CELL- STRUCTURE AND FUNCTIONS.pptx......

CELL- STRUCTURE AND FUNCTIONS.pptx......

1. CELL - STRUCTURE & FUNCTIONS PY. 1.1 DR. ASHA S DAS, PG RESIDENT, DEPT. OF PHYSIOLOGY, KoIMS, MADIKERI

2. PREVIOUSLY ASKED QUESTIONS (RGUHS) Give the structure and functions of cell membrane. Name the cell organelles and give their functions. Give the structure and functions of nucleus. Name various cytoskeletal elements and molecular motors of cell and give their functions. Classify intercellular junctions and give their functions. Describe the importance of gap junctions in health and disease. Give the structure, functions, of cell adhesion molecules, and microfilaments

3. INDEX CELL STRUCTURE & FUNCTIONS 1. Cell membrane * Fluid Mosaic Model *Arrangement of different molecules in cell membrane 2. Cytoplasm 3. Nucleus INTERCELLULAR JUNCTIONS • Tight junction • Adherens junction • Gap junction

4. The cell is the smallest structural and functional unit capable of carrying out life processes. The functional activities of each cell depend on the specific structural properties of the cell. The human body contains approximately 100 trillion cells . Under normal conditions, cells are dynamic structures existing in fluid environment ORGANIZATION AND FUNCTIONS OF CELL

5. Under a light microscope, a typical cell consists of three basic components: Cell membrane Cytoplasm Nucleus

6. Under a light microscope, a typical cell consists of three basic components: Cell membrane Cytoplasm Nucleus

7. The cell membrane is the protective sheath of the cell. It exchanges materials between the cytoplasm and the external environment. It facilitates interaction between cells and helps in anchoring the cells to each other. Cell Membrane

8. Structure of Cell Membrane Basically, a double layer of phospholipid molecules. Thickness of 7–10 nm, into which are inserted or attached various protein molecules. Lipids constitute about 42% of the dry weight of the membrane. Protein - 55% , and Carbohydrate - 3% . Fluid-Mosaic Model described by Singer and Nicolson in 1972.

9. FLUID-MOSAIC MODEL OF THE MEMBRANE It explains how membrane lipids exist in a flexible , fluid state , allowing the membrane to maintain its structural integrity . The membrane proteins are loosely attached and float in the fluid phospholipid bilayer. Rapid and random redistribution of integral proteins occurs in the membrane. Also, phospholipids undergo rapid redistribution in the plane of the membrane. This type of diffusion within the plane of the membrane is called translational diffusion. This occurs rapidly for phospholipids, which can move several micrometers per second.

10. Factors Contributing to Fluidity of Membrane 1. Temperature 2. Lipid composition of the membrane 3. Role of cholesterol Effect of temperature: In a lipid bilayer, the hydrophobic chains of fatty acids are highly aligned or arranged orderly to provide a stiff structure. When temperature increases , the hydrophobic side chains undergo a transition from its ordered gel or crystalline state to a more disordered liquid state .

11. Lipid Composition of Membrane: Fluidity is largely dependent on lipid composition. With rise in temperature , the unsaturated bond among fatty acid side chains lose their orderly, stiff arrangement .

12. Role of Cholesterol: Though cholesterol profoundly influences membrane fluidity, it behaves differently at different temperatures. It is rather a bulky molecule placed among the phospholipid bilayer.

13. * Determinant of the fluidity of the membrane * The fluidity of a membrane depends on the cholesterol-phospholipid ratio . In eukaryotes, the ratio is about 1:1 . Higher cholesterol content reduces the fluidity of the membrane.

14. Arrangement of different molecules in cell membrane

15. LIPID BILAYER The major lipids in the cell membrane are Phospholipids Glycolipids Cholesterol.

16. 1. Phospholipids The phospholipids are phosphatidylcholine, sphingomyelin, phosphatidylserine, and phosphatidyl ethanolamine.

17. 2. Glycolipids Glycolipids are generally found in the outer layer.

18. 3. Cholesterol Cholesterol is incorporated into the hydrophobic regions of the membrane and serves to reinforce the lipid permeability barrier.

