Presented by- MADHULIKA NAMDEO

M.Sc. LIFE SCIENCE 1st semester CENTRAL UNIVERSITY OF

GUJRAT, INDIA

Essential for all cells. Surrounding each of our cells is a membrane called

the plasma membrane. The plasma membrane is a continuous double-layer of phospholipids, interweaved with cholesterol and proteins.

Encloses the cell and defines its boundaries. Maintain the essential differences between the cytosol and

extracellular environment. About 5-8nm thickness. It is dynamic and fluid structure. Plasma membranes are selectively permeable, regulating

the cell’s molecular traffic.

Plasma membrane

In 1925, two Dutch scientists E. Gortor and R. Grende poved that PM contain lipids.

Then they extracted the membrane lipids from a known number of blood cells, corresponding to know surface area occupied by a monolayer of the extracted lipid spread out at an air-water interface.

The surface area of lipid monolayer turned out to be twice that occupied by the erythrocyte PM.

This leads to the conclusion that the membranes consist of lipid bilayers rather than monolayer.

PM is a bilayer.

This model was proposed in 1972, S. J. Singer and

Garth Nicholson presented the fluid mosaic model of the cell membrane, which displayed the cell membrane as an integration of proteins and other molecules into the phospholipid bilayer.

The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it.

The cytoskeleton is attached to the cell membrane for added stability, since membrane proteins and phospholipids can shift places in the membrane

Fluid mosaic model

Fluid-Mosaic Model

The structural framework of

PM

Phospholipids are made up of a glycerol backbone with a hydrophilic head region containing a phosphate group and a hydrophobic tail region containing a saturated fatty acid and an unsaturated fatty acid.

Asymmetrically distributed.

Phospholipids

Phosphatidylcholine

Sphingomyelin

Phosphatidyleserine

Phosphatidylinositol

Phosphatidylethanolamine

Types of phospholipids

A membrane is a collage of different proteins

embedded in the fluid matrix of the lipid bilayer

Proteins determine most of the membrane’s specific functions

Integral proteins- located in lipid bilayer, penetrate the hydrophobic core and often span the membrane and are called transmembrane proteins.

Peripheral proteins are not embedded in bilayer, can found on either surface of the bilayer.

Membrane protein

Types of protein

Fluidity

Membranes are maintained by hydrophobic interactions of the phospholipids resulting in the alignment of the polar phosphate regions toward the aqueous environment and the nonpolar regions’ hydrocarbon chains toward each other.

Membrane fluidity may be influenced by presence/absence of unsaturated FA chains and Cholesterol

Membranes are in motion with fast drifting lipids and slower drifting proteins.

Fluidity Influences Permeability Permeability deals with the movement of materials

across a membrane

The hydrophobic portion of the lipid bilayer is selectively permeable; allowing only certain substances to cross.

Cholesterol reduces the permeability of membrane because it fills the space of bilayer, but It also allows the cell membrane to stay fluid over a wider range of temperatures.

Combination of proteins makes membrane unique

Membrane proteins may be fluid or anchored.

Proteins may penetrate the bilayer fully (integral) and involve in cell to cell signaling with surface carbohydrate chains or linking with the cytoskeleton for support.

or reside on the surfaces of membranes (peripheral).

Integral proteins typically have hydrophobic regions that span the bilayer as a result of nonpolar amino acids arranged as helices.

Anchored proteins strengthen membranes.

Mosaic

The cell membrane is the outer most layer of the cell,

and its functions are as follows: - Allows certain materials to enter the cell - Gets rid of cell waste. - Contains all the cell organelles. - Protects the cell from injury

Function of plasma membrane

Functions of phospholipids:

Act as building blocks of the biological cell membranes in virtually all organisms

Participate in the transduction of biological signals across the membrane.

Play an important role in the transport of fat between gut and liver in mammalian digestion.

Function of phospholipids

Cholesterol maintains the integrity of the cell

membrane

Cholesterol helps maintain the fluidity of cell membranes

Cholesterol helps secure important proteins in the membrane

Carbohydrates often attach to the external surface of integral proteins. These carbohydrates may hold adjoining cells together or act as sites with chemical messengers such as hormones can attach

Cholesterol and carbohydrate

Six major functions of membrane proteins: Transport

Enzymatic activity

Signal transduction

Cell-cell recognition

Intercellular joining

Attachment to the cytoskeleton and extracellular matrix (ECM)

Function of membrane protein

A transport protein is specific for the substance it

moves.

Transport proteins allow passage of hydrophilic substances across the membrane.

Channel protein- have a hydrophilic channel that certain molecules or ions can use as a tunnel.

Also called aquaporins and facilitate the passage of water.

Carrier proteins- bind to molecules and change shape to shuttle them across the membrane.

Transporter protein

Channel protein Carrier protein

Alzheimer's Disease- The oxidative stress caused altercation in phospholipids. disrupting the function of the brain cells. Cystic Fibrosis- due to a defective calcium-ion channel The calcium-ion channel controls the level of fluids and

mucus in our lungs Duchenne Muscular Dystrophy- This disease affects dystrophin in the muscle cell. Cell become incapable of repairing itself.

Disease

It segregate and protect form the environment.

Fluid mosaic model deals with fluidity and permeability.

Fluidity is facilitated by phospholipids composition.

Fluidity of membrane makes it unique .

Maximum of the function is done by membrane bound proteins.

Membrane dysfunction leads to diseased condition.

Summary