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models of plasma membrane

This model failed to explain the thickness of the Membrane<br>Not all membranes are identical or symmetrical. <br>Membranes with different functions also differ in chemical composition and structure. <br>Membranes are bifacial with distinct inside and outside faces. <br>

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models of plasma membrane

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  1. MEMBRANE MODELS

  2. What do we mean by the term cell membrane?

  3. FUNCTIONS • Protects the cell • Semi permeable barrier • Maintain the concentration gradients • Allows cell recognition • Maintain shape of the cell

  4. MODELS OF PLASMA MEMBRANE • Gorter and Grendel model. • Sandwich Model of Plasma Membrane. • Fluid Mosaic Model of Plasma Membrane.

  5. GORTER AND GRENDEL • Investigated the surface area of lipids. • They extracted the lipids from RBC of human and animals in acetone. • The lipids were spread on a water surface in Langmuir trough. • Measured the surface area of the extracted lipid. • Calculation: surface area occupied by the extracted lipid surface area of all RBC membrane.

  6. SINCE, THERE IS ENOUGH LIPID TO GO AROUND THE RBC TWICE.HENCE, THEY PROPOSED THE MEMBRANE AS LIPID BILAYER.

  7. ERRORS • Acetone does not quantitatively extract all the lipids • Their calculation of membrane surface area also less than actual figure

  8. SANDWICH MODEL • A phospholipid bilayer is sandwiched between two layers of protein. • Phospholipid is essential because the lipid layer is permeable to polar molecules

  9. ERRORS • This model failed to explain the thickness of the Membrane • Not all membranes are identical or symmetrical. • Membranes with different functions also differ in chemical composition and structure. • Membranes are bifacial with distinct inside and outside faces.

  10. FLUID MOSAIC MODEL

  11. Fluid Quality Of Membranes • It was proposed by Singer and Nicholson. • Membranes are held together by hydrophobic interactions. • Most membrane lipids and some proteins can drift laterally within the molecules. • Molecules rarely flip transversely across the membrane. • Some membrane proteins are tethered to cytoskeleton and cannot move far. • Membrane must be fluid to work.

  12. Membranes As Mosaics Of Structure n Function • A membrane is a mosaic of different proteins embedded and dispersed in the phospholipid bilayer. They vary in both structure n function. Two types • Integral proteins • Peripheral proteins

  13. INTEGRAL PROTEINS • Unilateral, reaching only a part way across the membrane. • strongly associated with bilayer • strong, hydrophobic (van de Waals’) forces

  14. PERIPHERAL PROTEINS • Not embedded but attached to membranes surface. • On cytoplasmic side, may be held by filaments of cytoskeleton.

  15. Cholesterol : A “fluidity buffer • Cholesterol molecule are embedded in animal cell membrane not in plant cell membrane they make the membrane ( along with phospholipids) impermeable to water soluble substance. it also stables the membrane. • Below Tm - cholesterol disrupts close packing of acyl chains  increases fluidity • Above Tm - cholesterol constrains motion of acyl chains  decreases fluidity

  16. Membranes are asymmetric. • The two layers may differ in lipid composition, proteins in the membrane have a clear direction. • The outer surface also has carbohydrates. • This asymmetrical orientation begins during synthesis of new membrane in the endoplasmic reticulum.

  17. CONCLUSION • It provides a barrier between the inside and outside environment of the cell, and plays an important role in cell to cell signaling and communication. • It is composed primarily of phospholipids and proteins, and the exact composition of the cell membrane varies depending on the cell type. •  Although there is a wide variety of cell types which exist in nature, one uniting feature they share is the cell membrane.

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