Week 1

• Solvent in cells are typically H20 (water)

• Solute in cells are typically:

  • Glucose

  • Amino acids

  • Ions - Sodium ions and potassium ions

  • Chloride

  • Calcium

Plasma membrane:

• Phospholipid bilayer = two layers

  • Security guard!! Tells what goes out and what goes in

• Differentially or selectively permeable (depends on what needs to come in or out of the cell)

• Most organelles of eukaryotic cells also have membranes (organelles inside our cells ALSO have membranes)

• Two components:

  • Hydrophilic head containing phosphate

  • Hydrophobic tail containing fatty acid side chains

• Phospholipid molecules:

  • Phosphate containing head group is hydrophilic (attracted to water)

  • Fatty acid tails are hydrophobic (repels water)

  • Phospholipid bilayer forms a hydrophobic barrier

    • Non polar substances can pass through easily while polar substances cannot (find difficult). Molecules that are too large ALSO cannot pass through

  • Important!! Differentiation polar molecules from non-polar

    • Polar molecules have uneven distribution of electrons (positive AND negative end --> dipole)

    • Non-polar molecules have an even distribution of electrons --> NO dipole

• Polar: Glucose, amino acids (a.a) e.g.

• Non polar: Ions e.g.

• Cell membrane is dynamic!! Can separate and rejoin to allow larger molecules to come in

• Diffusion continues until equilibrium is met (equal concentration)

• Simple diffusion

  • SMALL and UNCHARGED (non-polar) molecules, lipid soluble molecules or water DIRECTLY passing through the plasma membrane

  • From ALONG the concentration gradient (high --> low)

  • NO transport protein required

  • NO energy required (passive process)

• Facilitated diffusion

  • Specific ions (potassium, sodium ions e.g.)

  • FASTER than simple diffusion

  • SOME molecules from facilitated diffusion CAN also use simple diffusion, but just takes longer (more difficult)

  • Each channel/protein is SELECTIVE (only let in one TYPE of ion)

  • Channels become saturated as concentration of transport substance increases

  • Only transport molecules or ions DOWN a concentration gradient

• Osmosis: Refers to the movement of water form an area of LOW solute concentration to an area of HIGH solute concentration.

  • High H20 = Low solute (Vice versa)

  • Water molecules care about the concentration of SOLUTES on the other side (looking at amount, and volume)

  • Moves low solute concentration to higher solute concentration

  • Water molecules can move through aquaporins OR move directly through the phospholipid layer

    • Aquaporins = type of facilitated diffusion and is a type of transport protein

• Keep moving across until the equilibrium is reached!!!

• Hypotonic solution (important!!) = lower solute concentration/less

• Hypertonic solution = higher solute concentration/many

• Isotonic solution = same solute concentration