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CELL MEMBRANE

CELL MEMBRANE. DR.IMRANA EHSAN. Structure and function of cell components. Carbohydrates Lipids Proteins Nucleic Acids Membranes Cytoskeleton. The plasma membrane is the boundary that separates the living cell from its nonliving surroundings

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CELL MEMBRANE

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  1. CELL MEMBRANE DR.IMRANA EHSAN

  2. Structure and function of cell components Carbohydrates Lipids Proteins Nucleic Acids Membranes Cytoskeleton

  3. The plasma membrane is the boundary that separates the living cell from its nonliving surroundings • The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others

  4. Many organelles contain or are enclosed by membranes, including • Plasma membrane • Mitochondria • Chloroplasts • Nuclear envelope • Endoplasmic reticulum • Golgi apparatus • Lysosomes • Microbodies (aka perioxisomes) Cell membranes

  5. Phospholipids are the most abundant lipid in the plasma membrane • Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions • The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it. Cellular membranes are fluid mosaics of lipids and proteins

  6. Structure of cell membrane

  7. 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 Fluidity of Membranes

  8. As temperatures cool, membranes switch from a fluid state to a solid state • The temperature at which a membrane solidifies depends on the types of lipids • Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids • Membranes must be fluid to work properly; they are usually about as fluid as salad oil

  9. As temperatures cool, membranes switch from a fluid state to a solid state • The temperature at which a membrane solidifies depends on the types of lipids • Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids • Membranes must be fluid to work properly; they are usually about as fluid as salad oil

  10. Based on the functions of the above organelles / membranes write down some of the roles of the membranes in the cells • (Leave some space as we will be adding to this list) Role of Cell Membranes

  11. Structure of Cell membranes • Fluid Mosaic Model

  12. Electron micrograph of cell membrane

  13. Lipids • Remember lipids have hydrophilic head and hydrophobic tails • To avoid the hydrophobic tails coming in contact with water a continuous bilayer sphere is formed. • Therefore hydrophobic interactions hold membranes together Structure of Cell membranes

  14. Proteins • Integral proteins (intrinsic) • Proteins that are embedded in the membrane • They are held in place by hydrophobic interactions (integral proteins have hydrophobic groups on their outer surface) • Peripheral proteins (extrinsic) • Proteins attached to the surface of the membrane (often forming non-covalent bonds with integral proteins) Structure of Cell Membranes

  15. Proteins cont…

  16. Phospholipid bilayer • Forms boundary to isolate cell contents from environment • Restricts passage of hydrophilic substances across the membrane • Cholesterol • Increases bilayer strength, flexibility • Reduces membrane fluidity • Reduces permeability to water-soluble substances Function of membranes macromolecules

  17. Some proteins in the plasma membrane can drift within the bilayer • Proteins are much larger than lipids and move more slowly

  18. Attachment • Cytoskeleton • Extracellular matrix • Intercellular Junctions • Plasmodesmata • Tight Junctions • Gap Junctions • Desmosomes Function of Membrane Proteins

  19. Transport • Carrier Proteins • Channel Proteins • Receptors • Enzymes • Cell to Cell recognition Function of Membrane Proteins

  20. Integral • (Membrane-spanning or intrinsic) • •Can span membrane several times • •Either move around or are kept in place by cytoskeleton proteins Allows for cell polarity • Associated (peripheral or extrinsic) • •Loosely bound to membrane • •Enzymes and structural proteins Function of membrane protiens

  21. Use all resources to find out more about the functions of membrane proteins. • Based on the functions of proteins, add to your list on the role of membranes in cells Learning Activities

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