Chapter 5a

Chapter 5a

Membrane Dynamics

About this Chapter

• Mass balance and homeostasis• Diffusion• Protein-mediated, vesicular, and

transepithelial transport• Osmosis and tonicity• The resting membrane potential• Insulin secretion

Mass Balance in the Body

Figure 5-2

(through intestine,lungs, skin)

(by kidneys, liver,lungs, skin)

BODYLOAD

Metabolicproduction

Metabolism toa new substance

Mass balance Existingbody load

Law of Mass Balance

+Intake ormetabolicproduction

Excretion ormetabolicremoval

= –

Intake Excretion

Mass Balance and Homeostasis• Clearance • Rate at which a molecule

disappears from the body• Mass flow = concentration

volume flow• Homeostasis equilibrium• Living things not EQ across

membranes• Osmotic equilibrium• Where?

• Chemical disequilibrium• Electrical disequilibrium• Where?

Homeostasis

Figure 5-3a

Homeostasis vs Equlibrium

Figure 5-3b

Compare: ECF vs ICFI vs P

Figure 5-4

Diffusion• Map of membrane transport• Active vs Passive

Uses energy ofmolecular motion.

Does not require ATP

Diffusion

Simplediffusion

Facilitateddiffusion Phagocytosis

Exocytosis

Endocytosis

Secondaryactive

transport

Primaryactive

transport

PHYSICAL REQUIREMENTS

Mediated transportrequires a

membrane protein

Moleculegoes throughlipid bilayer

Uses amembrane-bound

vesicle

Requires energyfrom ATP

ENERGY REQUIREMENTS

MEMBRANE TRANSPORT

createsconcentration

gradientfor

Diffusion: Seven Properties1. Passive process2. High concentration to low

concentration3. Net movement until concentration

is equal4. Rapid over short distances5. Directly related to temperature• How?

6. Inversely related to molecular size7. In open system or across a

partition• Membrane – composition related

to function

Simple Diffusion

Figure 5-5

Figure 5-6

Simple Diffusion

• Fick’s law of diffusion

Rate of diffusion surface area • concentration gradient • membrane permeability

membrane thickness

Extracellular fluid

Membranesurface area

Intracellular fluid

Compositionof lipid layer

Lipidsolubility

Molecularsize

Concentrationoutside cell

Concentrationinside cell

Membranethickness

Concentrationgradient

Fick's Law of Diffusion says:

lipid solubilitymolecular size

Membrane permeability

Membrane permeability

Changing the composition of the lipid layer can increase or decrease membrane permeability.

Simple Diffusion

Table 5-1

Functions of Membrane Proteins

• Structural proteins• Enzymes• Membrane receptor proteins• Transporters• Channel proteins• Carrier proteins

Membrane Transport Proteins

Figure 5-7

MEMBRANEPROTEINS

Integralproteins

Lipid-anchoredproteins

Peripheralproteins

Membranetransporters

Structure

are found in

form

are active in

are active in

activate

changeconformation

Carrierproteins

Channelproteins

Cell junctions

Gated channelsOpen channels

Cytoskeleton

Function

Structuralproteins

Membraneenzymes

Signaltransfer

Metabolism

Receptor-mediated

endocytosis

Chemicallygated

channel

Voltage-gatedchannel

Mechanicallygated

channel

can be categorized according to

open andclose

Membranereceptors

Membrane Transport Proteins

Figure 5-8

Ligand binds toa cell membrane receptor protein.

Receptor

Ligand-receptor complextriggers intracellular response.

