cell and molecular On the Plasma membrane .pptx

Cell and Molecular

1. Presented To : Ma’am Nousheen Presented By: Ali Hamza

2. TOPIC PLASMA MEMBRANE

3. Discovery and Definition Discovery: The cell membrane was discovered by Swiss botanist Carl Naegeli and C. Cramer in 1855.  Plasma membrane is present in all types of cells . It is a boundry that separates the interior of cell from outside environment. Definition: Plasma membrane can be defined as a biological membrane or an outer membrane of a cell, which is composed of two layers of phospholipids and embedded with proteins.

4. Chemical Composition Lipids : Four major classes of lipids are commonly present in the plasma membrane. Phospholipids Sphingolipids Glycolipids Sterols ( e.g Cholesterol) All of them are amphipathic . Proteins : Proteins of the plasma membrane are of two types. Integral Proteins Peripheral Proteins Plasma membrane also contains structural proteins, transport proteins and enzymes.

5. Structure and Model Fluid Mosaic Model This model was given by SINGER and NICOLSON in the year 1972. The  fluid mosaic model  describes the structure of a cell membrane. The plasma membrane is a mosaic of phospholipids, cholesterol molecules, proteins and carbohydrates. Phospholipids: Phospholipids make up the basic structure of a cell membrane. A single phospholipid molecule has two different ends. Head Tail The head end contains a phosphate group and is  hydrophilic . This means that it likes or is attracted to water molecules. The tail end is made up of two strings of hydrogen and carbon atoms called  fatty acid chains . These chains are  hydrophobic , or do not like to mingle with water molecules.

6. The phospholipids of a cell membrane are arranged in a double layer called the  lipid bilayer . The hydrophilic phosphate heads are always arranged so that they are near water. Watery fluids are found both inside a cell ( intracellular fluid ) and outside a cell ( extracellular fluid ). The hydrophobic tails of membrane phospholipids are organized in a manner that keeps them away from water.

7. Cholesterol : Cholesterol molecules are made up of four rings of hydrogen and carbon atoms. They are hydrophobic and are found among the hydrophobic tails in the lipid bilayer. Cholesterol molecules are important for maintaining the consistency of the cell membrane. Cholesterol molecules also keep the phospholipid tails from coming into contact and solidifying. This ensures that the cell membrane stays fluid and flexible.

8. Movement of molecules across plasma membrane Diffusion : Spontaneous movement of particles from an area of high concentration to an area of low concentration. Does not require energy. Equilibrium is reached. Facilitated Diffusion Allows diffusion of large, membrane insoluble compounds such as sugars and amino acids. Does not require energy (passive) Highly Selective Active Transport : Movement across membrane against concentration gradient. Movement from low to high concentrations. Energy used for this movement is provided by ATP .

9. Fluidity of Plasma Membrane A membrane is primarily held together by hydrophobic interactions ,which are much weaker than covalent bonds. Phospholipids in the plasma membrane can move within the bilayer. Most of the lipids and some proteins drift laterally. Rarely does a molecule flip flop transversely across the membrane. The lateral movement of phospholipids is rapid. As the temperature cool, membranes switch from a fluid state to a solid state.

10. Factors affecting Fluidity of Plasma membrane

11. Temperature effect . Cholesterol effect. Functions Permeability barrier. Transport of substances. Signal transduction Enzymatic activity.