1. CH 5:The Cell Membrane Movement and Mechanics

2. Ch 5A: Cell membrane Separates cell from its environment
Controls movement in & out of the cell
Selectively permeable
Made of phospholipids, proteins & other macromolecules
Lipid bilayer

3. Phospholipid bilayer polar nonpolar polar hydrophilic heads
hydrophobic
tails
polar
hydrophilic
heads

4. Why are proteins the perfect molecule to build structures in the cell membrane?

5. Fluid Mosaic Model

6. Proteins Within membrane On surfaces nonpolar amino acids
hydrophobic
anchors protein
On surfaces
polar amino acids
hydrophilic
Polar areas
of protein
Nonpolar areas of protein

7. Membrane is a collage of proteins & other molecules embedded in the lipid bilayer
Glycoprotein
Extracellular fluid
Glycolipid
Transmembrane
proteins
The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.
Phospholipids
Filaments of cytoskeleton
Cholesterol
Peripheral
protein
Cytoplasm

8. 5B:Movement across the Cell Membrane

9. Diffusion universe tends toward disorder (entropy)
2nd Law of Thermodynamics
universe tends toward disorder (entropy)
Movement from high concentration of that substance to low concentration of that substance.

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

11. Diffusion across cell membrane
OUT
waste
ammonia
salts
CO2
H2O
products IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
OUT IN
cell needs materials in & products or waste out

12. Facilitated Diffusion
Diffusion through protein channels
channels move specific molecules across
no energy needed
facilitated = with help
open channel = fast transport
high
low
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. specific channels allow specific material across cell membrane
inside cell
H2O aa
sugar
salt
outside cell
NH3

14. conformational change
Active Transport
Cells may need to move molecules against concentration gradient
Conformational shape change transports solute from one side to other
protein “pump”
“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

15. How about large molecules?
use vesicles & vacuoles
Endocytosis [in]
phagocytosis = “cellular eating”
pinocytosis = “cellular drinking”
Exocytosis [out]
exocytosis

16. The Special Case of Water

17. Managing water balance
Cell survival depends on balance
freshwater
balanced
saltwater

18. Isotonic Solution no net movement of water volume of cell is stable
flows across membrane equally, in both directions
volume of cell is stable
animal cell immersed in mild salt solution
example: blood cells in blood plasma
balanced

19. Hypotonic Solution a cell in fresh water example: Paramecium
problem: gains water, swells & can burst
water continually enters Paramecium cell
solution: contractile vacuole to pump (ATP) water out of cell
ATP
freshwater

20. Hypertonic Solution a cell in salt water plant cells
example: shellfish
problem: lose water & die
solution: take up water or pump out salt
plant cells
plasmolysis = wilt
saltwater

21. Osmosis is diffusion of water
high concentration of water to low concentration of water
Remember: H2O moves high to low!

22. The water must move because the particles are too big to fit thru the membrane

23. 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

24. 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

25. . Phagocytosis is the ingestion of bacteria or other material by phagocytes.

26. Steps: Steps of a macrophage ingesting a pathogen:
Ingestion through phagocytosis, a phagosome is formed
The fusion with lysosomes:
pathogen is broken down by enzymes c. Waste material is expelled or assimilated