Structure of plasma Membrane- Composed of Phospholipid Bilayer, also contain glycolipid and cholesterol.

Fluid Mosaic Model-Proposed by J. Singer and G. Nicolson-Membranes as 2-dimensional fluids in which protein are inserted into lipid bilayers.

Two Classes of Membrane Protein: 1. Peripheral Membrane Proteins disassociate from membrane following treatmnet with polar reagents. Not inserted into hydrophobic interior of lipid bilayer but rather associated with membrane through protein-protein interaction. which frequently involve ionic bonds (could be disrupted by high pH, high salt concentration.

2. Integral Membrane Protein-Transmembrane protein-span lipid bilayerwith portion exposed on both sides of membrane.

Well studied Integral Membrane Protein in RBC: Glycoporin-131 amino acid, a single transmembrane alpha helix, Oligosaccharides attached to 16 sites on the extracellulor portion of polypeptide chain.

Band 3 Protein-929 amino acid, multiple transmembrane alpha helices, cross membrane 14 times.

Porin: Bacterial transmembrame Protein that cross the membrane as Beta barrel instead of alpha helix.

Proteins that are anchored in plasmamembrane by lipids and glycolipids-The lymphocytes protein Thy-1

GPI Anchors-Protein that are inserted into the outer leaflet of the plasma membrane by glycosylphosphotidyl-inisotol (GPI) anchors.

Glycocalyx- The cell surface covered by the carbohydrate coat which are formed by the oligosaccharides of glycolipids and transmembrane glycoprotein.

It protect cell surface and the oligosaccharides of the glycocalyx servr as markers for a variety of cell cell interaction.

1. Diffusion: 1. Passive-Small hydrophobic molecule, H2O and CO2 cross the phospholipid bilayer witout input of energy.

2. Facilitated Diffusion-Passage of molecules mediated by a carrier protein or channel protein which allow polar and charged molecules to cross the membrane without interacting with the hydrophobic core of the membrane.

Ion Channel- Mediate rapid passage of selected ions across membrane. In nerve and Muscle cells ion channels are responsible for rapid transmission of electrical signals.

1. Voltage gated ion Channel- Opens in response to changes in the electrical potential across plasma membrane. Na⁺ , K+ , Ca 2+ Channel are families of voltage gated ion channel.
2. Ligand Gated Ion Channel-Open in response to neurotransmitters or other signalling moleculed binding to the cell surface receptors.

Patch Clamp technique- A technique to study activity of individual ion channel. A micropipette with a tip diameter of 1 um is used to isolate a small patch of plasmamembrane. Electrical stimuli are then transmitted from within the micropipette and then studying the behavior of the trapped ion channel.

ATP hydrolysis drive the transport of molecules against their electro-chemical gradient. Na+-K+ pump (also called Na+-K+ ATPase). 1. This pump plays a critical role in establishing Na+ and K+ gradient for the propagation of electrical signal in nerve and muscle cells. 2. Na+ gradient established by the pump is also utilized to drive the active transport of a variety of other molecules. 3. In most animal cells it maintains osmotic balance and cell volume.

Active Transport Driven By Ion Gradient-Ion gradient are often used as a source of energy to drive the active transport of other molecules. Epithelial cell lining the intestine carries out active transport by using Na+ gradient.

The process by which cell take up macromolecules and particles from the surrounding medium.

Phagocytosis-Cell engulf large particles (bacteria, cell debris, intact cells). Binding of the particles to receptors on the surface of the phagocytic cell triggers the extension of pseudopodia (composed of actin contractle system).

Pinocytosis-Uptake of material dissolve in fluid.

Receptor Mediated Endocytosis-Only selective uptake of specific molecules. Molecules to be internalized first bind to a specific cell surface receptors which are concentrated to a in specialized regions of plasma membrane known as clathrin-coated pits. These pits buds from the membrane to form small clathrin coated vesicles containing the receptors with the bound ligands. Example- Uptake of Cholesterol by mammalian cells.

LDL- Each particle has about 1500 molecules of cholesteryl- esters in an oily core.The core contain 500 molecules of cholesterol + 8—molecules phospholipid + one molecule of Apoprotein B100.

Protein Traffiking in Endocytosis:

Molecules taken up by endocytosis are transported to endosome, where they are sorted for recycling to the plasma membrane or degradation in lysosome.

Bacterial Cell Walls-The Principal component of bacterial cell walls is a peptido-glycan consisting of polysacchride chains crosslinked by short peptides.

Plant Cell Walls- Cell walls of fungi, algae, and higher plants are made up of cellulose (fibrous polysaccharides) embededded in a gel like matrix of polysaccharides and proteins.

Extracellulor Matrix-Animal cells in tissues are surrounded by an extracellulor matrix consisting of secreted proteins and polysaccharides. Cell surface receptors bind to the extracellulor matrix and anchor the cytoskeleton cell matrix junction.

CELL ADHESION PROTEINS- Four group of cell adhesion proteins are involved in selective cell cell interaction. These proteins are: selectins, integrins, immunoglobulin superfamily members, and cadherins. Cadherins link cytoskeletons of neighboring cells and forms stable cell celljunctions.

Tight Junction-Interaction between strands of transmembrane protein on adjacent cells are responsible for tight junction formation. It prevents the free passage of molecules between epithelial cells and separate the epical and basolateral domains of the plasmamembrane.

Gap Junction-Provide direct connection between cytoplasm of adjacent cells. Transmembrane protein connexion construct gap junction, providing an open channel through plasma membrane which allows ions and small molecules to diffuse freely between adjacent cells. Most animal tissue cells including epithelial cells, endothelial cells, cardiac and smooth muscle cells communicate by gap junction.

Plasmodesmata- When adjacent plant cell communicate with each other through cytoplasmic connections. Plasmamembranes of neighboring cells are continuous forming cytoplasmic channels by an extension of endoplasmic raticulum usually passing through the channel.