1. Membrane Structure & Function

2. Jobs of the cell membrane
Isolate the cytoplasm from the external environment
Regulate the exchange of substances
Communicate with other cells
Identification

3. Membrane structure Semi-permeable barrier Phospholipid bilayer
few molecules are allowed across while keeping the majority of produced chemicals inside the cell
Phospholipid bilayer
phospholipids aligned tail to tail
Amphipathic
hydrophobic region forms between the hydrophilic heads on the inner and outer surfaces

4. Fluid-mosaic model~
Proteins (the mosaic) are embedded in lipids (the fluid)
Phospholipids are not bonded to each other, which makes the double layer fluid

5. Membrane structure Phospholipids~ membrane fluidity
Cholesterol~ membrane stabilization
Membrane carbohydrates ~ cell to cell recognition
Oligosaccharides (cell markers)
Glycolipids
Glycoproteins
Membrane proteins ~ transport / communication

6. Membrane Proteins 2 types: Integral proteins~ transmembrane proteins
Peripheral proteins~ surface of membrane

7. Membrane protein function:
Transport Proteins –
regulate movement of substance
Carrier Proteins-
"grabs" certain molecules and pulls them into the cell
Gated Channels –
similar to carrier proteins, not always "open"
Enzyme activity –
control metabolic pathways
Receptor Proteins – (Signal Transduction)
set off cell responses (release of hormones or opening of channel proteins)
Recognition Proteins –
idenitfy cells to the immune system

8. Transport Proteins: Uniport - one molecule in one direction.
Symport - Two different molecules in one direction.
Antiport - Two molecules in opposite directions.

9. Transport Across Membrane
2 types:
Passive transport
No energy
Active transport
energy

10. Traffic of molecules across the membrane
Pass freely:
Hydrophobic molecules (Hydrocarbons and O2)
Small polar uncharged molecules (H2O and CO2)
Pass with help:
Ions ( H+, Na+, Cl-).
Can’t pass:
Large polar uncharged molecules (sugar)

11. Passive Transport
Diffusion of a substance across a biological membrane
Diffusion ~
molecules move from high concentration to low concentration
down a concentration gradient
Facilitation Diffusion ~
assisted by proteins (channel or carrier proteins)
Osmosis~
the diffusion of water across a selectively permeable membrane

12. A substance will diffuse from where it is more concentrated to where it is less concentrated, down its concentration gradient.
Each substance diffuses down its own concentration gradient, independent of the concentration gradients of other substances.
The concentration gradient represents potential energy and drives diffusion.
Diffusion Movie

13. Water balance Osmoregulation~ control of water balance
Solution~ mix of solute (dissolved) and a solvent (dissolving)
Hypertonic~ solution with higher concentration of solutes
Hypotonic~ solution with lower concentration of solutes
IMPORTANT: The hypertonic solution has a lower water concentration than the hypotonic solution
Isotonic~ equal concentrations of solutes

14. Water balance in living cells
Cells with Walls in environment:
Hypotonic = Turgid (very firm)
Isotonic = Flaccid (limp)
Hypertonic = Plasmolysis~ plasma membrane pulls away from cell wall
Cells without Walls in environment:
Hypotonic = Lyse (explode)
Isotonic = Normal
Hypertonic = Crenate (Shrivel)

15. Specialized Transport
Active transport~ movement of a substance against its concentration gradient with the help of cellular energy
Low  High

16. Types of Active Transport
Sodium-potassium pump
Actively maintains the gradient of Na+ and K+ ions across the membrane
Antiport
energized by ATP
Neurons use sodium-potassium pumps
Proton Pump
transports Hydrogen ions
Chloroplasts and Mitochondria

17. Endocytosis and Exocytosis
Endocytosis and Exocytosis
Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane
Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane
Phagocytosis (solid)
Pinocytosis (liquid)
receptor-mediated endocytosis (specific materials)