Events in the cell

Extracellularfluid

Intracellular fluid

Cell membrane

Membrane Transport Proteins

Figure 5-9

MEMBRANE TRANSPORTERS

Channel proteins create a water-filled pore Carrier proteins never form an open channel betweenthe two sides of the membrane

can be classifiedcan be classified

Gated channels Open channels Uniport carriers Antiport carriersSymport carriers

Cotransporters

ECF

ICF

Cellmembrane

Carrier opento ICF

Same carrieropen to ECF

Open Closed

Membrane Channel Proteins

Figure 5-10

Channel Channel

One proteinsubunit

of channel

Gating of Channel Proteins

Figure 5-11

Membrane

PacificOcean

AtlanticOcean

PacificOcean

AtlanticOcean

PacificOcean Atlantic

Ocean

Closed gate

Transitionstate withboth gates

closed

Passageopen toone side

Passageopen to

other side

Intracellular fluid

Moleculeto betransported

Gate closed

Gate closed

Carrier

Extracellular fluid

(a) (b)

Chemically, voltage or mechanically controlled

Facilitated Diffusion of Glucose

Figure 5-12

Primary Active Transport

Primary Active Transporters • ATPases

• Na/K pump• Ca

Secondary Active Use potential energy

• Na+ glucose• SGLT

Figure 5-14

2 K+ fromECF bind

ADP

ATP

ATPase is phosphorylatedwith Pi from ATP.

Protein changesconformation.

ICF

ECF

Protein changesconformation.

2 K+ releasedinto ICF

3 Na+ fromICF bind

3 Na+ releasedinto ECF

1

2

34

5

Primary Active Transport

• Mechanism of the Na+-K+-ATPase

Primary Active Transport

Figure 5-14, step 1

ICF

ECF

3 Na+ fromICF bind

1

Primary Active Transport

Figure 5-14, steps 1–2

ADP

ATP

ATPase is phosphorylatedwith Pi from ATP.

ICF

ECF

3 Na+ fromICF bind

1

2

Primary Active Transport

Figure 5-14, steps 1–3

ADP

ATP

ATPase is phosphorylatedwith Pi from ATP.

Protein changesconformation.

ICF

ECF

3 Na+ fromICF bind

3 Na+ releasedinto ECF

1

2

3

Primary Active Transport

Figure 5-14, steps 1–4

2 K+ fromECF bind

ADP

ATP

ATPase is phosphorylatedwith Pi from ATP.

Protein changesconformation.

ICF

ECF

3 Na+ fromICF bind

3 Na+ releasedinto ECF

1

2

34

Primary Active Transport

Figure 5-14, steps 1–5

2 K+ fromECF bind

ADP

ATP

ATPase is phosphorylatedwith Pi from ATP.

Protein changesconformation.

ICF

ECF

Protein changesconformation.

2 K+ releasedinto ICF

3 Na+ fromICF bind

3 Na+ releasedinto ECF

1

2

34

5

Figure 5-15

Secondary Active Transport

• Mechanism of the SGLT Transporter

[Na+] low[glucose] high

SGLT protein

Lumen of intestineor kidney

Intracellular fluidGlucose binding changescarrier conformation.

Na+ binds to carrier.

[Na+] high[glucose] low

Na+ binding createsa site for glucose.

Na+ released into cytosol. Glucose follows.

13

4

2

Secondary Active Transport

Figure 5-15, step 1

1

[Na+] low[glucose] high

[Na+] high[glucose] low

SGLT protein

Lumen of intestineor kidney

Intracellular fluid

Na+ binds to carrier.

Secondary Active Transport

Figure 5-15, steps 1–2

1

[Na+] low[glucose] high

[Na+] high[glucose] low

SGLT protein

Lumen of intestineor kidney

Intracellular fluid

Na+ binding creates a site for glucose.

Na+ binds to carrier.

2

Secondary Active Transport

Figure 5-15, steps 1–3

1

[Na+] low[glucose] high

[Na+] high[glucose] low

SGLT protein

Lumen of intestineor kidney

Intracellular fluidGlucose binding changes carrier conformation.

Na+ binding creates a site for glucose.

Na+ binds to carrier.3

2

Secondary Active Transport

Figure 5-15, steps 1–4

1

[Na+] low[glucose] high

[Na+] high[glucose] low

SGLT protein

Lumen of intestineor kidney

Intracellular fluidGlucose binding changes carrier conformation.

Na+ released into cytosol. Glucose follows.

Na+ binding creates a site for glucose.

Na+ binds to carrier.3

4

2