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Lecture 03

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The Cell Membrane

3. A film of extreme delicacy, of ultra microscopic thinness,
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What is cell membrane ?
A film of extreme delicacy,
of ultra microscopic thinness,
that forms a limiting layer on the surface of the cytoplasm.
and it is also called the plasma membrane (cell membrane).

4. Some properties of cell membrane
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Some properties of cell membrane
Cell membrane is living, elastic and made of proteins and lipids (fats).
The semipermeable nature of the plasma membrane is of the
greatest physiological significance in the functions of the
cell.

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The plasma membrane serves as the interface between the machinery in the interior of the cell and the extra cellular fluid (ECF) that bathes all cells.
It provides a mechanical barrier for the protection of the inner cell contents and to regulate the movement of molecules in and out of the cell.

6. Structure of cell membrane
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Structure of cell membrane

7. Gorter & Grendel’s membrane theory- (1925)
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Gorter & Grendel’s membrane theory- (1925)
Davson & Danielli model- ( )
Singer & Nicolson’s fluid mosaic model- (1972)
Henderson and Unwin’s membrane theory- (1975)

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The fluid mosaic model was first proposed by S.J. Singer and Garth L. Nicolson in 1972 to explain the structure of the plasma membrane.

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Hydrophobic
Lacking an affinity for water; unable to absorb, or be wetted by water, "water-fearing.“
Hydrophilic
Having an affinity for water; able to absorb, or be wetted by water, "water-loving.“
Amphiphilic
Having one surface consisting of hydrophilic amino acids and the opposite surface consisting of hydrophobic (or lipophilic) ones.

10. Figure: The Fluid Mosaic Model
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Figure: The Fluid Mosaic Model

11. The main fabric of the membrane is composed of amphiphilic or dual-loving, bilayer, phospholipid molecules. The lipids in the plasma membrane are chiefly phospholipids (like phosphatidyl ethanolamine) and cholesterol.
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13. Why lipid bilayer ??
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As the plasma membrane faces watery solutions on both sides, its phospholipids accommodate this by forming a phospholipid bilayer with the hydrophobic tails facing each other.

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Integral proteins, the second major component of plasma membranes, are integrated completely into the membrane structure with their hydrophobic membrane-spanning regions interacting with the hydrophobic region of the phospholipid bilayer. Peripheral proteins are also found here.

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Carbohydrates, the third major component of plasma membranes, are always found on the exterior surface of cells where they are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids).

16. Why it is called fluid mosaic model ??
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Figure: The Fluid Mosaic Model
Why it is called fluid mosaic model ??

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Functions
Acts as a boundary layer to contain the cytoplasm (fluid in cell).
Interlocking surfaces bind cells together.
Selectively permeable to select chemicals that pass in and out of the cells.

20. “Future is created by what you do today, not tomorrow.”
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“Future is created by what you do today, not tomorrow.”
Thank you