DR. LEENA N. MESHRAM

1. Mahatma Phule A. S. C. College, Panvel DEPTARTMENT OF ZOOLOGY DR. LEENA N. MESHRAM

2. PLASMA MEMBRANE AND TRANSPORTATION PROCESS

3. General Function of Plasma Membrane • Protects the whole cell • Separates the cell components from its environment • Regulates transport of molecules in and out of the cell • Controls the intake of foreign molecules due to its selective permeable characteristics.

4. Plasma membrane • A model that described the structure of plasma membrane which consists of various proteins embedded in or attached to a double layer (bilayer) of phospholipids. • In 1935, Hugh Davson and James Danielli suggested a structure of the membrane • - the membrane were coated on both sides with hydrophilic proteins, a sandwich model : a phospholipid bilayer between two layers of proteins

6. In 1972, S.J. Singer and G. Nicholson proposed that membrane proteins are dispersed and individually inserted into the phospholipid bilayer with only their hydrophilic regions protruding far enough from the bilayer to be exposed to water. This structure is called The Fluid Mosaic Model

7. The Fluid Mosaic Model - S.J. Singer and G. Nicholson Carbohydrate covalently bonded to protein. Main functions: cell-cell recognition Carbohydratecovalently bonded to lipid. Proteins that penetrate the hydrophobic core of the lipid blayer. Many are transmembrane proteins which completely span the membrane Not embedded in the lipid bilayer; bound loosely to the surface of the membrane, the exposed part of the integral protein.

8. Permeability of Plasma Membrane • Depends on its structure and pore size • 4 types of permeability: • Permeable • Allows all solutes or molecules to pass through. • Semi-permeable • Allows only water molecules and not solutes to pass through. • Selectively permeable • Allows selected solutes and water to pass through. • Non-permeable • Does not allow solutes or water molecules to pass through.

9. In transportation across the plasma membrane, these elements will be discussed: • 1. Solution • A liquid that is a homogeneous mixture of two or more substances • Solvent • The dissolving agent of a substance. • Water is the most versatile solvent known. • Solute • A substance that is dissolved in a solution

10. Transportation processes across plasma membrane • 1. Passive transport • Movement of materials or molecules through a membrane down the concentration gradient, without the use of energy. • Examples: Diffusion, osmosis and dialysis • Active transport • Involved a carrier system (protein or lipoprotein) to transfer materials or molecules against the concentration gradient, with the use of energy – ATP.

11. Passive transport Diffusion A substance diffuses from where it is more concentrated to where it is less concentrated – the substance will diffuse down its concentration gradient until it reaches equilibrium.

12. Rate of diffusion depends on several factors: • Concentration gradient • The higher the concentration gradient, the higher the rate of diffusion • Diffusion distance • The shorter the diffusion distance, the higher the rate of diffusion. • Surface area of diffusion • The bigger the surface area, the higher the rate of diffusion. • Structure and characteristics where diffusion occurs • Higher number and size of the membrane pores will result in higher diffusion rate. • Size and characteristics of diffused molecules • Lipid-soluble molecules can easily cross the plasma membrane. • The smaller the molecules, the higher the rate of diffusion.

13. Same concentrations of sugar osmosis Only allows water molecules to pass through the pores. • Osmosis • The diffusion of water across the selectively permeable membrane from the region of lower concentration to the higher concentrations until both sides are equal • Passive transport – no energy needed

14. 3 types of environments: Isotonic – the same environment with the cell - no net movement of water across the membrane, but at the same rate in both directions Hypertonic – the environment is more concentrated compared to the cell - the cell will lose water to its environment Hypotonic – the environment is less concentrated compared to the cell - the water will enter the cell

15. Water balance of cells without walls Water balance of cells with walls Hemolysis Normal Crenation Turgid Deplasmolysis Plasmolysis

16. Active transport • The movement of substance across a biological membrane against its concentration gradient with the help of energy input and specific transport protein • ATP power active transport by transferring its terminal phosphate group directly to the transport protein • It could induce the protein to change its shape to help transfer the solute bound to the protein across the membrane • Example: Sodium-potassium pump – an exchange of sodium (Na+) for potassium (K+) across the plasma membrane of animal cells

17. Specific transport protein Less concentration region High concentration region

18. Exocytosis • The cell secretes macromolecules by the fusion of vesicles with the plasma membrane and spill them to the outside of the cell • Many secretory cells use exocytosis to export their products • Example: Cell in pancreas that secretes insulin.

19. Endocytosis • The cell takes in macromolecules and particulate matter by invagination of the plasma membrane. Involved the formation of vacuole which is surrounded by plasma membrane. • Two types of endocytosis: • Phagocytosis (cellular eating) • The intake material is in solid form. • Pinocytosis (cellular drinking) • The intake material is in liquid form.

20. A cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be classified as a vacuole. The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes.

21. The cell gulps droplets of extra-cellular fluid into tiny vesicles. It is not the fluid itself that is needed by the cell, but the molecules dissolved in the droplet. Because any and all included solutes are taken into the cell, pinocytosis is nonspecific in the substances it transport.