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Plasma Membrane

THE FLUID MOSAIC MODEL. Plasma Membrane. What is it? What is it made of? What is its function?. Structure of the Cell Membrane. Outside of cell. Carbohydrate chains. Proteins. Lipid Bilayer. Transport Protein. Phospholipids. Inside of cell (cytoplasm ). Animations

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Plasma Membrane

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  1. THE FLUID MOSAIC MODEL Plasma Membrane What is it? What is it made of? What is its function?

  2. Structure of the Cell Membrane Outside of cell Carbohydrate chains Proteins Lipid Bilayer Transport Protein Phospholipids Insideof cell (cytoplasm) Animations of membrane structure Go to Section:

  3. Fluid Mosaic Model of the cell membrane Polar heads love water & dissolve. Membrane movement animation Non-polar tails hide from water. Carbohydrate cell markers Proteins

  4. HOW DOES THE MEMBRANE MOVE? • A membrane is held in together by weak hydrophobic interactions. • Most membrane lipids and some proteins can drift laterally within the membrane • Molecules rarely flip transversely(flip-flop) across the membrane, because hydrophilic parts would have to cross the membrane’s hydrophobic core. Fig. 8.4a

  5. About Cell Membranes • All cells have a cell membrane • Functions: • Controls what enters and exits the cell to maintain an internal balance called homeostasis • Provides protection and support for the cell TEM picture of a real cell membrane.

  6. About Cell Membranes (continued) • Structure of cell membrane Lipid Bilayer-2 layers of phospholipids • Phosphate head is polar(water loving) • Fatty acid tails non-polar(water fearing) • Proteins embedded in membrane Phospholipid Lipid Bilayer

  7. About Cell Membranes (continued) • 4. Cell membranes have pores (holes) in it • Selectively permeable: Allows some molecules in and keeps other molecules out • The structure helps it be selective! Pores

  8. Membranes are mosaics of structure and function • A membrane is a mosaic of different proteins embedded and dispersed in the phospholipid bilayer. These proteins vary in both structure and function, and they occur in two spatial arrangements: 1- Integral proteins 2- Peripheral proteins

  9. TYPE OF INTEGRAL PROTEINS:in the plasma membrane may provide a variety of.

  10. FUNCTIONS OF INTEGRAL PROTEINS: Channel Protein: Allow a substance to move across the membrane (EX all hydrogen ions to flow across membrane of electron transport chain) Carrier Protein: Selectively interacts with specific molecules or ions so it can cross membrane (EX Sodium and Potassium pump) Cell Recognition Protein: Called “glycoproteins”, allow cell to be recognized by body’s immune system Receptor Protein: Specifically shaped to a specific molecule (EX liver stores glucose after insulin binds to cell receptor) Enzymatic Protein: Catalyze specific reactions (EX ATP metabolism)

  11. FUNCTIONS OF PERIPHERAL PROTEINS: To provide structural stability and shape to the plasma membrane

  12. What else can we find in this membrane? Cholesterol: helps control membrane fluidity by making the membrane: • Less fluid at warm temperatures (e.g. 37 C body temperature) by restraining the phospholipid movement. • More fluid at lower (cool) temperatures by preventing close packing of phospholipids. • Cells may alter membrane lipid concentration in response to changes in temperature Fig. 8.4c • Many cold tolerant plants (e.g. winter wheat) increase the unsaturated phospholipid concentration in autumn, which prevents the plasma membranes from solidifying in winter.

  13. Lastly, why is fluidity important?? • Membrane must be fluid to work properly. Solidification may result in permeability changes and enzyme deactivation. • Unsaturated hydrocarbon tails enhance membrane fluidity because kinks at the carbon-to-carbon double bonds hinder close packing of phospholipids.

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