1. Cell Membranes & Movement Across Them

2. FLUID MOSAIC MODEL

3. Cell (plasma) membrane
Cells need an inside & an outside…
separate cell from its environment
cell membrane is the boundary IN
food
- sugars
- proteins
- fats
salts O2
H2O
OUT
waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
cell needs materials in & products or waste out

4. Lipids of cell membrane
Membrane is made of special kind of lipid
phospholipids
“split personality”
Membrane is a double layer
phospholipid bilayer
“attracted to water”
phosphate
inside cell
outside cell
lipid
“repelled by water”

5. Semi-permeable membrane
Cell membrane controls what gets in or out
Need to allow some materials — but not all — to pass through the membrane
semi-permeable or selectively permeable
only some material can get in or out
So what needs to get across the membrane?
sugar
lipids aa O2
H2O
salt
waste

6. Crossing the cell membrane
What molecules can get through the cell membrane directly?
fats and oils can pass directly through
lipid
inside cell
outside cell
salt
waste
but…
what about other stuff?
sugar aa
H2O

7. Cell membrane channels
Need to make “doors” through membrane
protein channels allow substances in & out
specific channels allow specific material in & out
H2O channel, salt channel, sugar channel, etc.
inside cell
H2O aa
sugar
salt
outside cell
waste

8. Protein channels Proteins act as doors in the membrane
channels to move specific molecules through cell membrane
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, aquaprorins, facilitate massive amounts of diffusion.
LOW

9. Movement through the channel
Passive Transport = High Concentration to Low Concentration & No Energy Required
- Diffusion
- Osmosis (Diffusion of Water)
- Facilitated Diffusion
Concentration gradient - a difference between concentrations in a space
Solvent (ex. Water) / Solute
(example, salt, dissolved in solvent)

10. Solutions

11. Molecules move from high to low
Diffusion
move from HIGH to LOW concentration
Move down the concentration gradient
Movement from high concentration of that substance to low concentration of that substance.

12. Diffusion Move from HIGH to LOW concentration diffusion of water
passive transport
no energy needed
diffusion of water
diffusion
osmosis

13. Moves from High  Low, until……….Equilibrium is reached
Diffusion
Moves from High  Low, until……….Equilibrium is reached

14. Simple Diffusion Move from HIGH to LOW LOW HIGH fat inside cell fat
Which way will fat move?
inside cell
fat
fat
fat
LOW
HIGH
fat
outside cell
fat
fat
fat
fat
fat
fat
fat

15. Facilitated Diffusion
Move from HIGH to LOW through a channel
sugar
sugar
inside cell
sugar
sugar
LOW
Which way will sugar move?
HIGH
outside cell
sugar
sugar
sugar
sugar
sugar
sugar
sugar

16. Diffusion Move from HIGH to LOW concentration
directly through membrane
simple diffusion
no energy needed
help through a protein channel
facilitated diffusion (with help)
Move Down the
Concentration Gradient
HIGH
LOW

17. Simple vs. facilitated diffusion
simple diffusion
facilitated diffusion
lipid
inside cell
outside cell
inside cell
outside cell
H2O
protein channel
H2O

18. Active transport
Cells may need molecules to move against or Up a concentration “hill”
need to pump “uphill”
from LOW to HIGH using energy
protein pump
requires energy
ATP
Plants have nitrate & phosphate pumps in their roots.
Why?
Nitrate for amino acids
Phosphate for DNA & membranes
Not coincidentally these are the main constituents of fertilizer.
ATP

19. Transport summary simple diffusion facilitated diffusion
ATP
active transport

20. Osmosis Movement of Water Across Cell Membrane

21. Osmosis Water is very important, so we talk about water separately
diffusion of water from HIGH concentration of water to LOW concentration of water
across a semi-permeable membrane

22. Keeping water balance
Cell survival depends on balancing water uptake & water loss
freshwater
HypOtonic
Balanced
Isotonic
Saltwater
Hypertonic

23. Equilibrium 85% water 15% solute 75% water 25% solute 50% water

24. Plasmolysis
When plant cells are placed in extremely hypertonic environment, water moves out of the cells by osmosis. This causes the plant vacuoles to shrink and the cell membrane detaches from the cell wall. This is plasmolysis. (Bendy Carrot)

26. Active Transport – Endocytosis (Pinocytosis; phagocytosis)

27. Active Transport - Exocytosis

28. Review Videos

29. https://www. youtube. com/watch. v=Svbf40z5obE https://www. youtube