1. Cell Membrane Structure
Plasma membrane: outer membrane: defines the cell
Fluid mosaic model
Phospholipid bilayer
Hydrophilic (water loving) polar heads of phospholipid molecule
Hydrophobic (water fearing) non-polar tails
Proteins
Integral proteins: go all the way through the membrane
Membrane gates and channels, receptors
Peripheral proteins: attached to only 1 side of membrane
May be found in layer facing cytoplasm
May be found in layer
facing outside of cell
Enzymes, Receptors
Some proteins and phospholipids
have carbohydrate parts attached
Glycoproteins
Glycolipids

2. Passive Transport vs. Active Transport
Passive = without adding energy
Watching TV is passive (but it is NOT transport)
Active = energy must be added
Playing soccer is active (but it is also NOT transport)

3. Passive Transport Does not require energy at the point of transport
But some force is at work
Moves substances from where they are in high concentration to where they are in low concentration
Move down the concentration gradient

4. Types of Passive Transport
Diffusion
Random movement of molecules
Does not REQUIRE movement through a membrane, but it CAN BE through a membrane
Moves substances from where they are in high concentration to where they are in low concentration until equilibrium is reached
Gasses, liquids and solids can all diffuse, but solids take a LONG time!
Some materials can diffuse through some membranes
Lipids can diffuse through cell membranes

5. Types of Passive Transport
Facilitated diffusion
Diffusion through a membrane, but where a “door” is needed
When ions, proteins and other non-lipids move through membranes, they usually need to go through a gate or channel
Gate or channel is also called a carrier protein molecule

6. Types of Passive Transport
Osmosis
Movement of WATER across a selectively permeable membrane, from where water is in high concentration to where water is in low concentration
Water can move through but the dissolved substances can’t
It may be easier to think of the other substances’ concentration
Water moves toward the higher concentration of dissolved substances
Each dissolved particle exerts about the same amount of osmotic pressure
How many osmotic particles per molecule? (hint: ionic or covalent bonds?)
Glucose, NaCl, CaCl2, a protein

7. Osmosis , cont.
When one side of the membrane has a higher concentration of dissolved substances, that side is said to be hypertonic to the other side
When one side of the membrane has a lower concentration of dissolved substances, that side is said to be hypotonic to the other side
When both sides of the membrane have the same amount of dissolved substances, they are said to be isotonic to each other
The substances on either side DO NOT have to be the same substances ( for example- salt on one side of membrane and sugar on the other side)

8. Osmosis , cont.
Physiologic condition (PC) = the normal osmotic pressure of body fluids
PC is isotonic to 5.0% glucose solution
PC is isotonic to 0.9% NaCl solution
But body fluids do NOT have 5% glucose and/or 0.9% NaCl!
(a) A red blood cell in an isotonic solution looks normal, because the same amount of water moves into the cell as moves out
(b) A red blood cell in a hypertonic solution - more water moves out of the cell than moves in, so it shrinks (crenates)
(c) A red blood cell in a hypotonic solution - more water moves into the cell than moves out, so it swells & may burst (hemolysis)

9. Osmosis in Plants
Turgor pressure results when plant cells are placed in hypotonic solution
Central water vacuole gains water
Cytoplasm expands
Plasma membrane pushes against cell wall (cell does NOT burst)
Maintains plant’s upright posture
Plasmolysis results when plant cells are placed in hypertonic solution
Central water vacuole
loses water
Plasma membrane pulls
away from cell wall

10. Active Transport
Requires energy in the form of ATP at the point of transport
Moves substances across a membrane from where they are in low concentration to where they are already in high concentration
Move against the concentration gradient

11. Types of Active Transport
Active Membrane Transport
Movement of materials across a cell membrane against the concentration gradient, using a carrier protein that bonds to ATP
Bonding causes the protein to change shape
May move one substance in one direction (uniport), or two substances in the same direction (symport) or two substances in opposite directions (antiport)
The Na+/K+ pumps are an example (they move the ions in opposite directions = antiport)

12. Types of Active Transport
The “–cytosis family”
Endocytosis
Moves materials into the cell by having the membrane engulf them and form a vesicle around them (selective membrane fusion)
Pinocytosis = “cell drinking”
Phagocytosis = “cell eating”
Exocytosis
Moves materials out of the cell by surrounding them in a membrane (vesicle formation) and merging the vesicle to the plasma membrane (selective membrane fusion)
Secretion is a type of exocytosis

13. Types of Active Transport
Special application of endocytosis:
Receptor mediated endocytosis
Essentially just endocytosis, but with special receptor proteins that trigger the formation of the vesicle