TRANSPORT OF SUBSTANCES THROUGH CELL MEMBRANE

(PASSIVE DIFFUSION)

Husn BanoAssistant Professor

Deptt PhysiologySindh Medical College ,DUHS

TRANSPORT THROUGH CELL MEMBRANE

TYPES:1. PASSIVE TRANSPORT

• Simple diffusion• Facilitative diffusion• Osmosis

2. Active Transport

• Primary active transport e.g. Co-transport Na+-K+ pump

Secondary active transport

(Counter transport) Na+-H+

continue

3. Endocytsis: Pinocytosis

Phagocytosis

4. Exoytsis

5. Bulk Flow

STRUCTURE OF CELL MEMBRANE

PASSIVE DIFFUSION

DEFINATION:

It is the process through which both solute and solvent molecules move from higher conc. to lower concentration.

TYPES OF PASSIVE DIFFUSION:

1. Simple diffusion

2. Facilitated diffusion

1: SIMPLE DIFFUSION

• Simple diffusion means that molecules move from higher concentration to lower conc. through “PORES” or “INTERCELLULAR SPACE” of cell membrane.

OR

Random movement of molecules from higher to lower concentration.

SIMPLE DIFFUSION

A: SIMPLE DIFFUSION THROUGH LIPID BILAYER

• CO2

• O2

• N2

• ALCOHOL

• H2O……? (molecular size 0.3nm)

TRANSPORT OF H2O AND OTHER LIPID INSOLUBLE SUBSTANCES

• H2O……? (molecular size 0.3nm)

• Like H2O other lipid insoluble substances passes through lipid bilayer, if their molecular size is very small.

B: SIMPLE DIFFUSION THROUGH PROTEIN CHANNAL

• All the water soluble substances except charged particles (electrolytes) passes through protein channels , not through lipid bilayer.

Reason of impermeabilityof charge particles

• They are hydrated ions.

• Outer pole of lipid bilayer have negative charge………

Hydrated Cl- (molecular size 3.6nm)

Protein Transporters

1) Channels 2) Carriers

a) open

b) gated

TRANSPORT THROUGH GATED PROTEIN CHANNELS.

• Sodium (Na+)• Potassium (K+)• Calcium (Ca++)• Chloride (Cl - )

ACTUAL MOLECULAR SIZE / Hydrated Size

Na+ 0.34nm 5.2nm K+ 0.36nm 3.9nm Cl - 0.32nm 0.36nm

MODEL OF SODIUM CHANNEL

FLOW OF POTASSIUM IONS

2: FACILITATED DIFFUSION

Definition: is the transport mechanism which require “CARRIER PROTEIN”

Mechanism:1. Molecule + CARRIER PROTEIN2. Conformational change in carrier protein3. Molecule detached from carrier4. No energy or ATP requried

FACILITATED DIFFUSION

Glucose

Amino acids Other simple carbohydrates such as :

Glactose

Mannose

Arabinose

Xylose.

All require “carrier protein” for their transport, so called “carrier mediated diffusion”

FACILITATED DIFFUSION verses SIMPLE DIFFUSION

• Facilitated diffusion require “CARRIER”

• Facilitated diffusion always have Vmax

Simple diffusion Facilitated diffusion

Factors affecting rate of diffusion

1 Permeability of membrane

2 Concentration difference

3. Pressure difference

4 Electrical difference

Factors Affecting On Permeability of membrane

1.Thickness of membrane

2. Lipid solubility

3 Numbers of protein channels.

4 Temperature

5 Square root of molecular weigh

6 Crossectional area of membrane

Special categories of transport

1. BULK TRANSPORT:

It is the transport mechanism in which large quantity of substances transported from high pressure to low pressure e.g Gases exchange through respiratory membrane

ENDOCYTOSIS

• Large molecule or macromolecules transported by endocytosis.

• Endocytosis are of 3 types

a. Pinocytosis

b. Phagocytosis

c. Receptor mediated endocytosis

PINOCYTOSIS (Cell drinking)

1. Large bacteria or antigen( in the form of droplet fluid) bind with outer

surface of membrane.

2 Cell memb. Evaginate arround the droplets

3 It is detached from cell memb.,forms ENDOSOME.

PINOCYTOSIS (Cell drinking) Cont..

• 4. Primary lysosomse attach with edosome ,converted into secondry lysosomes.

• 5. Hydrolytic enzymes present in secondary lysosome becomes activated and digest the content of endosome

PINOCYTOSIS (Cell drinking)

PHYGOCYTOSIS (Cell eating)

RECEPTOR MEDIATED ENDOCYTOSIS

The End