Cell membrane ppt

cell membrane and transport mechanism

1. CELL MEMBRANE STRUCTURE Anas K P 2 nd yr PBBSc GCNT

2. Objectives Define cell and cell membrane Functions of cell membrane Transport mechanisms of cell membrane

3. CELLS Basic living unit of all organisms. Determine the form and functions of the human body. Are specialized to perform specific functions. Organelles inside the cell perform specific functions. CELL MEMBRANE The cell membrane (also called the plasma membrane) is a biological membrane separating the interior of a cell from the outside environment. It appears in thin sections with the electron microscope as a double layered structure about 7.5 – 10 nanometers thick. It contain almost proteins called membrane proteins.

4. Structure of cell membrane Lipid Bilayer - 2 leyers of phospholipids Phosphate head is polar ( water loving ) Fatty acid tail is non polar ( hydro phobic ) Protein embedded in membrane Chemical composition Lipids : Four major classes of lipids are commonly present in the plasma membrane ; Phospholipids ( most abundant ) , Spingolipids , Glycolipids , and Sterols ( eg : Cholesterol) Proteins : Plasma membrane contains about 50% protein. Amount and type is variable.

5. Myelin cells contains about 25% protein internal membrane of chloroplast and mitochondria contains 50% proteins. Protein of plasma membrane are of two type ectoproteins and endoproteins . Plasma membranes contain structural proteins , transport proteins and enzymes. Carbohydrates : They are present only in the plasma membrane and are present exterior ( glycoprotein's ) or polar end of phospholipids at the external surface of plasma membrane.

6. Phospholipids : Phospholipids (PL) molecule has a polar head and non polar tails. The polar head is charged and hydrophilic ( loves water ) facing outward , contains a - PO4 group and glycerol. The non polar tails are hydrophobic ( water hates ) facing inward contain 2 fatty acid chains that are nonpolar . When Phospholipids placed in water form bilayer .

7. Functions of cell membranes: Protective function Selective permeability Absorptive function Excretory function Exchange of gases Maintenance of shape and size of the cells

8. Transport Mechanisms The permeability of substances across cell membranes is dependent on their solubility in lipids and not on their molecular size. Water soluble compounds are generally impermeable and require carrier mediated transport. Transport mechanisms classified into : 1. Passive Transport > Simple diffusion > Facilitated diffusion > Osmosis > Bulk flow > Filtration

9. 2. Active Transport 3. Ion Channels > Ligand Gated Channels > Voltage Gated Channels 4. Vascular Transport > Exocytosis > Endocytosis 5. Uniport , Symport and Antiport

10. Transport Mechanisms Passive Transport a. Simple diffusion b. Facilitate diffusion c. Osmosis d. Bulk flow e. Filtration Active Transport Ion Channels Ligand Gated Voltage Gated Vascular Transport Exocytosis b. Endocytosis Uniport Symport & Antiport

11. Passive Transport : A. Simple Diffusion Solute and gases enter into the cells passively. They are driven by the concentration gradient. Simple diffusion occurs from higher to lower concentration. The rate of entry is proportional to the solubility of that solute. This does not require any energy , but it is a very slow process.

12. B. Facilitated Diffusion : It is a carrier mediated process Structurally similar solutes can competitively inhibit the entry of the solute. This mechanism does not require energy , but the rate of transport is more rapid than diffusion process. It is dependent on concentration gradient. Hormones regulate the number of carrier molecule. Examples of facilitated transport of glucose across membrane is by glucose transporters .

13. C. Osmosis : Osmosis is the process of moving water across a semi permeable membrane towards ion or solute rich region in a solution. Lower concentration to higher concentration through semi permeable membrane.

14. Ion Channels : Membranes have special devices called ion channels for quick transport of electrolyte such as Ca++, K+, Na+ and Cl - . These are selective ion conductive pores. Ion channels are specialized protein molecules that span the membrane. Cation conductive channels generally remains closed but in response to stimulus , they open allowing rapid flux ion down the gradient. This may compared to opening of the gate of a cinema house, when people rush to enter. Hence this regulation is named as “Gated”.

15. Based on the nature of stimuli that trigger the opening of the gate they are classified into :- 1 . Ligand Gated Channels : Acetylcholine receptor is an example for ligand gated ion channel. 2 . Voltage Gated channels : The channel is usually closed in the ground state. The membrane potential change switches the ion channel to open. Voltage gated Sodium channels and voltage gated potassium channels are the common examples

16. Active Transport : A. The salient features of active transport are :- This form of transport requires energy . About 40% of total expenditure in a cell is used for the active transport system. It requires specialized integral protein called transporters. The transporters are susceptible to inhibition by specific organic or inorganic compounds. B. Cell has low intracellular sodium; but concentration of potassium inside the cell is very high This is maintained by the sodium- potassium activated ATPase , generally called Sodium pump The ATPase as an integral protein of the membrane.

17. The hydrolysis of one molecule of ATP can result in expulsion of 3 Na+ ions and influx of 2K+ ion . The ion transport and ATP hydrolysis are tightly coupled.

18. Vesicular Transport : It is the transport of membrane bounded bounded substances moving across plasma membrane classified to :- 1. Endocytosis 2. Exocytosis Endocytosis: It is a process by which the large number of particles are taken with forming the vesicle into the cell. It is classified into :- 1. Phagocytosis It is a process by which the large number of particles are engulfed in to the cell.

19. 2. Pinocytosis It is a process by which the large number of particles which are soluble in water are taken into the cell.

20. Exocytosis Exocytosis is a process in which an intracellular vesicles (membrane bounded sphere) moves to the plasma membrane and fused the substance into the Extra cellular fluids.

21. Uniport , symport and Antiport : Uniport System Movement of a single substance It requires no energy from the cell Eg : Simple diffusion Facilitated diffusion Symport System Transport of two substances using the energy produced by concentration difference developed by primary active transport. Substances are moving in the same direction. Eg : Transport of amino acid , glucose transport

22. Antiport System In this process , the two substances move across the membrane in opposite directions . Eg : Sodium pump or chloride bicarbonate exchange in RBC

23. Recapitulation What is cell ? What is structure of cell membrane ? What are the functions of cell membrane ? What are the type of transport mechanisms ? Assignment What is cell organelles and briefly explain the cell organelles ?

24. Bibliography Vasudevan D M , S Sreekumari , Kannan vaidyanathan , Textbook of Biochemistry for Dental students , 2 nd edition 2011, Jaypee brothers medical publishers (P)Ltd, Page No: 1-6. Nicholas sperelakis , Cell Physiology source book , 3 rd edition, Academic press , Page No: 65-77.