lec 5- membrane transport

Question 1

what does diffusion require?

Answer 1

concentration and membrane permeability

Question 2

what molecules pass through the membrane?

Answer 2

small non polar molecules

Question 3

what are the four ways to transport in the membrane?

Answer 3

diffusion, simple diffusion with ion channels, facilitated diffusion, and active transport

Question 4

what is the difference between passive and active transport?

Answer 4

-passive is the transport of molecules down the concentration without the need of energy
-active is the transport of molecules against the concentration gradient with the help of energy

Question 5

what are the molecules that can diffuse through the membrane?

Answer 5

oxygen, CO2 and ethanol

Question 6

what are examples of simple diffusion with ion channels?

Answer 6

voltage-gated ion channels, ligand-gated ion channels, mechano-gated ion channels

Question 7

what are voltage gated, ligand gated, and mechano gated channels?

Answer 7

-voltage gated channels are channels that move ions down the electrochemical gradient
-ligand gated channels require the binding of a ligands to cause conformational change in channel to open
-mechano gated channels require mechanical forces (tension) to cause a conformational change and open

Question 8

does Na+ coordinate as well as K+ with oxygen atoms in the channel?

Answer 8

no

Question 9

what is cystic fibrosis?

Answer 9

cystic fibrosis is a disorder where the chloride channels become defective due to abnormal fluid secretions by the tissues. Mainly cause by mutated genes encoding ion channels

Question 10

explain the facilitated diffusion example known as glucose uniporter:

Answer 10

1. glucose binds to the GLUT1 transporter when its open to the outside of the cell (T1 conformation)
2. glucose causes the GLUT1 transporter to change conformation to T2, causing it to close from outside and open from inside
3. glucose is released into the cell
4. release of glucose causes conformational change back to T1 and repeat of cycle

Question 11

what is the velocity when there is a low extracellular glucose concentration and a high extracellular glucose concentration?

Answer 11

low extracellular glucose concentration means quicker velocity of glucose to go outside, high extracellular glucose concentration means slower velocity to go outside, resulting in a hyperbolic rate

Question 12

what is Vmax?

Answer 12

when an enzyme becomes saturated with its substrate

Question 13

what is Km?

Answer 13

the halfway point of when an enzyme becomes saturated with its substrate

Question 14

what does a low and high Km value mean?

Answer 14

low Km mean good uptake of substrate, while high Km means bad uptake of substrate

Question 15

what does GLUT4 protein do?

Answer 15

stimulated by insulin which increases the rate of glucose uptake into muscles and adipose tissue when glucose concentrations are high so it can be regulated to a lower rate

Question 16

explain the steps to glucose regulation via GLUT4 and insulin?

Answer 16

1. glucose transporters stored within cell in membrane vesicles
2. insulin binds to insulin receptor causing glucose vesicles to attach to membrane increasing the amount of glucose transporters
3. when insulin levels drop, glucose transporters are removed from membrane and go back into vesicles
4. smaller vesicles fuse with large endosome
5. patches of large endosome bud off to create smaller vesicles and cycle continues

Question 17

what is active transport?

Answer 17

like facilitated diffusion, requires proteins that undergo a conformational change to move molecules against the gradient with the help of ATP. proteins are known as pumps

Question 18

what does the sodium-potassium pump do?

Answer 18

lets three Na+ out and 2 K+ in to maintain membrane potentials

Question 19

what is the sarcoplasmic reticulum?

Answer 19

it is a specialized type of ER that forms a network of tubular sacs that store calcium

Question 20

what does Ca2+ pumps do?

Answer 20

keep intracellular Ca2+ concentrations low

Question 21

what is primary and secondary active transport?

Answer 21

primary uses ATP to move molecules while secondary uses that chemical gradient to move other molecules while at it

Question 22

explain glucose Na+ symporter?

Answer 22

when the sodium potassium pump is moving sodium from gut lumen via a symporter to outside of cell to undergo active transport, glucose also comes in by the symporter into the intestine and then through the glucose transporter to get into circulation