4

• Cell membrane


  Every cell is surrounded by the cytoplasmic membrane, which separates intracellular from extracellular space. Its average thickness is 7.5-10 nm.

  
• Cell membrane


  Selectively permeable boundary, which ensures the maintenance of dynamic equilibrium between cell and environment (Allows some molecules in and keeps other molecules out)

  
• Other names for cell membrane


  • Cell Membrane
  • Phospholipid Bilayer
  • Lipid Bilayer
  • Plasma Membrane
  • Fluid Mosaic Model

  
• Cell membrane


  • Selectively Permeable
  • Regulates what enters/exits cell
  • Helps transport certain molecules across with help of proteins
  • Bilayer
  • Hydrophobic
  • Hydrophilic
  • Embedded proteins (different functions)

  
• Fluid-mosaic model


  • Fluid = pliable/easily moved
  • Mosaic = made of many different molecules (lipids, proteins, carbohydrates)

  
• Components of cell membrane


  • Lipids (present as lipid bilayer)
  • Proteins (surface proteins, transmembrane proteins)
  • Carbohydrates (attached with proteins they form the receptors and other structures)

  
• Phospholipids


  Composed of polar (hydrophilic) head and two non-polar (hydrophobic) fatty acids chains. In the aqueous environment the hydrophilic parts are oriented towards the water around them and fatty acids chains to each other, creating so-called phospholipid bilayer.

  
• Membrane proteins


  • Integral (determine a membrane's specific functions, which affect the hydrophobic parts of the phospholipid bilayer or transgress it)
  • Peripheral (lie outside the lipid bilayer, play a structural role by helping to stabilize and shape the plasma membrane)

  
• Functions of membrane proteins


  • Structural proteins
  • Transport of ions across the membrane (pump and ion channels)
  • Transfer of substances along the electrochemical gradient by facilitated diffusion
  • Channel protein
  • Carrier protein
  • Cell recognition protein
  • Receptor protein
  • Enzymatic protein

  
• Cystic fibrosis is caused by faulty chloride (Cl-) channel
• The inability of some person to use energy to sodium – potassium (Na+ , K+ ) transport has been suggested as the caused of their obesity
• Pygmies are shorts not because they do not produce enough growth hormone, but because their plasma membrane growth hormone receptors are faulty and cannot interact with the growth hormone
• The carbohydrate chains of Glycolipids and glycoprotein serve as the finger prints of the cell
• Functions of cell membrane


  • Transportation: Regulating the movement of substances into and out of the cell
  • Providing structural support for the cell
  • Acting as a barrier to protect the cell from its environment
  • Detecting changes in the environment and sending signals to the rest of the cell in response to these changes
  • Maintaining the cell's shape
  • Producing energy for the cell
  • Helping to repair damaged cells
  • Identification
  • Communication
  • Defense
  • Prevents the cell from Dehydration
  • Provides protection and support for the cell
  • Allows mobility in some organisms
• Intercellular junctions


  • Zonula occludens (close connection, at which the cell membranes of neighbouring cells make contacts)
  • Zonula adhaerens (arises as a continuation of the zonula occludens towards to basal part of cells)
  • Macula adhaerens (desmosome) (strongest and most complex cell connection in shape of disk which arises at the base of cells)

  
• Membrane receptors


  • Receptors which are part of the ion channels
  • Receptors with enzyme activity
  • Receptors coupled to G proteins