Membrane Structure and Function

Page
7

The sodium-potassium pump is one type of active transport system

Slide 53

Fig. 7-16-1

EXTRACELLULAR

FLUID

[Na+] high

[K+] low

Na+

Na+

Na+

[Na+] low

[K+] high

CYTOPLASM

Cytoplasmic Na+ binds to

the sodium-potassium pump.

1

Slide 54

Na+ binding stimulates

phosphorylation by ATP.

Fig. 7-16-2

Na+

Na+

Na+

ATP

P

ADP

2

Slide 55

Fig. 7-16-3

Phosphorylation causes

the protein to change its

shape. Na+ is expelled to

the outside.

Na+

P

Na+

Na+

3

Slide 56

Fig. 7-16-4

K+ binds on the

extracellular side and

triggers release of the

phosphate group.

P

P

K+

K+

4

Slide 57

Fig. 7-16-5

Loss of the phosphate

restores the protein’s original

shape.

K+

K+

5

Slide 58

Fig. 7-16-6

K+ is released, and the

cycle repeats.

K+

K+

6

Slide 59

2

EXTRACELLULAR

FLUID

[Na+] high

[K+] low

[Na+] low

[K+] high

Na+

Na+

Na+

Na+

Na+

Na+

CYTOPLASM

ATP

ADP

P

Na+

Na+

Na+

P

3

K+

K+

6

K+

K+

5

4

K+

K+

P

P

1

Fig. 7-16-7

Slide 60

Fig. 7-17

Passive transport

Diffusion

Facilitated diffusion

Active transport

ATP

Slide 61

How Ion Pumps Maintain Membrane Potential

Membrane potential is the voltage difference across a membrane

Voltage is created by differences in the distribution of positive and negative ions

Slide 62

Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane:

A chemical force (the ion’s concentration gradient)

An electrical force (the effect of the membrane potential on the ion’s movement)

Slide 63

An electrogenic pump is a transport protein that generates voltage across a membrane

The sodium-potassium pump is the major electrogenic pump of animal cells