Membrane Permeability

Question 1

Define membrane permeability

Answer 1

The ability of a membrane to allow molecules to pass through

Question 2

What is passive diffusion?

Answer 2

Molecules move from an area of high concentration to an area of low concentration without using energy

Question 3

What is facilitated transport?

Answer 3

The usage of channels to transport molecules or ions across a membrane without the use of energy

Question 4

What is active transport?

Answer 4

The movement of molecules or ions from an area of low concentration to an area of high concentration with the use of energy

Question 5

What is a semi-permeable membrane?

Answer 5

A layer through which only certain substances are allowed to pass

Question 6

Which class of molecules are lipid bilayer most permeable to?

Answer 6

Hydrophobic molecules (eg oxygen, carbon dioxide, nitrogen and benzene)

Small uncharged polar molecules (eg water, urea, glycerol)

Question 7

What do permeability coefficients tell us?

Answer 7

Higher permeability coefficient - higher permeability

Cm/s

Question 8

What is passive transport dependent on?

Answer 8

Permeability and concentration gradient

Rate of transport increases linearly with increasing concentration gradient

Question 9

What are transport processes important for?

Answer 9

• Maintenance of ionic composition
• Maintenance of intracellular pH (movement of H+)
• Regulation of cell volume
• Concentration of metabolic fuels and building blocks
• The expulsion of metabolic waste products and toxic substances (eg urea)
• The generation of ion gradients necessary for the electrical excitability of nerve and muscle

Question 10

What is the accepted model of membrane transport proteins?

Answer 10

‘Ping-pong transport’

Molecule binds, protein internalises, conformational change

Question 11

If /\G is positive/negative what does this mean?

Answer 11

Positive = active transport
Negative = passive transport

Question 12

Where is the energy that is required in active transport taken from?

Answer 12

Hydrolysis of ATP

Question 13

What is the approximate value of intracellular ca2+?

Answer 13

10^-7 M

Question 14

What is the approximate value of extracellular ca2+?

Answer 14

1.0 - 1.5 mM

Question 15

What is the approximate value of intracellular Cl-?

Answer 15

4.2mM

Question 16

What is the approximate value of extracellular Cl-?

Answer 16

123 mM

Question 17

What is the approximate value of intracellular K+?

Answer 17

155mM

Question 18

What is the approximate value of extracellular K+?

Answer 18

4mM

Question 19

What is the approximate value of intracellular Na+?

Answer 19

12mM

Question 20

What is the approximate value of extracellular Na+?

Answer 20

~145mM

Question 21

What is Ca2+ ATPase an example of?

Answer 21

Primary active transporter (uses ATP)

Question 22

What is uni-transport?

Answer 22

Only one molecule transported at a time

Question 23

What is symport?

Answer 23

Two molecules are transported at the same time in the same direction

Question 24

What is anti port?

Answer 24

Two molecules are transported at the same time in opposite directions

Question 25

How many Na+ ions are pumped out of the cell compared to K+ ions?

Answer 25

3 Na+ out | 2 K+ in

Question 26

What do the alpha and beta subunits of the sodium pump do?

Answer 26

Alpha unit - K+, Na+, ATP binding sites | Beta unit - glycoproteins directs pump to cell surface

Question 27

What is mainly responsible for the resting membrane potential being -70mV?

Answer 27

K+ diffusion through channels

Question 28

What is the primary active transporter associated with Ca2+?

Answer 28

Ca2+ Mg2+ ATPase (uses ATP) Uniport

Question 29

What is the secondary transporter associated with Ca2+?

Answer 29

Na2+ Ca2+ exchanger (NCX) No ATP used Antiport

Question 30

Explain the Na+ Ca2+ exchange

Answer 30

Inwards flow of Na+ ions down the Na+ concentration gradient drives the outward flow of Ca2+ up its concentration gradient (antiport)

Question 31

Explain the Na+ H+ exchange

Answer 31

Inward flow of Na+ down its concentration gradient leads to cell alkalinisation by removing H+ (antiport)

Question 32

Explain Na+ glucose co transport (small intestine and kidney)

Answer 32

Entry of 2 Na+ ions provides the energy for the entry of 1 glucose molecule against its concentration gradient (symport)

Question 33

What percentage of basal metabolic rate is used to keep the sodium pump working?

Answer 33

25%

Question 34

Why is the sodium pump called a P-type ATPase

Answer 34

ATP phosphorylates aspartate, producing a phosphoenzyme intermediate

Question 35

Which subunit of the sodium pump directs pump to cell surface?

Answer 35

Beta subunit

Question 36

What creates the high intracellular concentration of potassium?

Answer 36

Sodium pump

Question 37

What is NCX driven by?

Answer 37

Na+ concentration outside the cell, not ATP

Question 38

Describe the Na+-glucose co transport system

Answer 38

Entry of 2Na+ provides the energy for the entry of 1 glucose molecule against its concentration gradient (symport)

Question 39

What does Fluoxetine inhibit?

Answer 39

Serotonin Reuptake Transporter (SERT)

Question 40

Which types of molecules can pass through the lipid bilayer?

Answer 40

Hydrophobic molecules eg O2, CO2, N2, Benzene | Small, uncharged polar molecules eg H20, urea, glycerol

Question 41

Which types of molecules cannot pass through the lipid bilayer?

Answer 41

Large uncharged polar molecules eg glucose and sucrose Ions eg Na+, K+, H+, Ca2+, Cl-

Question 42

How much more is the extracellular calcium ion concentration compared to intracellular?

Answer 42

10,000 times more

Question 43

What is an example of active transport in reverse mode?

Answer 43

ATP synthase

Question 44

What is uniport?

Answer 44

Involves the movement of one type of molecule or ion across the membrane

Question 45

What is an example of uniport?

Answer 45

GLUT1 glucose carrier

Question 46

What is symport?

Answer 46

Involves the movement of two or more different molecules or ions across a phospholipid membrane in the SAME direction

Question 47

What is an example of symport?

Answer 47

Na+/glucose cotransporter - 2Na+ and 1 glucose

Question 48

What is antiport?

Answer 48

Involves the movement of of two or more different molecules or ions across a phospholipid membrane in OPPOSITE directions

Question 49

What is an example of antiport?

Answer 49

NCX - 1Ca2+ for 3Na+

Question 50

Which type of transport is shown by the Na+-H+-Exchanger?

Answer 50

Antiport