FLUID MOSAIC MODEL OF THE CELL MEMBRANE

1. By: Mrs. Y Bharathi PGT Bio, KV Nalgonda Hyderabad Region FLUID MOSAIC MODEL OF THE CELL MEMBRANE

2. What is a cell membrane? The cell membrane surrounds the cytoplasm of a cell and, in animal cells, physically separates the intracellular components from the extracellular environment, thereby serving a function similar to that of skin. In fungi, some bacteria, and plants, an additional cell wall forms the outermost boundary; however, the cell wall plays mostly a mechanical support role rather than a role as a selective boundary

3. Cell membrane All living things are surrounded by a membrane. • Controls exchange of materials such as nutrients and waste between cells and their environment. • Has other important functions for example to enable cells to receive hormones. • To understand the function of anything in biology, you must study the structure first!

4. Fluid mosaic model is the most acceptable model to describe the structure. The model is proposed by S.Jonathan Singer and Garth Nicolson in 1972 STRUCTURE OF PLASMA MEMBRANE There are many models proposed to explain the structure of Plasma membrane

5. KEY WORDS • Fluid Mosaic • Phospholipid • Polar and non polar • Hydrophilic • Hydrophobic • Cholesterol • Intrinsic • Extrinsic • Proteins

7. Cell membranes are made of PHOSPHOLIPIDs • HYDROPHILIC heads (water liking)-Attracted to the water • called POLAR • HYDROPHOBIC tails (water fearing)-Not attracted to the water • called NON-POLAR

8. Phospholipids are important structural components of cell membranes. Phospholipids are modified so that a phosphate group (PO4-) replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a polar "head" and two non polar "tails".

9. A Phospholipid Bilayer Phospholipids can form: BILAYERS -2 layers of phospholipids with hydrophobic tails protected inside by the hydrophilic heads. The PHOSPHOLIPID BILAYER is the basic structure of membranes.

11. Two types of proteins a)Integral or intrinsic and b)Peripheral or extrinsic Peripheral proteins :are located superficially and do not cover always the entire surface of phospholipid matrix Loosely bound to the membrane surface . And they can be easily extracted. proteins

12. Integral proteins:70% of total membrane protein Embedded in the phosphobilipid layer They are tightly held in place .by strong hydrophilic or hydrophobic interactions or both. With the polar heads and nonpolar tails.

13. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix to help group cells together in the formation of tissues. • The barrier is selectively permeable and able to regulate what enters and exits the cell, thus facilitating the transport of materials needed for survival. • The movement of substances across the membrane can be either passive, occurring without the input of cellular energy, or active, requiring the cell to expend energy in moving it. The membrane also maintains the cell potential.

14. The arrangement of hydrophilic and hydrophobic heads of the lipid bilayer prevent polar solutes (e.g. amino acids, nucleic acids, carbohydrates, proteins, and ions) from diffusing across the membrane, but generally allows for the passive diffusion of hydrophobic molecules. This affords the cell the ability to control the movement of these substances via transmembrane protein complexes such as pores and gates.

15. Summary • Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER. • Phospholipds have HYDROPHOBIC (non-polar) tails and HYDROPHILIC (polar) heads. • The best model of the cell membrane is called the FLUID MOSAIC MODEL • The average thickness of the membrane is 7nm. • The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED (bent) • Proteins can float or be fixed and also have hydrophobic and hydrophilic portions. • Some proteins and phospholipids have carbohydrates attached to them to form GLYCOPROTEINS AND GLYCOLIPIDS. • Phospholipids form the bilayer, act as barrier to most water soluble substances • Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane. • Proteins act as transport proteins to act as channels for substances to move into or out of the cell. Some act as membrane enzymes and some have important roles in membranes of organelles. • Glycolipids and Glycoproteins help to stabilise membrane structure, some act as receptor molecules eg for hormones and neurotransmitters or as antigens for other cells to recognise them.

17. Thank you