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phospholipid bilayer

the framework of the plasma membrane; consists of two layers of phospholipids


adjective describing molecules with a hydrophobic and hydrophilic region

fluid-mosaic model

name for the depiction of the membrane structure; it exhibits a fluid because lipids and proteins can move relative to each other within the membrane and is a basic mosaic of lipid, protein, and carbohydrate molecules

integral membrane protein

another name for the intrinsic membrane protein; cannot be released from the membrane unless the membrane is dissolved with an organic solvent or detergent

transmembrane protein

most common type of integral membrane protein; has one or more regions that are physically inserted into the hydrophobic region of the phospholipid bilayer

lipid anchored protein

a type of integral membrane that has a lipid molecule conveniently attached to an amino acid side chain within the protein

peripheral membrane proteins

extrinsic proteins; do not interact with the hydrophobic interior, but are non-covalently bound to regions of the integral membrane proteins that project outwards from the membrane or are bound to polar head groups of phospholipids


the process of covalently attaching a carbohydrate to a lipid or protein


a carbohydrate attached to a lipid


a carbohydrate attached to a protein

membrane transport

the movement of ions and molecules across biological membranes

selective permeability

function of the plasma membrane which ensures that essential molecules like glucose and amino acids enter the cell while metabolic intermediates remain and waste is forced to exit

facilitated diffusion

a method of allowing substance to move across membranes; a transport protein provides a passageway for the substance to cross the membrane

passive transport

the transport of a substance across a membrane from a region of high concentration to a region of lower concentration; does not require input of energy

active transport

movement from an area of high concentration to low concentration or against a concentration gradient with the aid of a transport protein

transmembrane gradient

when a concentration of a solute is higher on one side of a membrane than the other

electrochemical gradient

a dual gradient that has both electrical and chemical components; occurs with solutes that have a net positive or negative charge


the process in which water diffuses across a membrane from the hypotonic compartment into the hypertonic compartment


when the solute concentrations on both sides of the plasma membrane are equal


when the solute concentration out the cell is higher (water is lower)


when the solute concentration outside the cell is lower (water is higher)

osmotic lysis

when a cell takes up so much water that it ruptures


when water exits the cells via osmosis and equalizes solute concentrations on both sides of the cell membrane, causing them to shrink

turgor pressure

osmotic pressure; the hydrostatic pressure required to stop the net flow of water across a membrane due to osmosis

transport protein

transmembrane protein that provides a passageway for the movement of ion and hydrophilic molecules across the membranes; play major role in selective permeability


gated; forms an open passageway for the facilitated diffusion of ions or molecules across the membrane (solutes move directly through to get to the other side)


binds a single ion or molecule and transports it across the membrane


cotransporter; binds two or more ions or molecules and transports the in the same direction


binds two or more ions or molecules and transports them in opposite directions

primary active transport

involved the functioning of a pump (a type of transporter that directly uses energy to transport a solute against a gradient)

secondary active transport

involved the use of pre-existing gradient to drive the active transport of another solute

electrogenic pump

pump that generates an electrical gradient across the membrane


when material inside the cell is packaged into vesicles and then excreted into the extracellular environment (vesicles derived from Golgi apparatus)


the plasma membrane invaginates (fold inward) to form a vesicle that brings substances into the cell

receptor-mediated endocytosis

form of endocytosis; a receptor in the plasma membrane is specific for a given cargo


formation of membrane vesicles from the plasma membrane as a way for cells to internalize the extracellular fluid (small substances)


an extreme form of endocytosis involving the formation of an enormous membrane vesicle that engulfs a large particle

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