Membrane transport processes Flashcards Preview

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Flashcards in Membrane transport processes Deck (21):
1

Membrane transport mechanisms

-Pores
-Ion channels
-Solute carriers
-Pumps (ATP dependent)
-Vesicular transport

2

Types of facilitated diffusion

Two types; channel mediated (pores), carrier-mediated (binding)

3

Differences between facilitated diffusion and simple diffusion

-facilitated diffusion can be saturated as limited no. of channel proteins, simple diffusion depends linearly on solute conc.
-facilitated diffusion more temp dependent as temp changes protein composition
-facilitated diffusion far more efficient

4

Water permeability of membranes

Low H2O permeability: ascending loop of Henle
High H2O permeability: red blood cells
Depends on:
-Lipid composition (unsaturated phospholipids increase membrane fluidity -> more permeable to water) (sterol content -> decrease fluidity & water permeability)
-water pores: aquaporins (more important factor)

5

Aquaporins

-Consist of 4 subunits (tetrameric)
-Fast transport rate: 10^9 molecules/sec
-6 a-helical domains form pore -> 4 pores form aquaporin
-Some pores also permeable to small molecues (e.g. glycerol) -> aquaglyceroporins
-Almost always completely open


6

Main method of control for aquaporin permeability

-Ion channels -> change osmolality inside or outside of cell
-Also effected by pH

7

What are ion channels gated by?

-Membran voltage
-Extracellular messengers
-Intracellular messengers
-Mechanical stress (i.e. stretch mediated Na+ channels)

8

Solute carriers operating principle

1. Binds solute on one side of membrane
2. Protein undergoes conformational change
3. Release solute on other side of membrane
-Only allows 1 molecule at a time
-2 conformational changes

9

Difference between channels and carriers

Both allow facilitated diffusion (passive), but:
-Ion channel has central pore
-Solute carrier undergoes conformational change (slower and less efficient)

10

Primary active transport

Hydrolysis of ATP to generate energy for transport

11

Types of ATPase ion transporters

-P-type
-V-type
-F-type

12

P-type ATPase ion transporter

-e.g. Na+/K+ATPase
-ATP hydrolysis leads to phosphorylation causing conformational change

13

V-type ATPase ion transporter

-Vacuolar-type H+ATPase
-Contributes to set up of pH gradients

14

F-type ATPase ion transporter

-F-ATPase or ATP synthase (mitochondria)
-Uses proton gradient for ATP synthesis

15

Na+/K+-ATPase (Na+/K+ pump) structure

4 main domains:
-N nucleotide (ATP) binding domain
-P phosphorylation domain
-A actuator domain
-M transmembrane domain

16

Na+:K+ transmembrane protein transport ratio

3 Na+ out of cell : 1 K+ into cell

17

ABC transporters

Different types for transport of wide range of complex molecules i.e. Cl- and organic anions
-> Good at low concentrations

18

ABC transporter common features

-ATP-binding cassette (ABC)
-Usually homodimer (2 identical subunits)
-Each subunit consists of; transmembrane domain, nucleotide binding domain

19

ABC transporter mode of action

1. Open dimer has high ligand affinity
2. Ligand binding increases ATP affinity -> ATP binding
3. Conformational change -> reduces ligand affinity, ligand releases
4.ATP hydrolysis and release -> return to open configuration

20

Types of co-transport

-Symporters- both solutes are transported in same direction
-Antiporters- solutes are transported in opposite directions

21

Co-transport

-Movement of solute A down its electrochemical gradient can be used to drive co-transport of solute B against electrochemical gradient -> secondary active transport
-Not directly coupled to ATP hydrolysis