2. Cell and Cell Parts Reivew videos
Inner Life of a Cell (with dramatic music)
Inner Life of a Cell (technically narrated)
Human skin cells, up close and personal
Dust mites (just for fun)
Through the virtual cell (in cell submarine with all of the key cellular processes)

3. What is the purpose of all this stuff?

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

5. Arranged as a Phospholipid bilayer
Serves as a 5-10 nm wide cellular border
sugar
H2O
salt
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
impermeable to polar molecules
waste
lipids

6. 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

7. Cell membrane is more than lipids…
Transmembrane proteins embedded in phospholipid bilayer
create semi-permeabe channels
lipid bilayer
membrane
protein channels in lipid bilyer membrane

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

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

10. 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

11. Proteins domains anchor molecule
Within membrane
nonpolar amino acids
hydrophobic
anchors protein into 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

12. H+
NH2 H+
COOH
Cytoplasm
Retinal
chromophore
Nonpolar
(hydrophobic)
a-helices in the
cell membrane
Examples
aquaporin = water channel in bacteria
Porin monomer
b-pleated sheets
Bacterial
outer
membrane
H2O H+
proton pump channel in photosynthetic bacteria
function through conformational change = protein changes shape
H2O

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 lipid bilayer, usually across whole membrane
transmembrane protein
ex: transport proteins
channels, permeases (pumps)

15. Filaments of cytoskeleton
Membrane is a collage of proteins & other molecules embedded in the fluid matrix of 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
1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model

16. Membrane carbohydrates
Play a key role in cell-cell recognition
ability of a cell to distinguish one cell from another
antigens
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.

17. Any Questions??

18. Movement across the Cell Membrane

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

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

21. 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”

22. 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
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”

23. 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

24. 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 proton pump
requires ATP
ATP

25. How Ion Pumps Maintain Membrane Potential
Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane
A chemical force (the ion’s concentration gradient)
An electrical force (the charge difference due to ion imbalance)
© 2011 Pearson Education, Inc.

26. © 2011 Pearson Education, Inc.
An electrogenic pump is a transport protein that generates voltage across a membrane
The sodium-potassium pump is the major electrogenic pump of animal cells
The main electrogenic pump of plants, fungi, and bacteria is a proton pump
Electrogenic pumps help store energy that can be used for cellular work (example?)
© 2011 Pearson Education, Inc.

27. Figure 7.20 A proton pump. ATP   EXTRACELLULAR FLUID   H
CYTOPLASM 27

28. Sucrose-H cotransporter
Figure 7.21
Cotransport: Coupled Transport by a Membrane Protein
ATP H   H
Proton pump H H   H H H   H
Sucrose-H cotransporter
Diffusion of H
Figure 7.21 Cotransport: active transport driven by a concentration gradient.
Sucrose  
Sucrose 28

29. Transport summary simple diffusion facilitated diffusion
ATP
active transport

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

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

32. The Special Case of Water post lab

33. 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
across a semi-permeable membrane

34. 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

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

36. 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

37. Pumping water out
Contractile vacuole in Paramecium
ATP

38. 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

39. 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

40. 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

41. Do you understand Osmosis…
Plasmolysis of onion cells video
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

42. Any Questions??

43. Review vids
Crash Course Biology
Another including transport