1. Cell Membrane & Cell Transport

2. TEM picture of a real cell membrane.
About Cell Membranes*
All cells have a cell membrane
Functions:
Controls what enters and exits the cell to maintain an internal balance called homeostasis
Provides protection and support for the cell
TEM picture of a real cell membrane.

3. Cell Membranes are made of a PHOSPHOLIPID bilayer which is
Amphipathic –
Molecules with
both hydrophilic
and hydrophobic regions
phosphate
hydrophilic
lipid
hydrophobic

4. PHOBIC TAILS in center determine what can pass through

5. *More than just a barrier…
Expanding our view of cell membrane beyond just a phospholipid bilayer barrier
phospholipids plus…

6. *A membrane is a collage of different proteins & carbohydrates & cholesterol embedded in the fluid matrix of the lipid bilayer
The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.

7. *Fluid Mosaic Model of the cell membrane
Polar heads love water & dissolve.
Membrane movement animation
Non-polar tails hide from water.
Carbohydrate cell markers
Proteins

8. Membrane Proteins
Proteins determine most of membrane’s specific functions
cell membrane & organelle membranes each have unique collections of proteins
Membrane proteins:
peripheral proteins = loosely bound to surface of membrane
integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane protein

9. Membrane Carbohydrates
Attached to proteins (glycoproteins) or lipids (glycolipids)
Play a key role in cell-cell recognition
ability of a cell to distinguish neighboring cells from another
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.

10. Types of Cellular Transport
high
low
Wee!!!
Passive Transport
cell doesn’t use energy
Diffusion
Facilitated Diffusion
Osmosis
Active Transport
cell does use energy
Protein Pumps
Endocytosis
Exocytosis
high
low
This is gonna be hard work!!

11. *Molecules need to move across membranes in cells
OUT
waste
ammonia
salts
CO2
H2O
products IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
Image modiified from:

12. Small non-polar molecules (O2 & CO2) and hydrophobic molecules (fats & other lipids)
can slip directly through the phospholipid cell membrane, but…
*Diffusion: movement directly through membrane. What molecules can get through directly?
inside cell
outside cell
lipid O2
salt
NH3
What about
other stuff?
sugar aa
H2O

13. Diffusion Passive transport High to low concentration
No energy needed
High to low concentration
Small, nonpolar molecules
Continues until equilibrium and then moves randomly

14. *Diffusion 2nd Law of Thermodynamics governs biological systems
Universe tends towards disorder
Animatioin from:
Movement from high concentration of that substance to low concentration of that substance.
Diffusion
movement from [higher]  [lower] concentration

15. *Diffusion will also happen across a cell membrane as long as there is a difference in concentration and the membrane will let the molecule pass through until equilibrium and then moves randomly

16. The Special Case of Water Movement of water across the cell membrane = OSMOSIS

17. Osmosis is diffusion of water
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
Passive
Uses no energy

18. 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

19. What will happen to an animal cell placed in different solutions?
Solute concentration
Greater outside
than inside
Lower outside
than inside
Equal outside
and inside
HYPERTONIC
HYPOTONIC
ISOTONIC
What will happen to an animal cell
placed in different solutions?

20. *How Organisms Deal with Osmotic Pressure
Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure.
A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.
Salt water fish pump salt out of their specialized gills so they do not dehydrate.
Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

21. *Grocery stores spray water on their veggies to “plump them up”

22. Animal cells = CYTOLYSIS = CRENATION

23. Plant cells = PLASMOLYSIS Cell wall keeps plant cell from bursting
Plant cells
Cell wall keeps
plant cell from bursting
= PLASMOLYSIS

24. *Loss of water from central vacuole= plants “wilt”
*Loss of water from central vacuole= plants “wilt”
Vacuole full of water gives plant support (turgor pressure)
Turgid = very firm
Flaccid = limp

25. *Managing water balance
Isotonic
animal cell immersed in isotonic solution
blood cells in blood
no net movement of water across plasma membrane
water flows across membrane, at same rate in both directions
volume of cell is stable

26. Facilitated diffusion
Move from HIGH to LOW concentration with aid of membrane transport proteins
passive transport
no energy needed
facilitated = with help
Medium size molecules;
monomers

27. Ion Channels
Move from HIGH to LOW concentration with aid of membrane transport proteins
- passive transport
- no energy needed
facilitated = with help
Small, charged molecules

28. *Carriers and Channels are specific
inside cell aa
sugar
H2O
NH3
salt
outside cell
. . . BUT STILL MOVES FROM [HIGHER] to [LOWER]

29. Active transport
Uses energy from ATP to move molecules against concentration gradient
Moves from [lower] → [higher]
Uses protein pumps OR
vesicles
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.
Animations from:

30. Active transport SODIUM-POTASSIUM PUMP
Sets up difference in charge across membranes
Pumps 3 Na+ out and 2 K+ in
Makes cells more + outside more - inside
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.
Animation from:

31. *BULK TRANSPORT ACTIVE transport Uses vesicles Requires energy (ATP)
Animation from:

32. receptor-mediated endocytosis
“Cell eating” large molecules;
whole cells
phagocytosis
“Cell drinking”
Fluids;
Small molecules
pinocytosis
triggered by ligand signal
receptor-mediated endocytosis

33. *PHAGOCYTOSIS “Cell eating” takes in large molecules; whole cells
Animation from:
“Cell eating” takes in large molecules;
whole cells
See phagocytosis
in action:

34. *Example in cells: WHITE BLOOD CELL ENGULFING BACTERIA using Phagocytosis

35. *PINOCYTOSIS “Cell drinking” Takes in fluids; Small molecules

36. EXOCYTOSIS Active transport (requires ATP) Uses vesicles
Releases substances to outside
INSULIN being released by pancreas cells using exocytosis

37. *GOLGI BODIES USE EXOCYTOSIS
Video:
*GOLGI BODIES USE EXOCYTOSIS
Animation from:

38. *Transport summary

39. *PROBLEM for Cells? Cell membranes are SELECTIVELY PERMEABLE