Plasma membranes

Components
1. Glycocalyx
  1. Found on the cells surface, they are imbeddded in the membrane and have a carbohydrate chain extending outwards.
    1. Glycolipids: consist of a carbohydrate and a lipid. They are involved in the recognition of self/ non-self cells
    2. Glycoproteins: Consist of a carbohydrate and a protein. They are involved in cell to cell communication and transport through the membrane.
    3. They serve as protein binding sites and cell lubrication and adhesin molecules
2. Cholestrol molecule
  1. found within the cell molecule, acts as a patching substance which helps to regulate membrane and fluidity.
    1. Made of lipid component of cell membranes and acts to help stiffen the membrane. it si not found in plant cells
3. Proteins
  1. Can be structural/ integral (bound to hydrophobic interior of cell membrane) or periferal ( not bound this way)
    1. Structural proteins: Help to give cell support and shape
    2. Receptor proteins: Help cells to communicate with their external environment by using hormones, neurotransmitters adn other siganling molecules
    3. Tranport proteins: such as globular proteins accross cell membranes through facillitated diffusion.
4. Phospholipid bilayer
  1. A double layer of pholipid molecules whoose hydrophilic heads face outward and hydrophobic tails face inwards, towards eachother.
    1. Phospholipids: Are molecules composed of two fatty acid chains linked to a charged phosphae group.
      1. Fatty acid chains are hydrophobic and phosphate is hydrophilic. This means the fatty acids avoid water while the phosphate readily bonds with it.
        Hydrophobic molecules pass through freely while hydrophilic molecules do not pass through freely.
    2. Phospholipids take on thsi configuartion as protection from water, in cytosol.
Movement is driven by three things.
1. Energy
2. Differance in concentration.
3. Differance in concentration of substance unable to cross a membrane
Types of movement across a membrane.
1. Ozmosis
  1. The net movement of water molecules across a partially premiable membrane, hte movement is down the concentration gradient.
    1. Occurs when other particles cannot cross membrane and hense in used as a method to creat an equilibrium.
    2. Hyper, highly concentrated solutions
    3. Hypo, solutions with a low concentration
    4. Iso, solutions with the same concentration
  2. Solution types:
    1. Hypertonic solutions have more solute outsied cell causing water to diffuse across and allowingthe cell to shrink and die.
    2. Hypertonic solutions have less solute molecules outside the cell that inside and this causes water to diffuse into the cell adn hte cell will grow.
    3. Isotonic solutions have equal solute on both sides and because of thsi the water moves back and forth not changing the concentration.
2. Diffusion
  1. movement of molescules across the plasma membrane as a result of the concentration gradient. This does NOT require energy.
    1. Takes place through phospholipid bilayer.
  2. Facilitated diffusion: Occurs due to a protein channel or a carrer protein. when large water soluble molecules diffuse through protein channels.
3. Active trasnport
  1. moves disolved substance from a high to concentration to a low concentration. requires energy. Must take place through carrier proteins and pumps.
    1. Sodium potassium pump: the cell pumps out 3 sodium ions and takes in 2 potassium ions. Pumps and channels require energy.
4. Bulk trasnport
  1. Endocytosis: the bulk movement of solid particles into a cell. The membranes forms a vessicle around the particle and creates a vessicle.
  2. Exocytosis: bulk movement of particle out of a cell, they are enclosed in a vessicle which then fuses with plasma membrane an they are released, minus
Ions: Cannot diffuse through membrane as they are charged molecules and hense require proteins (channels or carriers)
1. Eg:- when sodium chloride enters water, it breakes for compund to the Na and Cl molecules.
  1. Water: Crosses phospholipid bilayer by osmosis.
2. Glucose: passes through the phospholipid bilayer by using a carrier protein
3. Ions: Cross phospholipid bilayer with th ehelp of special/ specific proten channels
DIfferant types of passive transport
1. Diffusion
2. Channel mediated: Molecules which cannot carry out simple diffusion pass theough protin channel
3. Carrier mediated:Protein molecule alone is insufficient and carrier molecule is needed to bring through protein chanel. facilitated diffusion= specifi

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Plasma membranes

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