Lecture 5- Membranes as permeability barriers

Question 1

Small hydrophobic molecules

Answer 1

will pass the bilayer e.g. Benzene, oxygen, carbon dioxide and nitrogen

Question 2

Small uncharged polar molecules

Answer 2

will pass the bilayer e.g. water, urea and glycerol

Question 3

Large uncharged polar molecules

Answer 3

will not pass bilayer without helps e.g. glucose and sucrose

Question 4

Ions

Answer 4

will not pass without help e.g. H+. K+, Na+, Cl

Question 5

transport processes (6)

Answer 5

• Maintain ionic composition
• Maintenance of intracellular pH
• Regulation of cell volume
• Concentration of metabolic fuels and building blocks
• Extrusion of waste products out of the cell
• Generate ion gradients necessary for the electrical excitability of nerves and muscles

Question 6

passive transport

Answer 6

Dependent on permeability and conc gradient
• Rate of passive transport increases linearly with increasing concentration gradient
• Always passive going down concentration gradient
• Exergonic (-ve)

Question 7

different membranes

Answer 7

have different permeability

• diff ion channels
• excitability of membrane

Question 8

membran proteins will not

Answer 8

flip flop

Question 9

ping pong transport

Answer 9

• Conformational change

- Maximum rate of transport exist

Question 10

facilitated fusion via…

Answer 10

Ion channels

• ligand gated
• voltage gated

Question 11

facilitated diffusion has a much higher

Answer 11

potential transport rate than simple diffusion

Question 12

active transport

Answer 12

• Where substances are pumped across the membrane against their conc gradient

Question 13

AT is an …. process

Answer 13

endergonic- more energy put into the reaction the comes out

Question 14

how much ATP used on AT

Answer 14

30-50%

Question 15

passive transport

Answer 15

simple diffusion and facilitated diffusion (transporter and channel)

Question 16

gradient for sodium

Answer 16

much more [sodium] outside the cell than inside

Question 17

gradient for potassium

Answer 17

much more [potassium] inside the cell than outsides

Question 18

gradient for calcium

Answer 18

[calcium] is high outside and low in inside

Question 19

gradient of chloride

Answer 19

[chloride] is high on the outside and low in inside

Question 20

primary active transporter

Answer 20

involves the movement of a solute against its electrochemical gradient facilitated by coupling to a process that provides the required free energy, e.g., Na+−K+ pump driven by ATP hydrolysis

Question 21

secondary active transport

Answer 21

involves the use of an electrochemical gradient, created by a primary active transporter e.g. Na+/K+ ATPase

Question 22

example primary active transporters

Answer 22

• Na+/K+ ATPase

- Plasma membrane calcium ATPase (PMCA) (pumps calcium out of the cell)

Question 23

example of active transport int he reverse mode

Answer 23

ATP synthase

- flow of protons powers creating of ATOP from ADP and Pi

Question 24

co transport exampels

Answer 24

uniport
symport
antiport

Question 25

uniport

Answer 25

transports a single molecule in one direction (not a co-transport)

Question 26

symport

Answer 26

more than one molecule in one direction

Question 27

antiport

Answer 27

more than one molecule transported in opposite directions e.g. Na/k+ ATPase (Na pump)
o Swaps 3 sodium (out) for 2 potassium (in)

Question 28

the sodium pump (Na/K+ ATPase) is an

Answer 28

antiport

- 3 Na+ ions expelled for every 2K+ ions that enter

Question 29

Na/K+ ATPase important in

Answer 29

generating ion gradient that allows secondary active transport and action potentials
- Note: only small contribution to resting membrane potential

Question 30

Na/K+ ATPase only has a small contribution to

Answer 30

resting membrane potential

Question 31

how much of basal metabolic rate used for pump

Answer 31

25%

Question 32

Na/K+ ATPase is what type fo ATPase

Answer 32

P-type

- ATP phosphorylates asparate, producing phosphoenzyme intermediate

Question 33

structure of Na/K+ ATPase

Answer 33

alpha and B subunit

Question 34

Alpha subunit

Answer 34

• K+
• NA+
• ATP
• ouabain binding site

Question 35

B subunit

Answer 35

• glycoprotein directs pump to surface

Question 36

how does Na/K+ ATPase effect membrane potential

Answer 36

• Sodium pump creates high intracellular [K+]
• K+ diffusion through channels is mainly responsible for membrane potential (-70mV_
• Sodium pump only generates -5-10m through electrogenic pump activity

Question 37

sodium glucose cotransport an example of

Answer 37

secondary active transport

Question 38

sodium glucose cotransport

Answer 38

ATP used to indirectly drive transport

• Entry of Na+ provides energy for the entry of glucose against its concentration gradient
• Sodium transported with glucose via symport
• Without sodium glucose would not be pushed into cell

Question 39

calcium transport (2)

Answer 39

1) Ca2+-Mg2+ ATPase

2) Na+-Ca2+ exchanger (antiport

Question 40

Ca2+-Mg2+ ATPase

Answer 40

a. High affinity

b. Low capacity

Question 41

Na+–Ca2+ exchanger (antiport)

Answer 41

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

a. Low affinity
b. High capacity

Question 42

Na+/ H_ exchanger

Answer 42

– Inward flow of Na down its concentration gradient

leads to cell alkalinisation by removing H+ (antiport)

Question 43

transporters in CF

Answer 43

• Chloride channel mutated- prevents transport of protein after synthesis (CFTR)
• Means water cannot follow chloride into the lumens
• Sticky, thick mucus that will damage organs such as the lungs, GI tract, vas deferens, can plug cervix

Question 44

transporters in vibrio cholera infection

Answer 44

• Over-active Chloride channel
• Increase in Protein kinase A
  o Hyperphosphorylation of chloride channels
• Water follows  Diarrhea

Overall ion transport must create an electroneutral environment
e.g. as many K+ are being pumped in as out