1. Why is cholesterol an important feature of the cell membrane?
I’m Matthew
Do Now 10/29
Why is cholesterol an important feature of the cell membrane?

2. 10/27
Study on your own for a few minutes- quiz today on prokaryotic/eukaryotic cells AND organelles!

3. 10/30
You have a cell, with a semi permeable membrane and a 1.5% potassium concentration. You put it into a solution of 2% potassium. What adjective describes the solution? What direction would you expect water to flow? What do you expect to see happen to the cell?

4. Transport in/out of cells

5. Cell membrane: Made of Phospholipids
Phosphate
“attracted to water”
Phosphate head
Hydrophilic: attracted to water
Fatty acid tails
Hydrophobic: repelled by water
Arranged as a bilayer
Fatty acid
“repelled by water”

6. Cell membrane defines cell
Cell membrane separates living cell from environment
Controls traffic in & out of the cell
allows some substances to cross more easily than others
=semi-permeable

7. Cell membrane is more than lipids…
Proteins embedded in phospholipid bilayer
Create channels
protein channels in lipid bilyer membrane

8. Any Questions??

9. Movement across the Cell Membrane

10. Concentration of Solutions:
How much solute is dissolved in the solvent
Unit is usually in grams/liter
Sometimes reported in a percentage (%) or in Molarity (M)

11. Concentration Gradient
When one side of the cell has a much higher concentration than the other side of the cell
Equilibrium:
Solutes move to make both sides the same concentration

12. Types of Transport: 1. Simple Diffusion
Move from HIGH to LOW concentration
no energy needed

13. 2. Facilitated Diffusion
facilitated = with help
Diffusion through protein channels (HIGH to LOW concentration)
channels move specific molecules across cell membrane
no energy needed
Donuts!
Each transport protein is specific as to the substances that it will translocate (move).
For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer.
Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane.
These channel proteins allow fast transport.
For example, water channel proteins, aquaporins, facilitate massive amounts of diffusion.

14. 3. Active Transport
Cells may need to move molecules against concentration gradient (LOW to HIGH)
Proteins transports solute from one side of membrane to other
protein “pump”
Uses energy
Some transport proteins do not provide channels but appear to actually translocate the solute-binding site and solute across the membrane as the protein changes shape. These shape changes could be triggered by the binding and release of the transported molecule. This is model for active transport.

15. Transport summary simple diffusion facilitated diffusion
ATP
active transport

16. The Special Case of Water Movement of water across the cell membrane

17. 4. Osmosis: is just diffusion of water
Water is very important to life, so we talk about water separately
Diffusion of water from HIGH concentration of water to LOW concentration of water

18. Concentration of water
Direction of osmosis is determined by comparing total solute concentrations
Hypertonic - more solute, less water
Hypotonic - less solute, more water
Isotonic - equal solute, equal water
hypotonic
hypertonic
water
overall movement of water

19. Do you understand Osmosis…
Cell (compared to beaker)  hypertonic or hypotonic
Beaker (compared to cell)  hypertonic or hypotonic
Which way does the water flow?  in or out of cell

20. Any Questions??