11.10 (dr. husun bano)transport of substances across cell membrane
TRANSCRIPT
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