19. Lipids are amphipathic molecules as their head or polar region is hydrophilic and tail or nonpolar region is hydrophobic. The globular or the head end contains phosphate or hydroxyl moieties that are soluble in water. The tail end contains two chains of fatty acids that are insoluble in water. The hydrophobic tail ends are directed toward the center and the hydrophilic head is located to periphery of the membrane . Thus, hydrophilic head of lipid molecules faces the aqueous phase from both inside and outside the cell.

20. Functions of the Lipid Bilayer To create a permeability barrier between the interstitial fluid and the cytoplasm. The permeability of a substance depends on whether it is lipid-soluble or water-soluble. • Lipid-soluble substances like oxygen and alcohol can pass easily through the cell membrane. • Water-soluble substances like urea and glucose cannot pass easily. Thus, lipid bilayer makes the membrane semipermeable.

21. MEMBRANE PROTEINS Membrane proteins are of two types : Integral Proteins Peripheral Proteins

22. 1. Integral Proteins: Some membrane proteins that span the entire thickness of the membrane are known as integral proteins. They are also called transmembrane proteins. The functions of integral membrane proteins are as follows: Serve as channel proteins Act as carriers Serve as ion pumps Serve as receptor and enzyme proteins Antigenic functions

23. 2. Peripheral Proteins: Some protein molecules are inserted lightly in the outer or inner border of the membrane or are just bound to the surface of the membrane. Such proteins are called peripheral proteins. a. Intrinsic proteins : They are present on the inner surface of the membrane. They usually serve as enzymes or anchor proteins for cytoskeleton and other microfilaments that maintain cell shape. b. Extrinsic proteins : They are present on the outer surface of the membrane. They serve as cell adhesion molecules (CAMs) for anchoring cells with basal lamina and with neighbouring cells. They can be removed without disrupting the membrane.

24. MEMBRANE CARBOHYDRATES The external surface of the cell membrane is loosely covered by a carbohydrate layer known as the cell coat or glycocalyx . Functions of the Glycocalyx: 1. Glycocalyx serves as a protective coat . Carbohydrate is negatively charged and therefore prevents negative particles like protein molecules to interact between cells. Some of the transmembrane glycoproteins like selectins , permit temporary cell-to-cell adhesion . Such temporary adhesion occurs between neutrophils and endothelial cells at the site of inflammation. Stronger adhesion between cells is formed by integral membrane proteins such as integrins . 3. Some carbohydrate molecules serve as receptors.

25. Functions of Cell Membrane 1. Cell membrane maintains a constant and distinctive intracellular environment , which is essential for functioning of the organelles. For example, the intracellular fluid has lower concentration of sodium and chloride, low pH, but higher concentration of potassium, organic phosphates, and magnesium. 2. Cell membrane maintains cell volume by actively transferring ions across it, especially by pumping sodium ions out of the cell. 3. In neurons and muscle cells, it maintains a potential difference between intracellular and extracellular surfaces, which enables cells to respond to various stimuli. 4. Cell membrane helps in recognising foreign cells or antigens so that they can be destroyed by phagocytes.

26. Special Features of RBC Membrane Integral Proteins Glycophorins: Glycophorins are glycoproteins that contain 60% carbohydrate and 40% protein. Band-3 proteins : It acts as “pore” or transport protein that exchanges bicarbonate ions in the capillaries of lungs.

27. 2. Peripheral Proteins The inner surface of red cell membrane contains two special proteins that are linked to the cytoskeleton and are essential for stabilization of membrane and biconcave shape of the cell. Spectrin : Along with ankyrin, it is attached to cytoskeletal protein that maintains membrane integrity and cell shape. Ankyrin: The cytoskeletal proteins are attached to spectrin through ankyrin. Ankyrin has two domains: one bind with spectrin and other with N-terminal region of band-3 protein that extends into cytoskeleton

28. APPLIED PHYSIOLOGY Diseases due to membrane protein defects: Disorders of red cells such as hereditary spherocytosis and elliptocytosis , occur due to defects in the membrane proteins

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