Membrane Transport

Membrane Transport • Passive Transport • Moves from high to low concentration • Does not require energy

3) Diffusion • Movement of small & polar/nonpolar particles across bilayer. • Bilayer is permeable to the particle O2 CO2 Glycerol No transport proteins are required

Rates of Diffusion depends on Concentration difference Temperature Pressure

RATES OF DIFFUSION DEPEND ON... • concentration of the diffusing molecule • The greater the difference in concentration between two areas, the greater the rate of diffusion ∴ direct relationship • temperature • The greater the temperature, the greater the rate of diffusion because temperature increases the rate of molecular movement ∴ direct relationship • pressure • The greater the pressure, the greater the rate of diffusion because pressure increases the rate of molecular movement ∴ direct relationship

Example: Diffusion of CO2 and O2 into and out of lung alveoli Watch this 1:34 minute video Add red dots to illustrated the movement of oxygen gas. Add blue dots to illustrated the movement of carbon dioxide gas. Be sure to correctly show movement from areas of higher to lower concentration!

Example: Diffusion of CO2 and O2 into and out of eye cornea cells The cornea is the transparent front part of the eye that covers the iris and pupil. Because the cornea must be transparent (so light can pass through), the cornea does not have blood vessels. But, the cells of the cornea are alive and must receive oxygen and get rid of carbon dioxide waste. How can this happen? You guessed it… the cornea receives nutrients via diffusion from the tear fluid through the outside surface and the vitreous humour (eyeball juice) through the inside surface. Think about the implications for people who wear contact lenses… If you can handle it, watch this video of a cornea transplant

4) Osmosis • Movement of water from low solute to high solute concentrations across a membrane Solutions: Hypertonic – high solute concentration Hypotonic – low solute concentration Isotonic – equal (equilibrium) H2O

HYPOTONIC The cell has a higher solute concentration than the solution. So, the solution is HYPOTONIC and the cell is hypertonic. Since water moves from hypotonic to hypertonic solutions NET water movement will be into the cell and the cell will swell. If too much water moves into the cell, it will burst.

ISOTONIC The cell has the same solute concentration as the solution. So, the cell and the solution areISOTONIC. There will be no NET water movement and the cell will remain the same size.

HYPERTONIC The cell has a lower solute concentration than the solution. So, the solution is HYPERTONIC and the cell is hypotonic. Since water moves from hypotonic to hypertonic solutions NET water movement will be out of the cell and the cell will shrink. If too much water leaves the cell, it will die.

Be prepared to explain one of the following: • Why organs must be stored in an isotonic solution when being transported for transplant surgery. • Why IV lines given at hospitals must be an isotonic solution to the blood. • Why a person needs to use a contact lens solution and not just water when storing and cleaning contact lenses. • Why salt put on roads during winter storms will kill the plants along the roadway. • Why salting a slug is probably the most unethical way for a slug to die. • Why your fingers will prune (swell) after a bath or swim.

5) Facilitated Diffusion • Movement of large/charged particles through proteins Glucose, Amino Acids, H+ * Diameter and chemical properties of proteins are particle specific

PHOSPHOLIPID BILAYER MUST BE... studded with channel proteins to allow facilitated diffusion to occur. Channels are holes through a protein with very narrow diameter. The diameter and chemical properties of the proteins ensure that only one type of particle can pass through. For example, sodium ions or potassium ions, but not both. Example channel created by a hole surrounded by protein

EXAMPLE The CFTR Channel moves chloride ions out of the cell. People with cystic fibrosis have a mutation that causes the CFTR channel to have the wrong shape and as a result the channel can not move the chloride ions. The ions build up in the cell. The consequences are huge.

Brain Break

2) Active Transport • Movement of particles against concentration gradient (CG) • Requires energy

6) Molecular Active Transport • Uses ATP for energy to transport substances against CG with transport protein.

8) Primary Active Transport • Moves from low to high concentration • protein pump phosphorylated by ATP Energy from ATP changes protein shape to allow molecule to pass through Na-K Pump

9) Secondary Active Transport • Moves from low to high concentration • Energy comes from primary active transport. Moves in 1 direction Moves in opposite directions

EXAMPLE: Sodium Potassium Pump in Neurons This graphic illustrates one sodium-potassium pump over time. On your notes, annotate with: • direction of sodium transport (into or out of cell) • direction of potassium transport (into or out of cell) • is sodium moving with or against its concentration gradient? • is potassium moving with or against its concentration gradient? Why does this pump matter? Long story short… without it you’d be dead.Here’s why.

EXAMPLE: Proton Pump in Cellular Respiration and Photosynthesis In order for cells to perform photosynthesis and/or respiration, protons (also known as H+ ions) must be pumped across the inner membranes of the mitochondria or chloroplast. Bonus review opportunity! Can you remember why mitochondria and chloroplasts have both an inner and outer membrane?

7) Bulk Transport • Movement of large quantities of substances with vesicles

10) Exocytosis Removing intracellular contents by fusion of vesicles with cell membrane

11) Endocytosis Engulfing extracellular contents with cell membrane creating vesicles around the particles

14) Receptor Mediated Endocytosis Cell engulfs target substances (ligands) from extracellular environment • Nutrients Ligand

12) Phagocytosis • Engulfs large solid content • “Cell eating” Bacteria Pseudopodium Phagosome (if food particle) White blood cell

13) Pinocytosis • Engulfs liquid environment • “Cell drinking” • Nutrients

Membrane Transport