Cell Membrane

 

Role of cell membrane

Maintains homeostatis

Allows some things to pass through and others not to (selectively permeable)

The cell membrane is a bilipid layer with two sheets of phospholipids:
  1. Phosphate Group (Head):

   a. polar and water soluble

   b. attracts water by hydrogen bonds (hydrophilic)

    

  1. Fatty Acids (Tails):

   a. nonpolar and insoluble

   b. repels polar molecules, sugars, proteins, ions, cell wastes,…(hydrophobic)

    

   Eukaryotes have cholesterol: gives rigidity and strength, and separates the fatty acid tails

    

Proteins are also in the Membrane:
  1. Peripheral- on surface
  2. Integral- through the membrane

    

Functions of Cell Intergeral Proteins:

A. Transport Proteins: (channel and carrier) gates through the membrane that only fit specific particles

 

B. Receptor Proteins: Transmit information through the membrane

Receptor: fits specific signal molecules, triggering a response.

 

  1. Intracellular receptor: messenger molecule crosses membrane and binds to receptor inside cell to then enter nucleus and impact DNA (ex-steroids hormones)

    

  1. Membrane receptor: molecule binds on cell surface receptor which sends message into cell causing chain of events inside cell (ex – neurotransmitters)

    

C. Cell Surface Markers

identify cell to other cells by carbohydrate attached

 

D. Enzymes

 

E. Attach to cytoskeleton

 

Carbohydrates in Cell Membrane

Glycoproteins: Attached to proteins

Glycolipids: Attached to lipids (specifically phospholipids)

 

Fluid Mosaic Model- Current model of cell membrane

Fluid: Molecules can move sideways in the membrane

Mosaic: Cell membrane is composed of different types of molecules