L4

Question 1

describe the proteins in protein mediated membrane transport

what do they function as

Answer 1

the span the cell membrane (all the way through)

they function as enzymes as they catalyse the transport of solutes across the membrane

Question 2

in passive transport proteins function as….

Answer 2

channels or carriers

Question 3

passive transport happens through…..

Answer 3

facilitated diffusion and therefore is concentration dependent (high to low)

Question 4

what are the 2 generalised forms of active transport

Answer 4

primary (ATP dependent) and secondary active transport

Question 5

what is secondary active transport

Answer 5

these proteins act as carriers/transporters and they use the down hill gradient of one solute to transport another solute up its concentration graident

Question 6

how selective are the channels and carriers in passive transport

Answer 6

they cover a wide range of selectivity (eg K+ channels are very selective whereas Na+ channels are not)

Question 7

why are the proteins in passive transport selective

Answer 7

because they require an interaction between the substrate and the protein. these proteins also often have a binding site/selectivity filter for that specific solute

Question 8

in passive transport what is the difference between channels and carriers

Answer 8

channels are fast as they usually have a gate and when that gate opens the thing that it is selective for will rush through it

carriers are much slower because they require an interaction and a conformational change of the bratein

Question 9

what is a pore

Answer 9

in is the simplest form of a channel

they are a small selective tunnels through which molecules can move rapidly

Question 10

what do pores typically transport

Answer 10

ions, water (eg aquaporins), small solutes

Question 11

what are channels

Answer 11

they are gated pores that open and close spontaneously

Question 12

pores are a passive mechanism. what does this mean

Answer 12

movement of a solute via a channel is determined by the greadent for the solute

this is both the electrical and chemical greadent (electrochemical)

Question 13

what are the 3 ways that a channel could be named

Answer 13

the obvious way (what it is/descriptive way)

after the diseased state

or after the thing that inhibits it

Question 14

when facilitated diffusion occurs it happens through a gated channel. is this all or nothing

Answer 14

yes

Question 15

what is CFTR

Answer 15

cystic fibrosis transmembrane regulatory protein

it is a Cl- channel (note that this is not a regulatory protein)

Question 16

CFTR is a Cl- channel but it can also let through something else. why is this

Answer 16

it can also let through bicarbonate

this only will happen when bicarbonate is in high concentration

this doesn’t really happen in the body as cells which have CFTR always make sure they have a high concentration of Cl

when it does get in, it does slightly reduce the efficiency for that specific protein but it will have very little overall effect

Question 17

what is the permeability of a membrane to a solute determined by

Answer 17

the number of channels for that solute in the membrane

and

the open probability of the channels in the membrane

Question 18

the fraction of time ligand gated channels stay open/the number of channels is modified by….

Answer 18

ACh and other specific molecules

Question 19

the fraction of time voltage gated channels stay open/the number of channels is modified by….

Answer 19

in the case of membrane potential it is voltage gated Na channels

Question 20

the fraction of time mechanical gated channels stay open/the number of channels is modified by….

Answer 20

mechanical deformation

eg touch receptors and hair cells

Question 21

what is cotransport

Answer 21

when both solutes move in the same direction

also called uniport

Question 22

what is counter transport

Answer 22

when solutes move in the opposite direction

Question 23

what does carrier mediated transport usually transport

Answer 23

ions (Na, K, Cl, HCO3)

other solutes like glucose and amino acids

Question 24

what determines selectivity in carrier mediated transport

Answer 24

binding sites

Question 25

describe the binding sites for protein in carrier mediated transport

Answer 25

it is a turnstyle type system (things at theme parks that only let one person through at a time)

the binding site/s is only accessible from one side of the membrane at a time

it will bind one or 2 molecules and then changes conformation, transporting solute across the membrane

Question 26

what is carrier inhibition

2 reasons

Answer 26

carriers are conducts that are gated by 2 doors that are never open at the same time.

if something were to bind and keep the carrier in an open form that is a inhibitor

it can also be if something with similar characteristics as the selected solute is in a high concentration that that will bind reducing the efficiency of the carrier

Question 27

lol

Answer 27

lol

Question 28

how are carriers defined

Answer 28

in therm of their slute

this could be the solute transported against the electrochemical greident or the binding of the substrates required

Question 29

what are some examples of carriers in primary active transport

Answer 29

Na/K ATPase

H/K ATPase

Question 30

what are some examples of carriers in secondary active transport

Answer 30

SGLT1 (sodium-glucose linked transporter 1)

NHE (NA H exchanger)

AE (Cl -HCO3 exchanger)

anion exchangers

Question 31

what is the rule for how secondary active transporters work

Answer 31

the downhill transport of one solute drives the uphill transport of a second solute

Question 32

cells with CFTR need to have a high intracellular conc of Cl. how do they maintain this

Answer 32

cells with CFTR also have K+ channel, a NaK ATPase and NKCC1

NKCC1 brings Na, Cl and K+ into the cell.

we can’t have a high conc of Na inside the cell otherwise it will burst so Na/K ATPase pumps 3Na out and 2K in

this extra K+ brought in by the Na/K ATPase and NKCC1 is then pumped out of the cell

Question 33

what is NKCC1

Answer 33

Na+ K+ Cl- cotransporter

it requires Na as it used the energy of Na moving down it greadent to being K and CL into the cell

Question 34

what does CFTR do

Answer 34

it transports Cl- into the lumen

without this your gut and lungs would dry up

Question 35

describe the K+ channel in cells with CFTR

Answer 35

it is a uniporter as it recycles K+ into the serosa