lecture 22 - transport across cell membranes

Question 1

non-mediated transport

Answer 1

doesn’t use transport protein, substances move directly through the lipid bilayer.

Question 2

mediated transport

Answer 2

requires transport proteins (membrane is otherwise a barrier to this material)

Question 3

passive transport

Answer 3

moves substances down concentration gradient using only their kinetic energy

Question 4

active transport

Answer 4

uses energy to drive substances against concentration gradient or electrochemical gradient

Question 5

vesicular transport

Answer 5

move materials across membrane in small lipid vesicles by either exocytosis or endocytosis

Question 6

transport involved with absorption of nutrients and excretion of waste

Answer 6

non-mediated transport

Question 7

What is transported via “non-mediated transport”?

Answer 7

• non-polar hydrophobic molecules

- e.g. O2, N2, small alcohols, fatty acids, steroids, fat soluble vitamins AEDK

Question 8

fat soluble vitamins are…

Answer 8

A, E, D, and K

Question 9

ion channels are _______ filled pores

Answer 9

ion channels are water filled pores

Question 10

which type of amino acids line the inside and the outside of the ion channels

Answer 10

hydrophobic amino acids coiled into alpha helices on the outside. hydrophilic amino acids on the inside of the channel

Question 11

do the ions interact and bind with the ion channel? what does this allow?

Answer 11

NO, this allows for rapid transport (1million per second)

Question 12

in ion channels what determines direction of the ion flow?

Answer 12

down electrochemical gradient

Question 13

ion selectivity filter = ?

Answer 13

selectivity of the channel to specific ions, achieved using various amino acids. Allows only specific ion gradient’s energy to be harnessed.

Question 14

why do ion channels have gates

Answer 14

if they were always open you would not be able to store energy in ion gradients - they would always equilibriate

Question 15

5 stimuli for opening/closing gates

Answer 15

1. voltage
2. ligand binding
3. cell volume
4. pH
5. phosphorylation

Question 16

patch clamp technique

Answer 16

measures the current travelling through an individual channel. measures ion channel function.

Question 17

diffusion of over 1 _______ ions per second generates current of ____A

Answer 17

diffusion of over 1 million ions per second generates current of _10^-12_A

Question 18

what do current fluctuations indicate

Answer 18

opening and closing of gates

Question 19

main way carrier-mediated transport differs to ion channels. implications?

Answer 19

the substrate being transported binds directly to the channel, inducing a conformational change, meaning the rates of transfer are much slower

Question 20

how are carrier transport proteins like enzymes?

Answer 20

• specificity
• inhibition (covalent bonds form)
• competition (glucose/glactose compete for same site)
• saturation (transport maximum)

Question 21

carrier-mediated can be ______ or _______

Answer 21

carrier-mediated can be Passive or Active

Question 22

passive mediated transport called…

Answer 22

facilitated difsussion

Question 23

3 steps to facilitated diffusion of glucose

Answer 23

1. glucose binds to GLUT
2. Glut changes shape. Glucose moves across cell membrane DOWN concentration gradient
3. Kinase reduces glucose concentration (tranforms to glucose-6-phosphate) otherwise you reach an equilibrium g

Question 24

primary active transport

Answer 24

energy comes straight from the hydrolysis of ATP.

Question 25

what percentage of a cell’s ATP is used for primary active transport?

Answer 25

~30%

Question 26

secondary active transport

Answer 26

energy indirectly comes from ATP (the energy stored in ionic gradients is used)

Question 27

Ca/K ATPase

Answer 27

muscle SR

Question 28

H/K ATPase

Answer 28

stomach acidity

Question 29

electrogenic =

Answer 29

net current generated

Question 30

Na/K ATPase 4 steps

Answer 30

1. Na+ binding
2. ATP hydrolysed, P binds and 3Na+ pushed out
3. K+ binding, P released
4. 2K+ pushed in

Question 31

Na/K ATPase important for

Answer 31

• maintaining resting membrane potential
• electrical excitability
• muscle contraction
• maintain cell volume
• uptake of nutrients via secondary active transport
• pH by secondary active transport

Question 32

Pump-leak hypothesis

Answer 32

Na and K are constantly leaking back in, thus the pump must work consistently

Question 33

Na+ antiporters (or exchanges)

Answer 33

Na+ rushes in causing Ca2+ or H+ to be pushed out

Question 34

Na+ symporters (or cotransporters)

Answer 34

glucose or amino acids (MUST BIND FIRST) then rush inwards together with Na+

Question 35

endocytosis

Answer 35

large particles into the cell. Substance transported is inside a vesicle and therefore doesn’t make contact with the hydrophobic core and whatnot

Question 36

phagocytosis

Answer 36

cell eating - foreign particle binds to receptor proteins. pseudopods extend to form phagosome

Question 37

pinocytosis

Answer 37

cell drinking - no receptor proteins, no pseudopods form, non-selective

Question 38

exocytosis

Answer 38

substances are exported from cells by fusion of vesicle with cell membrane

Question 39

vesicles necessary to…

Answer 39

prevent things from reacting that shouldn’t be e.g. protease in the pancreas

Question 40

neurotransmitters and enzymes transported via

Answer 40

exocytosis

Question 41

receptor-mediated endocytosis for?

Answer 41

uptake of specific substances or LIGANDS

Question 42

receptor-mediated endocytosis steps

Answer 42

1. desired substance binds receptor protein in CLATHERIN-COATED PIT REGION of membrane
2. causes membrane to fold inwards, forms vesicle
3. vesicles become uncoated and bind with ENDOSOME
4. receptor proteins seperate from ligands and return to surface
5. ligands digested by lysosomes or transported across cell