Membrane Transport

Question 1

Factors that control gating

Answer 1

Membrane voltage
Extracellular agonists/ antagonists
Intracellular messengers
Mechanical stretch of plasma membrane

Question 2

Ionotropic receptors

Answer 2

Activation of receptor causes pore to open that ions can pass through
(Tend to be for fast acting reactions)

Question 3

E.g.s of ionotropic receptors

Answer 3

Ligand gated sodium channels

Voltage gated sodium and calcium channels

Question 4

Metabotropic receptors

Answer 4

G protein coupled: Activation of receptor initiates intracellular signalling mechanisms (ions do not pass through receptor protein)
(Tend to be for more prolonged reactions)

Question 5

E.g.s metabotropic receptors

Answer 5

Metabotropic glutamate receptors (mGluRS)

Adrenergic receptors of autonomic nervous system

Question 6

Describe the membrane

Answer 6

Hydrophobic core
Barrier to almost all biologically important solutes
Intra/extracellular fluids mostly water
Gases and ethanol can diffuse across lipid bilayers
Movement of water and solutes restricted

Question 7

How does water move across the membrane

Answer 7

Aquaporins = water channels
Are widely distributed across the body
Different isoforms found in different cell types

Question 8

How is the amount of water influx/effluent regulated in cells?

Answer 8

Altering the number of aquaporins in the membrane

Changing membrane permeability e.g. by PH

Question 9

Uniporters

Answer 9

Transport a single molecule across a membrane

Question 10

Symporters

Answer 10

Couple the movement of 2+ molecules/ions across a membrane

The molecules are transported in the same direction

Question 11

E.g. of symporter

Answer 11

NKCC2
Found in the kidneys
Transports1Na+, 1K+, and 2Cl-
Important for diluting and concentrating urine

Question 12

What are the 3 major functional groups of solute carriers

Answer 12

Uniporters
Symporters
Antiporters

Question 13

Antiporters

Answer 13

Couple movement of 2+ molecules/ions across membrane in opposite directions
(Sometimes called exchangers or counter transporters)

Question 14

E.g.s antiporters

Answer 14

NHE-1
Na+ and H+ antiporters
Found in all cells
Important in regulating intracellular PH

Question 15

ATP dependent ion transporters

Answer 15

Found in all cells
3 subunits (a,b and y)
A subunit has binding sites for Na+, K+, ATP and Ouabain (inhibitory)

E.g. Na+, K+ATPase (also called Na+K+ pump)

Question 16

H+ATPase

Answer 16

Vacuolar H+ATPase found in membranes of many intracellular organelles
Plasma membrane H+ATPase important in urinary acidification

Question 17

Primary active transport

Answer 17

Transport is directly coupled to ATP hydrolysis

Question 18

Secondary active transport

Answer 18

Energy in the electrochemical gradient of one molecule is used to move another molecule(s) against its electrochemical gradient

Question 19

What does the Nernst equation calculate?

Answer 19

The equilibrium potential

Question 20

What does GHK calculate

Answer 20

How permeable a membrane is to certain ions

Question 21

Ion channels

Answer 21

Are selective

Can open and close And this can be recorded

Question 22

Gating

Answer 22

Fluctuation between open and closed states of ion channels

Question 23

GS proteins

Answer 23

Stimulatory G coupled receptors

Question 24

GI proteins

Answer 24

Inhibitory G coupled receptors

Question 25

Name some ATP depended processes

Answer 25

H+ATPase
Na+K+pump
ABC transporters

Question 26

ABC transporters e.g.

Answer 26

Cystic fibrosis transmembrane regulator

Question 27

Is extracellular fluid is hypotonic

Answer 27

Positive water balance

Cells undergo regulatory volume decrease to try and undo

Question 28

Is extracellular fluid is hypertonic

Answer 28

Negative water balance
Cells shrink then undergo regulatory volume increase to undo

Can lead to abnormal brain function
Cause: dehydration