCT?

Answer 91

SGLT2