CELL MEMBRANE

FLUID MOSAIC MODEL

1. MEMBRANE LIPIDS

Phospholipids (75%)DynamicBilayerAmphipathic

* Polar part: phosphate-containg “head”, hydrophilic

* Nonpolar part: two fatty acid “tail”, hydrophobic

MEMBRANE COMPOSITION

Glycolipids (5%)Faces external fluidFor adhesionBacterial toxin targetCell-to cell recognition and communicationContribute cellular growth and development

Cholesterol (20%)Strengthen the membrane, decrease flexibility

2. MEMBRANE PROTEIN FUNCTION

Channel

Transporter

Receptor

Enzyme

Cytoskeleton Anchor

Cell Identify Marker

MEMBRANE PHYSIOLOGY

1. Communication Interaction

• Other cell• Foreign cell, ligands

2. Electrochemical gradient Membrane potential

3. Selective permeability Lipid solubility Size Charge Presence of channel and

transporter

Electrochemical gradient

Membrane potential

- 90 mV

TRANSPORT ACROSS MEMBRANE

1. Simple Diffusion Concentration gradient Net diffusion Equilibrium

2. Osmosis Osmotic pressure Tonicity

- Isotonic- Hypertonic- Hypotonic

3. Bulk Flow Same direction Filtration

4. Facilitated Diffusion Transporter

- Channel

PASSIVE TRANSPORT

FACILITATED DIFFUSION

ACTIVE TRANSPOR

1. Primary active transport

Use ATP as the energy source- Ca2+ pump

- Na+, K+ pump

2. Secondary active transport

Use the ionic concentration difference (gradient)

Symport (co-transport)- Glucose transport

- Amino acid transport

Antiport (counter transport)- Na – Ca exchange- Na – H exchange

Sodium pump (Na+,K+-ATPase

VESICULAR TRANSPORT

1. Phagocytosis Pseudopod phagocytic vesicle (phagosome)

2. Pinocytosis Pinocytic vesicle

3. Receptor-Mediated Endocytosis Similar to pinocytosis Import needed materials

4. Exocytosis

Receptor – mediated endocytosis

1. Ligand binds to receptor

2. Forming endocytic vesicle

3. Merging endocytic vesicle endosome

4. Within the endosome receptor separate from their ligands

5. Endosome containing receptor pinches off and moves back to plasma membrane

6. Endosome containing material merges with lysosome

MEMBRANE POTENTIAL

1. ION CHANNEL

Leakage (non gated) channel- K+ leakage channel > Na+ leakage channel

Gated channel- Voltage-gated (voltage-regulated) ion channel

- Chemically gated ion channel

- Mechanically gated ion channel

- Light-gated ion channel

2. RESTING MEMBRANE POTENTIAL

Polarized membrane

Unequal distribution of ion across membrane

Relative permeability of the membrane to Na+ and K+

• Potassium equilibrium potential (– 90 mV)

2. GRADED POTENTIAL The presence of chemically, mechanically, or light-gated

channel Small deviation from the resting potential that cause by an

appropriate stimulus Have different name, depend on type of stimulation Chemically gated ion channel postsynaptic potential;

sensory receptor receptor potential & generator potential Hyper-polarization & depolarization Most often in dendrite and body cell, less often in axon The electrical sign are graded, depending on the strength of

stimulus Localized current

3. ACTION POTENTIAL

Ionic Mechanism of Action Potential

Propagation (Conduction) of Action Potential

Comparison of graded potential and action potential

Graded Potential Action Potential

Amplitude A variable size (1-50 mV) Same size (100 mV)

Duration Milliseconds – minutes ½ msec. – 2 msec.

Channel Chemical, mechanical & light gated channel

Voltage gated channels

Location Dendrite & Cell body Axon

Propagation Localized Propagate

Refractory period No refractory period Shows

Operation of Chemical Synapse