1. 7.3 – Cell Membrane & Transport

2. Cell Membrane polar heads are hydrophilic – attracted to water
nonpolar tails are hydrophobic – not attracted to water
this makes the membrane “selective” in what crosses

3. cell membrane is called the lipid bilayer because it’s made of 2 layers of phospholipids

4. due to the membrane’s selective permeability, small molecules can move through easily
examples: oxygen (O2) & carbon dioxide (CO2)

5. ions and large molecules DO NOT move through the membrane on their own

6. Types of Transport across Cell Membranes

7. Material moves DOWN the concentration gradient through
Three Forms of Transport Across the Membrane
Material moves AGAINST the concentration gradient through a transport protein, using ATP (energy) from the cell.
Material moves DOWN the concentration gradient through
the phospholipids.
Material moves DOWN the concentration gradient HELPED by a transport protein.

8. Passive Transport Diffusion does NOT require energy
moves from high to low concentration
examples: oxygen diffusing into a cell & carbon dioxide diffusing out

9. diffusion is a PASSIVE process which means no EXTRA energy is used to make the molecules move - they have a natural KINETIC ENERGY

10. Diffusion of Liquids

11. Diffusion through a Membrane
cell membrane
solute moves DOWN concentration gradient (HIGH to LOW) – think sledding downhill!

12. Facilitated diffusion
Passive Transport
Facilitated diffusion
doesn’t require energy
uses transport proteins to move from high to low concentration
examples: glucose or amino acids moving from blood into a cell

13. Facilitated Diffusion
molecules randomly move through the pores in channel proteins due to kinetic energy

14. some carrier proteins do not extend through the membrane
bond and drag molecules through the lipid bilayer and release them on the other side

15. Osmosis diffusion of water across a membrane
moves from HIGH water (low solute) to LOW water (high solute)
high H2O & low solute
low H2O & high solute

16. because water is polar, osmosis happens too slowly and needs some “help”
cells contain water channel proteins called aquaporins that allow water to pass quickly
movement of water in or out of a cell creates a force called osmotic pressure

17. Cell in Isotonic Solution
10% NaCl 90% H2O
ENVIRONMENT
CELL
NO NET MOVEMENT
10% NaCl
90% H2O
What is the direction of water movement?
equilibrium
The cell is at _______________.

18. Cell in Hypotonic Solution
ENVIRONMENT
10% NaCl 90% H2O
CELL
20% NaCl
80% H2O
What is the direction of water movement?

19. Cell in Hypertonic Solution
15% NaCl 85% H2O
ENVIRONMENT
CELL
5% NaCl
95% H2O
What is the direction of water movement?

20. Cells in Solutions

21. Active Transport requires energy = ATP!
moves materials from LOW to HIGH concentration
moves AGAINST concentration gradient

22. examples: pumping sodium ions (Na+) out and potassium ions (K+) in against strong concentration gradients
called sodium-potassium pump

23. Sodium-Potassium Pump
3 Na+ pumped out for every 2 K+ pumped in

24. Moving the “Big Stuff”
endocytosis is the process where really large molecules move into the cell

25. Pinocytosis most common form of endocytosis (“cell drinking”)
takes in dissolved (liquid) molecules as a vesicle

26. transport across a capillary cell (blue)
mature transport vesicle
pinocytic vesicles forming
transport across a capillary cell (blue)

27. Receptor-Mediated Endocytosis
some proteins have receptors on their surface to recognize and take in hormones & cholesterol

29. Phagocytosis
used to engulf large particles (solids) such as food and bacteria into vesicles
called “cell eating” because this is how some organisms (like amoeba) eat their food

30. capture of bacteria cells (yellow) by a white blood cell (green)

31. opposite of endocytosis is exocytosis
large molecules that are made in the cell are released through the cell membrane to the outside
inside cell
cell environment

32. molecules are moved out of the cell by vesicles that fuse with the cell membrane
is how many hormones are secreted and how nerve cells communicate with one another

33. exocytic vesicle immediately after fusion with cell membrane

34. Homeostasis all these processes help the cell to maintain homeostasis
homeostasis is the balance between the organism and its external environment
multicellular organisms have specialized cells, each with their own job, to help maintain homeostasis

35. Receptor Proteins
these proteins in the lipid bilayer are used in intercellular communication
signal molecule binding to the receptor causes the receptor protein to release a signal to perform some action

36. diffusion: http://highered. mcgraw-hill
facilitated diffusion:
sodium-potassium pump:
endocytosis & exocytosis:
cell membrane review: