1. The Cell Membrane

2. Warm Up 1/31/17
What would happen if you gave a patient an IV of pure water?
a. Their blood cells would shrink.
b. Their blood cells would burst.
c. The patient would slowly become rehydrated.
d. I would be promoted for my outstanding level of medical care.

3. For a free 100… Text this number: 81010
With this code as the

4. What you need to know…
You need to predict how molecules move across membranes
You need to know the difference between active and passive transport

5. Overview Cell membrane separates living cell from surroundings
Controls traffic in & out of the cell
selectively permeable
hydrophobic vs hydrophilic
Made of phospholipids, proteins & other macromolecules

6. Aaaah, one of those structure–function
Phospholipids
Phosphate
Fatty acid tails
hydrophobic
Phosphate group head
hydrophilic
Arranged as a bilayer
Fatty acid
Aaaah, one of those structure–function
examples

7. Movement across the Cell Membrane

8. Diffusion Diffusion movement from high  low concentration
Movement from high concentration of that substance to low concentration of that substance.

9. Diffusion Move from HIGH to LOW concentration movement of water
“passive transport”
no energy needed
movement of water
diffusion
osmosis

10. Diffusion through phospholipid bilayer
What molecules can get through directly?
fats & other lipids
What molecules can NOT get through directly?
polar molecules
H2O
ions
salts, ammonia
large molecules
starches, proteins
lipid
inside cell
outside cell
salt
NH3
sugar aa
H2O

11. Channels through cell membrane
Membrane becomes semi-permeable with protein channels
specific channels = specific materials
inside cell
H2O aa
sugar
salt
outside cell
NH3

12. Facilitated Diffusion
Diffusion through protein channels
channels move specific molecules across cell membrane
no energy needed
facilitated = with help
open channel = fast transport
low
high
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.
“The Bouncer”

13. conformational change
Active Transport
Cells may need to move molecules from low to high concentration
protein “pump” used
“costs” energy (ATP)
conformational change
low
high
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.
ATP
“The Doorman”

14. Active transport Many models & mechanisms ATP ATP antiport symport
Plants: nitrate & phosphate pumps in roots.
Why?
Nitrate for amino acids
Phosphate for DNA & membranes
Not coincidentally these are the main constituents of fertilizer
Supplying these nutrients to plants
Replenishing the soil since plants are depleting it
antiport
symport

15. Getting through cell membrane
Passive Transport
Simple diffusion
diffusion of nonpolar, hydrophobic molecules
lipids
high  low concentration gradient
Facilitated transport
through a protein channel
Active transport
diffusion against concentration gradient
low  high
uses a protein pump
requires ATP
ATP

16. Transport summary simple diffusion facilitated diffusion
ATP
active transport

17. How about large molecules?
Moving large molecules into & out of cell
through vesicles & vacuoles
endocytosis
phagocytosis = “cellular eating”
pinocytosis = “cellular drinking”
exocytosis
exocytosis

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

19. Osmosis is diffusion of water
Diffusion of water from high concentration of water to low concentration of water
Across membrane

20. 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
net movement of water

21. Managing water balance
Cell survival depends on balancing water uptake & loss
freshwater
balanced
saltwater

22. Water regulation
Contractile vacuole in Paramecium
ATP

23. Osmosis…
.05 M
.03 M
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

24. Exit Ticket: Justify Why!
An animal cell is placed in a saltwater solution. Predict what might happen to the cell when exposed to this solution.
Describe the solution too. Is it hypertonic, hypotonic, or isotonic?

25. Any Questions??