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Flashcards in MR S2 Deck (45):
0

What is passive transport reliant on?

Membrane permeability
Concentration gradient

1

Order these molecule types in order of most to least permeable to phospholipid membranes:
Ions
Hydrophobic molecules
Small uncharged polar molecules
Large uncharged polar molecules

Hydrophobic molecules
Small uncharged polar molecules
Large uncharged polar molecules
Ions

2

Describe active transport

Allows transport of ions against an unfavourable concentration gradient and/or electrical gradient
Energy directly or indirectly from ATP
Some cells spend 30-50% of their energy on active transport

3

What is the approximate free ion concentration of sodium intra and extracellularly?

Intra: ~12mM
Extra: ~145mM

4

How does increased concentration gradient affect rate of passive transport?

Rate of passive transport increases linearly with increasing concentration gradient

5

What is the approximate free ion concentration of calcium intra and extracellularly?

Intra: ~10^-7M
Extra: ~1.5mM

6

What is the approximate free ion concentration of chlorine intra and extracellularly?

Intra: ~4.2mM
Extra: ~123mM

7

What is the approximate free ion concentration of potassium intra and extracellularly?

Intra: ~4mM
Extra: ~155mM

8

What are the two types of transporter involved in co transport?

Symport
Antiport

9

What is a uniport?

A transport protein which moves one molecule per cycle

10

What is a co transporter?

A transport protein which simultaneously transports two molecules per cycle

11

What is PMCA?

A primary active transporter
Full name: plasma membrane calcium ATPase
Moves calcium ions across a membrane using ATP

12

Why do co transporters use secondary active transport?

They use the concentration gradients of one molecule to transport an extra molecule
Aka they don't directly use ATP
BUT still active transport because the concentration gradients that allow co transport are set up by membrane proteins which require ATP.

13

What is the Na+K+ATPase (aka Na+ pump)?

Moves 2 K+ ions into the cell and 3 Na+ ions out of the cell (usually against their concentration gradients) simultaneously
Requires ATP
A P-type ATPase
~25% of BMR used for this protein

14

What is ATP synthetase?

Active transport in reverse mode
Uses high proton concentration gradient to produce ATP
Seen in electron transport chain/oxidative phosphorylation

15

What type of active transport occurs in co transporters?

Secondary

16

Why is the Na+ K+ pump important?

Sets up Na and K gradients
Responsible for ~-5mV of the membrane potential
Necessary for electrical excitability
Drives many secondary active transport regulatory processes eg:
-ion homeostasis
-pH
-Cell volume
-Ca concentration
-resting potential
-nutrient uptake eg glucose uptake in small intestine

17

Name two calcium transporters

Ca2+ Mg2+ ATPase
Na+ Ca2+ Exchanger (NCX)

18

What is the difference between a symport and an antiport?

Symports transport two molecules in the same direction across a membrane
Antiports transport two molecules across a membrane in different directions

19

Describe the Na+ Ca2+ Exchanger (NCX)

Antiport
Moves one Ca out and three Na in per cycle
Low affinity, high capacity

Transport of Na ions down concentration gradient provides energy for transport of Ca against concentration gradient.

20

Describe the Ca2+ Mg2+ ATPase transporter

Moves one Ca or Mg out of the cell
Active transporter
Requires ATP
High affinity, low capacity

21

Describe the Na H exchanger (NHE)

Antiport
Exchanges one extracellular Na for one intra cellular H
Electroneutral (1:1 ion exchange)
Regulates pH
Regulates cell volume
Inhibited by amiloride
Activated by growth factors

22

Describe the Na glucose co transporter

Symport
Entry of Na provides enough energy for entrance of glucose into cell agains concentration gradient

Important in small intestine and kidney

23

What can increase the passive transport of water?

Increased osmotic gradient
Water channels aka aquaporins

24

Where can aquaporins be found?

The proximal kidney tubules

25

Why are hydrophilic molecules less likely to cross a membrane?

Has to travel through hydrophobic area
So would require high free energy (ΔG) change
So thermodynamically unlikely

26

What are some important roles of transport systems?

Maintenance of intracellular pH
Maintenance of ionic composition
Regulation of cell volume
Concentration of metabolic fuels and building blocks
Extrusion of waste products of metabolism and toxic substances
Generation of ionic gradients necessary for electrical excitability of nerve and muscle tissue

27

What are the models for facilitated transport?

Protein pores (aka channels)
Carrier molecules (ping-pong)
Flip flop (thermodynamically unlikely)

29

Why is control of calcium so important?

There's a ~20 000 fold difference between intra and extra cellular calcium so VERY tightly controlled
High intracellular calcium is highly toxic to cells
Cells signal by SMALL changes of intracellular calcium

30

What is SERCA?

Sarco(Endo)plasmic Reticulum Ca2+ ATPase
Transports calcium into and protons out of the endoplasmic/sacro plasmic reticulum
Uses ATP
High affinity, low capacity

31

What is the mitochondrial Ca uniport and when is it used?

Uses facilitated diffusion
Operates at high intracellular Ca concentrations to buffer potential damaging calcium

33

What are the types of gated pores?

Ligand gated channels - open or close in response to binding of ligand to receptor site
Voltage gated channels - open or close in response to change in normal membrane potential
Gap junctions - these close when intracellular calcium rises above 10μM or when cell becomes acid

34

Does NCX always pump ions in the same direction? What effect does this have?

No, in depolarisation NCX's normal function is reversed
This contributes to the Ca influx during the cardiac action potential
Can also contribute to Ca toxicity ischaemian

35

Name some membrane proteins involved in control of pH

NHE aka Na H exchanger
NBC aka sodium bicarbonate cotransporter aka Na dependent Cl/HCO3 exchanger
AE aka Anion transporter aka Cl/HCO3 exchanger

36

Name the bicarbonate transporters and their actions

AE acidified the cell
NBC alkalinises the cell

Both are involved with cell volume regulation

37

What is facilitated diffusion?

The membrane permeability of a substance can be increased by the incorporation of certain membrane proteins into the membrane
Relies on concentration/electrical gradient for substrate movement

38

Outline bicarbonate reabsorption in the proximal tubule

Na/K pump sets up Na gradient
NHE pumps H out of cell
H "picks up" bicarbonate and brings it back into the cell

39

Describe the theory of renal hypertensive therapy

The goal is to reduce mineral ion reabsorption from urine
Therefore less water returns via osmosis
Therefore blood volume and so blood pressure falls

40

Describe aquaporin

Allows water to readily cross the membrane
It's inclusion in membranes is stimulated by ADH

41

Describe loop diuretics

Block Na reuptake in thick descending limb of kidney

42

Describe amiloride

Prevents the reuptake of Na
Acts in the distal convoluted tubule on ENaC
Acts on the proximal tubule on NaH

43

What action does aldosterone have?

Up regulates transporters in the kidney to increase ion and water reabsorption in the kidney

44

Describe spironolactone

Gluticocorticoid antagonist
Used to treat high aldosterone levels

45

Describe the role of membrane transporters in cystic fibrosis

Na/K pump sets up gradient
CFTR protein non-functional
Cl builds up in cell
Water moves into cell
Mucus is thick and sticky

46

What is the role of transport proteins in diarrhoea?

CFTR protein overly active after phosphorylated by ATP
Cl transported into lumen of gut
Water follows
~diarrhoea~