1. Chapter 7.3 Cell Membrane and Cell Transport

2. Cell Membrane AKA – Plasma Membrane
Cell membrane is flexible and allows a unicellular organism to move.
Controls what enters and leaves the cell
Selectively permeable
Only certain substances (molecules) are allowed to pass through
Made of a phospholipid bilayer
Called the “Fluid Mosaic Model”

3. Phospholipid Bilayer Head Tails Hydrophobic vs Hydrophilic
Polar (charge)
Phosphate (PO4) and Glycerol
Hydrophilic (water-loving)
Pointed toward inside & outside of cell
Tails
Nonpolar (no charge)
Fatty acid chains
2 fatty acid chains (tails)
Hydrophobic (water-hating)
Pointed toward middle of membrane
Hydrophobic vs Hydrophilic
Hydrophobic – fears water
Hydrophilic – loves water

4. Homeostasis Balanced internal condition of cells
Also called equilibrium
Maintained by plasma membrane controlling what enters and leaves the cell

5. Functions of Plasma Membrane
Protective barrier
Regulates transport in and out of the cell (selectively permeable)
Allows cell recognition
Provides anchoring sites for filaments of cytoskeleton
Provides a binding site for enzymes
Interlocking surfaces bind cells together (junctions)
Contains the cytoplasm (fluid in cell)

6. Phospholipid Bilayer (sketch)

7. What else is in the phospholipid bilayer?
Cholesterol and proteins – other 2 components of bilayer
Cholesterol/carbohydrates
Provides support and flexibility
Proteins Functions
Regulates which particles can pass across membranes
Act as enzymes in chemical reactions
Act as markers (nametags) for cell recognition and fighting off disease

8. Fluid Mosaic Model
FLUID- because individual phospholipids and proteins can move side-to-side within the layer, like it’s a liquid.
MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.

9. Cell Membrane Hydrophobic molecules pass easily; hydrophilic DO NOT.
The cell membrane is made of 2 layers of phospholipids called the lipid bilayer.
Hydrophobic molecules pass easily; hydrophilic DO NOT.

10. Solubility
Materials that are soluble in lipids can pass through the cell membrane easily.

11. Semipermeable Membrane
Small molecules and larger hydrophobic molecules move through easily. Examples: O2, CO2, H2O

12. Semipermeable Membrane
Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.

13. Movement Through the Membrane
Cell membrane monitors travel of substances across its surface.
Substances can pass the membrane wall through
Passive Transport (requiring NO energy; HIGH TO LOW)
Simple diffusion
Osmosis
Facilitated Diffusion
Active Transport (requiring energy; LOW TO HIGH).
Endocytosis
Exocytosis

15. Passive Transport 3 Types:
When molecules/ particles pass through a cell membrane WITHOUT energy; high to low concentration
3 Types:
Diffusion—movement of O2, CO2, alcohol
Osmosis—movement of H2O only
Facilitated Diffusion—movement of larger particles (glucose); need a facilitator protein

16. Simple Diffusion Simple diffusion requires no energy
Molecules move from areas of HIGH to LOW concentration

17. Diffusion
Diffusion is a PASSIVE process which means no energy is used to make the molecules move
They have a natural KINETIC ENERGY.

18. Diffusion of Liquids

19. Diffusion through a membrane
Just a reminder…..
Solute moves DOWN a concentration gradient (HIGH to LOW)

20. Osmosis Diffusion of water across a membrane
If water potential is HIGH, solute concentration is low.
If water potential is LOW, solute concentration is high.

21. Diffusion of Water Across a Membrane
High H2O potential Low solute concentration
Low H2O potential High solute concentration

22. Types of Solutions Isotonic Solution – Red Blood Cells
When the concentration is the same inside and same outside the cell.

23. Cell in Isotonic Solution
The Plasma Membrane
2/2/2019
Cell in Isotonic Solution
10% NaCl (salt) 90% H2O
ENVIRONMENT
CELL
NO NET MOVEMENT
10% NaCl (salt)
90% H2O
What is the direction of water movement?
The cell is at _______________.
equilibrium
G. Podgorski, Biol. 1010

24. Types of Solutions Hypertonic Solutions – Red Blood Cells
A hypertonic solution has a higher solute concentration than the cell

25. Cell in Hypertonic Solution
The Plasma Membrane
2/2/2019
Cell in Hypertonic Solution
15% NaCl 85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?
G. Podgorski, Biol. 1010

26. Types of Solutions Hypotonic Solution – Red Blood Cells
A hypotonic solution has a lower solute concentration than the cell

27. Cell in Hypotonic Solution
The Plasma Membrane
2/2/2019
Cell in Hypotonic Solution
10% NaCl 90% H2O
CELL
20% NaCl
80% H2O
What is the direction of water movement?
G. Podgorski, Biol. 1010

28. NO NET MOVEMENT OF H2O (equal amounts entering & leaving)
The Plasma Membrane
2/2/2019
Hypertonic Solution
Isotonic Solution
Hypotonic Solution
NO NET MOVEMENT OF H2O (equal amounts entering & leaving)
NET MOVEMENT OF WATER: GOES IN
CYTOLYSIS
NET MOVEMENT OF WATER: GOES OUT
PLASMOLYSIS
G. Podgorski, Biol. 1010

29. Cytolysis & Plasmolysis
The Plasma Membrane
2/2/2019
Cytolysis & Plasmolysis
Cytolysis
Plasmolysis
G. Podgorski, Biol. 1010

30. Facilitated Diffusion
Movement of specific molecules across cell membranes through protein channels
Examples: glucose
Needs a “carrier”protein

31. Active Transport
Active Transport - when particles (solutes) pass through a cell membrane WITH energy, but go from low to high concentration
This requires energy in the form of ATP
Requires a transport protein or “pump”
Usually found in the cell membrane
Moves AGAINST the concentration gradient

32. Active Transport
Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.
Called the Sodium-Potassium Pump

33. Moving the Big Stuff
Exocytosis – moving things out of the cell or forcing contents out of the cell.
Molecules are moved out of the cell by vesicles that fuse with the plasma membrane.
This is how many hormones are secreted and how nerve cells communicate with one another.

34. Moving the Big Stuff
Large molecules move materials into the cell by one of three forms of endocytosis.
Process of taking material into the cell by means of infoldings, or pockets, of the cell membrane.

35. Pinocytosis Most common form of endocytosis
Takes in dissolved molecules as a vesicle
Takes in liquid from the surrounding environment

36. Pinocytosis Cell forms an invagination
Materials dissolve in water to be brought into the cell
Pinocytosis - called “cell drinking”

37. Receptor-Mediated Endocytosis
Some integral proteins have receptors on their surface to recognize and take in hormones, cholesterol, and other materials.

38. Phagocytosis
Used to engulf large particles such as food, bacteria, and other materials into vesicles.
Called “cell eating”