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Cell Membrane & it-s Functions.pdf

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Cell Membrane & it-s Functions.pdf

  1. 1.  The cell and its organelles are surrounded by Membranes composed of Lipids & proteins.  Theses membranes include the cell membrane, nuclear membrane, membranes of ER, Mitochondria, lysosomes & golgi apparatus.
  2. 2. 1. Cell membrane provide barrier that prevent free movement of water and water-soluble substances from one cell compartment to another. 2. Proteins in the cell membrane provide the pathway to allow movement of specific substances through the membrane
  3. 3.  Cell membrane is a Lipid Bilayer with Inserted proteins.  The lipid bilayer is composed of Phospholipids and Cholesterol.  Phospholipids have two portions: 1. Hydrophilic portion= Water-soluble portion 2. Hydrophobic portion= Fat soluble portion
  4. 4.  Lipid bilayer is highly permeable to lipid soluble substances Such as O2,CO2,alcohol etc.  But it act as a barrier for water soluble substances Such as Ions & glucose  )
  5. 5.  Many protein are also floating in lipid bilayer. These proteins are Glycoproteins ( proteins combine with Carbohydrates)  There are 2 types of proteins: 1. Integral proteins 2. Peripheral protein
  6. 6.  These proteins protrude through the membrane.  Function: 1. They provide structural channels (pores)through which water soluble substances specially Ions can diffuse 2. They act as carrier proteins for the transport of substances, sometimes against the gradient for diffusion it is called Active transport. 3. They also serve as receptors for substances such as peptide hormones because they donot cross cell membrane easily (second messsenger)
  7. 7.  These proteins are attached to the inner surface of membrane but do not penetrate  Function : 1. They serve as function enzymes that catalyze chemical reactions of cells.
  8. 8.  These are in combination with proteins and lipids in form of glycoproteins and glycolipids.  Glyco portion usually protrude outside of the cell.  Proteoglycans = These are small carbohydrate molecules bound together by small protein cores, are loosely attached to the outer surface.  Glycocalx =It is a loose outer carbohydrate coat that surrounds the cell
  9. 9. 1. They are often negatively charged and therefore repel other molecules negatively charged. 2. The glycocalx of cells may attach to other cells 3. Some are act as receptors for binding hormones.

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