1. HW 1: Finish reading Ch 4 and complete Guided Reading w/s HW 2: Ch 4 SAQ # 1-8
Monday
Review and take TEST on Ch. 1 – you will need tiny rulers and calculators
Read pp. 73 – 80 Write 10 important facts
Watch: Bozeman cell membrane
P. 75 Draw, label, color, learn the bottom diagram of the fluid mosaic model of a membrane

2. HW 1: Finish reading Ch 4 and complete GR w/s HW 2: Ch 4 SAQ # 1-8
Wednesday
Potato Lab ( 1 hour of waiting)
Test return and review
Notes from the PowerPoint (first ½)
Phospholipid coloring worksheet

3. Friday Warmup: Go over HW # 1-8
HW 1: Finish reading Ch 4 and complete GR w/s HW 2: Ch 4 SAQ # Quiz Monday – Cell Membrane
Friday Warmup: Go over HW # 1-8
Finish PowerPoint notes on cell transport
Watch: Bozeman Cell Transport
Watch: Osmosis and Water Potential
Osmosis problems Elodea Lab – 45 minutes

4. Aaaah, one of those structure–function
Phospholipids
Phosphate
Phosphate head
hydrophilic
Fatty acid tails
hydrophobic
Arranged as a bilayer
“attracted to water”
Fatty acid
“repelled by water”
Aaaah, one of those structure–function
examples

5. Arranged as a Phospholipid bilayer
Serves as a cellular barrier / border
sugar
H2O
salt
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
impermeable to polar molecules
polar
hydrophilic
heads
waste
lipids

6. Cell membrane defines cell
Cell membrane separates living cell from aqueous environment
thin barrier = 8nm thick
Controls traffic in & out of the cell
allows some substances to cross more easily than others
hydrophobic (nonpolar) vs. hydrophilic (polar)

7. Permeability to polar molecules?
Membrane becomes semi-permeable via protein channels
specific channels allow specific material across cell membrane
inside cell
H2O aa
sugar
salt
outside cell
NH3

8. Cell membrane is more than lipids…
Transmembrane proteins – aka integral proteins - embedded in phospholipid bilayer
create semi-permeabe channels
lipid bilayer
membrane
protein channels in lipid bilayer membrane

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

10. nonpolar & hydrophobic
Classes of amino acids
What do these amino acids have in common?
nonpolar & hydrophobic

11. I like the polar ones the best!
Classes of amino acids
What do these amino acids have in common?
I like the polar ones the best!
polar & hydrophilic

12. Proteins domains anchor molecule
Within membrane
nonpolar amino acids
hydrophobic
anchors protein in membrane
On outer surfaces of membrane in fluid
polar amino acids
hydrophilic
extend into extracellular fluid & into cytosol
Polar areas
of protein
Nonpolar areas of protein

13. Many Functions of Membrane Proteins
“Channel”
Outside
Plasma
membrane
Inside
Transporter
Enzyme activity
Cell surface receptor
“Antigen”
Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made.
Cell surface identity marker
Cell adhesion
Attachment to the cytoskeleton

14. Membrane Proteins Proteins determine membrane’s specific functions
cell membrane & organelle membranes each have unique collections of proteins
Classes of membrane proteins:
peripheral proteins
loosely bound to surface of membrane
ex: cell surface identity marker (antigens)
integral proteins
penetrate bilayer, usually across whole membrane
transmembrane protein ex: transport proteins
channels, permeases (pumps)

15. Cell membrane must be more than lipids…
In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer
It’s like a fluid… It’s like a mosaic…
It’s the Fluid Mosaic Model!

16. Filaments of cytoskeleton
Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer
Glycoprotein
Extracellular fluid
Peripheral
protein
Glycolipid
Transmembrane
proteins
Phospholipids
Filaments of cytoskeleton
Cholesterol
Cytoplasm
The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.
1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model

17. Phospholipids – Separate dissolved ions
Facts to know:
Phospholipids – Separate dissolved ions
Proteins – Transport large molecules, pump ions
Cholesterol – Stabilize the hydrophobic lipid area
Glycoproteins and glycolipids – Identity markers for cell recognition (think antibodies)
The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.

