1. Chapter 5: Biological Membranes
AP Biology
Chapter 5

2. Plasma Membrane Functions: separates the cell's insides from outside
regulates passage of materials into/out of cell
transmitting signals and info. between the cell and environment
participates in chemical reactions
essential part of energy transfer and storage systems

3. Composition:
- lipid bilayer
- proteins
- in constant motion

4. Membrane Proteins
*Important area of research: how membrane proteins function in health/disease
many are enzymes
function in transport of materials/information
connect cells together to form tissues

5. Phospholipid Bilayer
Phospholipid: 2 fatty acid chains linked to a glycerol molecule
- nonpolar, hydrophobic ends (fatty acids)
- hydrophilic ends (phosphate group)
- hydrophobic "tails" turn to inside of membrane
- hydrophilic "heads" turn to outer ends of membrane
- amphipathic - have distinct hydrophilic and hydrophobic regions

7. Phospholipid Bilayer
Hydrogen bonds form between the phospholipid "heads" and the watery environment inside and outside of the cell
Hydrophobic interactions force the "tails" to face inward
Phospholipids are not bonded to each other, which makes the double layer fluid

9. Fluid Mosaic Model
Cell membrane consists of a fluid bilayer of phospholipid molecules in which proteins are embedded
- like the tiles in a mosaic picture
NOT static - proteins can move
p.107 diagram of fluid mosaic model

10. Membrane Proteins Functions: Transport of small molecules Enzymes
Information transfer
Identification tags - allow for cell-cell recognition

11. Membrane Proteins amphipathic
Integral Proteins - firmly bound to the membrane, usually do not extend all the way through
amphipathic
hydrophilic regions extend out of the cell or into
cytoplasm
- hydrophobic regions interact with fatty acid tails of the phospholipids

13. Membrane Proteins
Transmembrane Proteins - extend through the membrane, also amphipathic

14. Membrane Proteins
Peripheral Proteins - not embedded in the lipid bilayer
located on the inner or outer surfaces of the plasma membrane
can be removed from the membrane without disrupting the structure

15. Cell Membrane is Selectively Permeable
Most membranes are permeable to small molecules and lipid-soluble or polar molecules
Water molecules may pass through the lipid bilayer
gases: such as O2 and CO2

17. Transport Across Membranes
Passive Transport - does not require energy, moves with the concentration gradient
Active Transport - requires ATP, moves against the concentration gradient

18. Simple Diffusion Process based on random motion
Particles move down concentration gradient -from an area of high concentration to low concentration
can occur rapidly
occurs until equilibrium is reached

20. Types of Diffusion:
Osmosis - diffusion of water across a selectively permeable membrane
p.114 Figure 5-11
Dialysis - diffusion of a solute across a selectively permeable membrane
p.113 Figure 5-10

21. High H2O potential
Low solute concentration
Low H2O potential
High solute concentration

22. Osmotic Pressure
the tendency of water to move into a solution by osmosis
solution with high solute concentration, low water, has a high osmotic pressure
solution with a low solute concentration, high water, low osmotic pressure

23. Isotonic - equal solute concentration
ex. blood plasma isotonic to blood cells
Hypertonic - higher solute concentration
- if a cell is placed in a hypertonic environment, water will leave the cell, the cell shrinks
- plasmolysis occurs: plasma membrane separates from cell wall
Hypotonic - lower solute concentration
- a cell placed in a hypotonic environment will gain water, swell, and possibly burst

26. Turgor Pressure
Turgor Pressure - internal pressure of cells with cell walls
Plants, Algae, and Bacteria
Enables them to withstand a low solute concentration outside the cell
Cell is hypertonic to environment
Water moves into cell, cell swells, building pressure -> turgor pressure against cell wall
Cell does not burst b/c of cell wall, resist stretching and water molecules must stop moving into the cell

27. Carrier-Mediated Transport
Membrane proteins move ions or molecules across a membrane
2 types:
1. facilitated diffusion (passive)
2. carrier-mediated active transport

28. Carrier-Mediated Transport
Facilitated diffusion - with concentration gradient, requires transport protein
energy comes from concentration gradient
ex. glucose permease - transports glucose into red blood cells

30. Carrier-Mediated Active Transport
Carrier-mediated Active Transport - movement of solutes across membrane against concentration gradient
particles must be "pumped" from region or low conc. to region of high conc.
requires energy source - ATP, and transport protein
ex. sodium-potassium pump: in all animal cells, pump sodium ions out of cell and potassium ions into cell

31. Other Types of Active Transport
large particles such as food, cell parts
requires ATP
Endocytosis and Exocytosis
Active Transport video clip

32. Exocytosis
Cell ejects waste products or hormones by the fusion of a vesicle with the plasma membrane
Vesicle releases contents from the cell

33. Endocytosis Materials are taken into the cell
Types: phagocytosis, pinocytosis
Endocytosis Video clip

34. Phagocytosis "cell eating"
cell ingests large solid particles such as bacteria and food
ex. protists, white blood cells
plasma membrane folds enclose particle, forms a vacuole, fuses, then enters the cell and fuses with lysosomes

35. Pinocytosis "cell drinking" cell takes in dissolved materials
droplets of fluid are trapped by folds in the membrane
pinch off into the cytosol as tiny vesicles
liquid is slowly transferred into the cytosol
vesicles become smaller, then disappear