Cell Membrane

Nota:

• most abundant lipids in membrane
• amphipathic (hydrophobic & hydrophillic regions)
• Functions: -form layers on surface of water -determine fluidity at lower temps (varying degrees of unsaturation in tails)

Nota:

• like phospholipids, but with sugars attached at head
• Found only on outside layer of plasma membrane
• Functions: -protect cell surface -act as recognition sites -help cells stick to surfaces

Nota:

• small, flat, ringed steroid between phospholipid molecules
• Functions: -decrease membrane fluidity -decrease membrane permeability -make membranes tougher

1. Enzymes
2. Transport
3. Receptors
4. Formation of Junctions
5. Cell-Cell Recognition
6. Attachment to extracellular matrix

1. Amphipathic
2. move around in membrane
3. some protrude on both sides of membrane

1. Simple Diffusion (high-low concentration)
   1. Non-polar solutes

      Nota:

      • cross easily (eg oxygen, hydrocarbons)
      • smaller molecules cross faster
   2. Polar solutes

      Nota:

      • small ones (eg Carbon Dioxide, Water) cross easily
      • larger molecules (eg sugars) won't pass readily
      • Ions pass hardly at all
2. Facilitated Diffusion (high-low concentration of solute)

   Nota:

   • polar solutes and ions are helped by transport proteins
   • solute is moving across a membrane from high-low concentration
   1. carrier proteins

      Nota:

      • bind to a solute and physically move them across membranes
      • very specific
   2. channel proteins

      Nota:

      • provide a hydrophilic channel for ions
      • less specific

Nota:

• molecules move against concentration gradient (low-high)
• Requires transport protein and energy input (eg Sodium / Potassium pump)

1. Eg) Sodium-Potassium pump

   Nota:

   • -found in plasma membrane
   • same carrier transports sodium and potassium ions across  membrane in opposite directions
   • 3 sodium ions out for every 2 potassium ions in
   • pump is "electrogenic" (produces a change in electrical charge) because it creates a membrane potential
   • uses ATP as energy
2. Molecules move against concentration gradient
3. requires transport proteins and energy

1. Ion pump works together with another protein transporter

   Nota:

   • Eg) glucose pump

Nota:

• can be PASSIVE or ACTIVE
• involves the movement of molecules through specialized channels

1. Voltage Gated Channels

   Nota:

   • -closed when electric potential is high (polarized) -open when potential is low (depolarized)
2. Ligand Gated Channels

   Nota:

   • -closed when concentration of molecule is low -open when concentration is high

1. Phagocytosis (uptake of solids)
2. Pinocytosis (uptake of fluids)
3. Receptor-mediated endocytosis (specific uptake of proteins)

1. reverse of endocytosis