Chapter 7

cell membrane

a plasma phospholipid bilayer controlling traffic into and out of the cell

selectively permeable

allowing some substances to cross the membrane more easily than others

lipids and proteins

staple ingredients of a membranes

amphipathic molecule

a phospholipid having a hydrophilic and hydrophobic region

fluid mosaic model

currently accepted model of a cell membrane structure. Envisions it as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.


temperature buffer

integral proteins

penetrate the hydrophobic core of the lipid bilayer

transmembrane proteins

span the entire membrane, going through all layers of the cell membrane.

peripheral proteins

not embedded into the lipid bilayer AT ALL, appendages loosely bound to the surface of the membrane, often exposed to parts of the integral proteins.

transport, enyzmatic activity, signal transduction, cell to cell recognition, intercellular joining, attachment to cytoskeleton

6 major functions performed by proteins


a.) proteins that span the membrane can provide hydrophilic channel across the membrane. b.) others shuttle a substance from one side to the other by changing shape
ex: hydrolyzing ATP as an energy to actively transport substances across the membrane.

enzymatic activity

a protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. also organize as a team to carry out metabolic pathways.

signal transduction

membrane protein called a receptor may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The signaling molecule may cause a shape change.

cell to cell recognition

some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells. distinguish one type of neighboring cell from another. basis for rejection of foreign cells.

intercellular joining

membrane proteins of adjacent cells may hook together in various kinds of junction, i.e. gap junctions or tight junctions.

attachment to cytoskeleton

microfilaments or other elements of the cytoskeleton may be noncovalantly bound to membrane proteins, this helps maintain cell shape and stabalizes the location of certain membrane protens.
*Proteins that bind to Extra Cellular Membrane molecules can coor


a lipid with a covalently attached carbohydrates., membrane carbohydrates that are covalently bonded to lipids


a protein with one or more carbohydrate covalently attached to it. distinguish one cell from another.

transport proteins

transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane, lipid bilayer acts as gate keeper.

channel proteins

function by having a hydrophilic channel that certain molecules or atomic ions use as a tunnel thru the membrane


channel protein in plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of water across the membrane.

carrier proteins

transport proteins that hold onto their passengers and change shape in a way that shuttles them across the membrane

thermal motion

molecules posses an energy called this, which results in diffusion


result of thermal motion, the movement of molecules of any substance so that they spread out evenly in the available space.

concentration gradient

the region along which the density of a chemical substance decreases

passive transport

the diffusion of a substance across a biological membrane. The cell does not ave to use energy to make it happen


the diffusion of water across a selectively permeable membrane, balance of water between cell and environment


the ability of a solution to cause a cell to gain or lose water


a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell, stableness


a solution that, when surrounding a cell, will cause the cell to lose water, causing a cell to die.


a solution that, when surrounding a cell, will cause the cell to take up water. water enters faster than it leaves causing the cell to burst

osmo regulation

control of water balance


very firm cell in plants


limp cell in plants


the cytoplasm shrivels and the plasma membrane pulls away from the cell walls, when cell loses water to a hypertonic environment.

facilitated diffusion

diffusion of molecules across the lipid bilayer with help from proteins

ion channels

funciton as gated channels which open or close in response to a stimulus

active transport

movement of a substance across a cell membrane, with an expenditure of energy. to pump and solute across a membrane against its gradient requires work!

sodium-potassium pump

1. transport protein in plasma membrane that actively transports sodium out of the cell and potassium in.

membrane potential

voltage difference across cell membrane, inside is neg and outside is positive.

electrochemical gradient

combinations of forces acting on an ion

electrogenic pump

2. transport protein that generates voltage across a membrane


3. occurs when active transport of a solute indirectly drives the transport of another solute
ex: active transport out and passive transport in


4. cell secretes certain biological molecules by the fusion of vesicles with the plasma membrane, removing from the cell


5. cell takes in biological molecules to form new vesicles from the plasma membrane.


cellular eating of solids


cellular drinking of liquids


enables cell to acquire bulk quantities of specific substances, even though those substance may not be very concentrated


any molecule that binds specifically to a receptor site of another molecule