Chapter 4 Cells and Their Environment

Passive Transport Reminders: Phospholipid bi-layer, ATP, and proteins on bi- layer. Passive transport: is the movement across the cell membrane, that does not require energy from the cell. -All particles of matter are moving (yes everything) -This motion causes the matter to move out in all directions, bumping into other matter -It is natural, all things want balance, even the particles moving around, a desire to reach equilibrium.

Concentration gradient: a difference in the concentration of a substance, across a space. -If not hindered, all particles will move, naturally, from an area of high concentration to an area of low concentration until equilibrium is reached. -Diffusion: is the movement of a substance from an area of high concentration to an area of lower concentration. This is caused by the random motion of the particles of the substances. -Substances are constantly moving in and out of cells due to concentration levels, via the selectively permeable membrane. -Osmosis: is the diffusion of water across a selectively permeable membrane.

Diffusion explained.

Hyper, Hypo, and Iso solutions -Hypertonic: when water diffuses out of the cell, cell shrinks, therefore a solution that causes a cell to shrink is hypertonic. -Hypotonic: when water diffuses into the cell, cell swells, therefore a solution that causes a cell to swell is hypotonic. -Isotonic: There is no “net” movement of water. THIS DOES NOT MEAN THAT WATER IS NOT MOVING IN AND OUT. No “net” movement means that equal amounts of water move in AND out of the cell.

Crossing the cell membrane -review: selective permeable, transport proteins, ions -Ion Channels: is a transport protein through which ions can pass. Examples: Na+, Ca2+, Cl-. -Spans entire cell membrane -Most channels are always open -Passive transport, based on concentration gradient -Rate of movement influenced by conc. Grad. -Also, think charges, opposites attract, like repel, can effect movement as well

Facilitated Diffusion -Most substances can bind to a particular protein, to be moved in or out of a cell. -Carrier proteins: are these (see above) -Movement of substances, down their concentration gradient, via a carrier protein, is FD -Step 1: molecule binds to carrier protein -Step 2: change in shape of CP exposes substance to other side of membrane -Step 3: molecule is then released. -VERY IMPORTANT!!! Like a key to a lock, only a CP will let in a specific molecule -Example: aquaporin's only allow water molecules to pass through, nothing else.

Active Transport -ATP (energy) is required!!! -Moving against concentration gradient -Many involved carrier proteins Sodium potassium pump -Moves 3 Na+’s out of the cell -Moves 2 K+’s into the cell -Both against their concentration gradients -VERY important in cell function, especially nerve cells

Endocytosis: movement of substances into a cell by a vesicle Exocytosis: movement of substances out of a cell by a vesicle

Receptor protein: protein that binds to a specific signal molecule, enabling cell to respond to the signal molecule. Second messenger: acts as a signal molecule in the cytoplasm, often amplifies the signal of the first messenger. Enzyme action: receptor protein may act as an enzyme, example, causing reactions to speed up. Many drugs affect the binding signal, by blocking or activating signals. Can be very bad, or good.