18. Membrane carbohydrates
Play a key role in cell-cell recognition
ability of a cell to distinguish one cell from another
antigens
important in organ & tissue development
basis for rejection of foreign cells by immune system
The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells.

19. Membrane cholesterol Anchors the lipids together Stabilizes
hydrophobic
areas
The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells.

20. Any Questions??

21. Movement across the Cell Membrane

22. Diffusion 2nd Law of Thermodynamics governs biological systems
universe tends towards disorder (entropy)
Diffusion
movement from HIGH  LOW concentration
Movement from high concentration of that substance to low concentration of that substance.

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

24. Facilitated Diffusion
Diffusion through protein channels
channels move specific molecules across cell membrane
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”

25. conformational change
Active Transport
Cells may need to move molecules against concentration gradient
conformational shape change transports solute from one side of membrane to other
protein “pump”
“costs” energy = ATP
conformational change
LOW
HIGH
ATP
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.
“The Doorman”

26. Getting through cell membrane
Passive Transport
Simple diffusion
diffusion of nonpolar, hydrophobic molecules
lipids
HIGH  LOW concentration gradient
Facilitated transport
diffusion of polar, hydrophilic molecules
through a protein channel
Active transport
diffusion against concentration gradient
LOW  HIGH
uses a protein pump
requires ATP
ATP

27. Transport summary simple diffusion facilitated diffusion
ATP
active transport

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

29. Endocytosis fuse with lysosome for digestion phagocytosis
non-specific process
pinocytosis
triggered by molecular signal
receptor-mediated endocytosis

30. The Special Case of Water – OSMOSIS Movement of water from a region of higher water potential to a region of lower water potential through a partially permeable membrane. It requires no ATP

31. Osmosis is just diffusion of water
Diffusion of water from HIGH concentration of water to LOW concentration of water
across a semi-permeable membrane

32. 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

33. Managing water balance
Cell survival depends on balancing water uptake & loss
Extremely high H2O
potential
Normal H2O potential
Extremely low H2O
potential
freshwater
balanced
saltwater

34. Managing water balance
Water potential = pressure of H2O trying to leave a solution and come into the cell
Extremely high H2O
potential
Normal H2O potential
Extremely low H2O
potential
freshwater
balanced
saltwater

35. Managing water balance1
Managing water balance
Hypotonic
a cell in fresh water
high concentration of water around cell
problem: cell gains water, swells & can burst
example: Paramecium
ex: water continually enters Paramecium cell
solution: contractile vacuole
pumps water out of cell
ATP
plant cells
turgid = full cell wall protects from bursting
KABOOM!
ATP
No problem, here
freshwater

36. Pumping water out
Contractile vacuole in Paramecium
ATP

37. Managing water balance2
Managing water balance
Hypertonic
a cell in salt water
low concentration of water around cell
problem: cell loses water & can die
example: shellfish
solution: take up water or pump out salt
plant cells
plasmolysis = wilt
can recover
I’m shrinking, I’m shrinking!
I will survive!
saltwater

38. Managing water balance3
Managing water balance
Isotonic
animal cell immersed in mild salt solution
no difference in concentration of water between cell & environment
problem: none
no net movement of water
flows across membrane equally, in both directions
cell in equilibrium
volume of cell is stable
example: blood cells in blood plasma
slightly salty IV solution in hospital
That’s perfect!
I could be better…
balanced

39. Aquaporins 1991 | 2003 Water moves rapidly into & out of cells
evidence that there were water channels
protein channels allowing flow of water across cell membrane
Peter Agre
John Hopkins
Roderick MacKinnon
Rockefeller

40. 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

41. Any Questions??