1. Cytoskeleton Functions Mechanical support Maintain shape
Movement of the cell
Movement of things inside the cell (motor molecule – carry things on “rails”)

2. Microtubules – hollow rods, walls made of tubulin – globular protein
Structures
Microtubules – hollow rods, walls made of tubulin – globular protein
Serves as tracks for motor molecules
Make up centrioles & basal bodies (9 + 0)
Interior of cilia & flagella (9 + 2)
Built to resist compression
Microfilaments – solid rods, built from actin – globular protein
Bear tension – pulling
Maintain cell shape
With myosin, causes muscle contraction,
Pinching in of cleavage furrow
Amoeboid movement (pseuodopods)
Intermediate filaments – more permanent
Made from fibrous proteins
Scaffold for attachment of organelles, cell shape that is fairly permanent

4. Plasma Membrane – Fluid Mosaic Model
Phospholipid bilayer – hydrophobic interactions
hold phospholipids and proteins together
Plasma membrane is selectively permeable (semi-permeable)

5. Cholesterol – stabilizes membranes at moderate temps and hinders solidification at low temperatures (animal cell membranes)
Carbohydrates – attached to lipids (glycolipids) or proteins (glycoproteins)
Serve as ID for cells so they can be recognized

6. Proteins –
Integral proteins - have hydrophobic sides to hold them in position
Peripheral proteins – attached to hydrophilic part of membrane – often attached to integral proteins
Functions of proteins
Transport
Enzyme
Receptor for hormones or other chemical messengers
Junction between cells (tight junctions, desmosomes, etc.)
Glycoproteins are ID tags
Attachments to cytoskeleton & extracellular matrix

8. Transport Across Membranes
Passive Transport
Diffusion – Net movement of molecules by their own kinetic energy from an area of high conc. to low conc. (down concentration gradient)
Continues until equilibrium is reached
Molecules that can do this (oxygen, carbon dioxide, alcohols (lipid soluble)

9. Osmosis – diffusion of water across membrane
Hypertonic solution (more solute)
Hypotonic solution (less solute)
Isotonic solution (equal solute conc.)
Many cells live in isotonic environments
Protists in hypotonic environment may have contractile vacuoles to excrete water
Freshwater fish excrete water through kidneys
Plant cells have cell walls that prevent lysing (bursting) of cells. The pressure the membranes exert against the cell walls is turgor pressure. This pressure keeps the green parts of the plant turgid.
Lose turgor pressure – they become flaccid
Lose more water - plasmolysis

11. Facilitated diffusion – transport protein either provides channel or binds and bends to allow molecules through (faster than they would otherwise) – channels may be gated

12. Active Transport – expenditure of energy to transport against a gradient
Sodium-Potassium pump - creates a
concentration and electrical charge difference
3 Na+ out and 2 K+ in
Glucose pumping into storage cells (liver)
Proton pump (H+ ions) – they are pumped to one side of the membrane & create electrochemical gradient. The H+ may diffuse back through specific protein channels.

14. Endocytosis & Exocytosis
Exocytosis – vesicle from Golgi fuses with plasma membrane & releases contents
Secretion of hormones, release of neurotransmitters, release of cell wall material, release of digestive enzymes
Endocytosis – vesicle forming & bringing substances inward
Phagocytosis – pseudopodia engulf visible particles, lysosomes fuse & digest the particle
Pinocytosis – pseudopodia engulf liquid