lecture 22 - transport across cell membranes Flashcards Preview

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Flashcards in lecture 22 - transport across cell membranes Deck (42):
1

non-mediated transport

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

2

mediated transport

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

3

passive transport

moves substances down concentration gradient using only their kinetic energy

4

active transport

uses energy to drive substances against concentration gradient or electrochemical gradient

5

vesicular transport

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

6

transport involved with absorption of nutrients and excretion of waste

non-mediated transport

7

What is transported via "non-mediated transport"?

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

8

fat soluble vitamins are...

A, E, D, and K

9

ion channels are _______ filled pores

ion channels are _water_ filled pores

10

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

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

11

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

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

12

in ion channels what determines direction of the ion flow?

down electrochemical gradient

13

ion selectivity filter = ?

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

14

why do ion channels have gates

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

15

5 stimuli for opening/closing gates

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

16

patch clamp technique

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

17

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

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

18

what do current fluctuations indicate

opening and closing of gates

19

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

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

20

how are carrier transport proteins like enzymes?

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

21

carrier-mediated can be ______ or _______

carrier-mediated can be _Passive_ or _Active_

22

passive mediated transport called...

facilitated difsussion

23

3 steps to facilitated diffusion of glucose

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

24

primary active transport

energy comes straight from the hydrolysis of ATP.

25

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

~30%

26

secondary active transport

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

27

Ca/K ATPase

muscle SR

28

H/K ATPase

stomach acidity

29

electrogenic =

net current generated

30

Na/K ATPase 4 steps

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

31

Na/K ATPase important for

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

32

Pump-leak hypothesis

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

33

Na+ antiporters (or exchanges)

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

34

Na+ symporters (or cotransporters)

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

35

endocytosis

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

36

phagocytosis

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

37

pinocytosis

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

38

exocytosis

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

39

vesicles necessary to...

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

40

neurotransmitters and enzymes transported via

exocytosis

41

receptor-mediated endocytosis for?

uptake of specific substances or LIGANDS

42

receptor-mediated endocytosis steps

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