Cell Transport / Membrane Notes It is the job of the plasma membrane to be a boundary that regulate what enters and leaves the cell. This model of a membrane is called the fluid-mosaic model because it is a combination (mosaic) of molecules suspended in a fluid-like framework.

Note: 3 of the 4 biomolecules comprise the membrane.

Parts of the Plasma Membrane Phospholipid bilayer – main component Phosphate head – hydrophilic (water-loving), water soluble – dissolves in water Lipid tails – hydrophobic (fear of water), water insoluble – does NOT dissolve in water

Protein - protein channels for transport Carbohydrates - identification markers- can be attached to phospholipid or protein Cholesterol - stabilizes the membrane

Movement through Cell Boundaries: Selectively Permeable Membrane The membrane is selectively or semi-permeable – some materials can pass thru, others cannot (= membrane is impermeable to them). Permeability depends on: particle size – small molecules such as O2, CO2 and H2O pass through shape of molecules – for protein channels charge of ions (some ions are repelled)

Passive Transport Requires no energy (E) because it relies upon random particle movements. Goes with concentration gradient = (difference in concentration on either side of membrane) until equilibrium is reached (same concentration on both sides of membrane) Molecules are constantly moving, so they will move naturally with the concentration gradient.

3 Types of Passive Transport Diffusion – any material, except H2O moving from high to low concentration thru bilayer http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Passive Transport continued… 2. Facilitated Diffusion – uses protein channels to enter / leave cells ex: glucose can only enter this way It is fast, specific and requires no energy

Passive Transport continued… Osmosis – the diffusion of H2O Only water moving from a high to a low concentration until solution reaches equilibrium Osmotic pressure – pressure exerted on membrane when water moves across Note: Penicillin works because it weakens cell walls, osmotic pressure increases and causes bacteria membranes to burst.

Osmosis

Solutions (terms only apply to water movement = osmosis) Isotonic – equal conc. of solute molecules on either side of membrane; no net movement of water Hypertonic – more solute outside of cell, water moves out of cell, cell shrinks; in plants it causes plasmolysis (loss of turgor pressure) Hypotonic – less solute outside of cell, water enters cell, cell could burst.

Osmosis: Maintaining Homeostasis - the process by which organisms maintain a relatively stable, internal environment

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Cell Water Balance

Active Transport Molecules move against the concentration gradient; from low concentration to high concentration Requires energy (E) = ATP ATP (adenosine triphosphate) is the E molecule chemical produced and used by your cells

Bulk Transport – Vesicles / Vacuoles Endocytosis – cells take in particles by membrane forming a “pocket” - a vesicle / vacuole Exocytosis – releasing materials from cells in vesicles that fuse with membrane ex: vesicles of hormones, enzymes, wastes ex: vacuoles removing water or wastes; contractile vacuole in protist pump out extra water Requires ATP!