Block 2 Lecture 20

Question 1

what are the similarities between carriers and channels

Answer 1

• both are integral membrane proteins

- both move molecules across membranes

Question 2

what is the difference between carriers and channels

Answer 2

all channels and only some carriers can net transport down the electrochemical gradient

Question 3

what happens to saturability at low concentrations

Answer 3

transport increases in almost direct proportion with increase in [S]

Question 4

what happens to saturability at high concentrations

Answer 4

changes in x do not correlate with changes in y, it is zero order

Question 5

what is Jmax

Answer 5

the maximum rate or carrier-mediate transport

Question 6

how do you calculate Jmax

Answer 6

number of transporters times the turnover number

Question 7

what is the michaelis menten equation

Answer 7

• the relationship between substrate concentrations and the rate of transport
• J = Jax [S]/Kt + [S]

Question 8

what is Kt

Answer 8

a constant and is equal to the substrate concentration that produces half maximal transport
-michaelis constant

Question 9

what is J

Answer 9

the rate of transport at a substrate concentration equal to [S]

Question 10

what is the Eadie-Hofstee equation

Answer 10

J = -Kt (J)/[S] + Jmax

Question 11

what is selectivity

Answer 11

the translocation of substrate from one side of the membrane to the other that is mediated by a carrier involves the transient binding of the substrate to a site or surface on the carrier

Question 12

what is competitive inhibition

Answer 12

competition between substrates for a common carrier binding site

Question 13

what happens as a result of competitive inhibition

Answer 13

• rate of substrate transport will be reduced

- if substrate concentration is increased, the normal maximal rate of transport (Jmax) can be achieved

Question 14

what happens to Jmax and Kt as a result of competitive inhibition

Answer 14

an increase in Kt and no change in Jmax

Question 15

what happens as a result of noncompetitive inhibition

Answer 15

no matter how much substrate you add it cannot prevent the noncompetitive inhibitor from binding making fewer transporters but any transporter not bound to an inhibitor is completely normal

Question 16

what happens to Jmax and Kt as a result of noncompetitive inhibition

Answer 16

decrease in Jmax and no change in Kt

Question 17

what is noncompetitive inhibtion

Answer 17

there are binding sites for the inhibitor is separate from the active site where the substrate binds

Question 18

what is Jmax a measure of

Answer 18

the capacity of a transporter to move substrate

Question 19

what is Kt a measure of

Answer 19

the extent to which transport capacity is actually realized under physiological conditions

Question 20

what does a change in Jmax indicate

Answer 20

a change in the number of transporters

Question 21

what does a change in Kt indicate

Answer 21

a change in the structure of a protein

Question 22

what are the two categories of carrier mediated transport

Answer 22

1. process that can only support net movement of substrate molecules down their electrochemical gradient
2. those than can support net movement of substrate molecules against their electrochemical gradient

Question 23

what is facilitated diffusion

Answer 23

a process that cannot support net transport of substrate against an electrochemical gradient

Question 24

what happens with the facilitated diffusion of glucose (3 points)

Answer 24

1. at steady state the maximum concentration of glucose that is achieved in the cell is the same as the concentration outside
2. involved shape of course uptake begins at first order where y depends on x but when influx = efflux the graph is zero order
3. this actually is an example of equilibrium because once influx = efflux there is no inwardly directed glucose gradient anymore

Question 25

what represents steady state

Answer 25

when a time dependent process reaches constancy

Question 26

what reflects saturation

Answer 26

when a concentration dependent process reaches constancy