Membrane Structure & Function Ch. 7

the plasma membrane

is the boundary that separates the living cell from its surroundings

selectively permeable

the plasma membrane is __________ ___________

passive transport

(of small molecules) doesn't require energy; it may involve transport proteins

active transport

(of small molecules) requires energy and a transport protein

exocytosis

molecules are secreted when a vesicle fuses with the plasma membrane

bulk transport

moves large molecules

endocytosis

large molecules are taken in when the plasma membrane pinches inward, forming a vesicle

fluid mosaic model

the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

hydrophobic interactions

membranes are held together mainly by weak __________ __________

lipids

proteins

most of the _______ and some ______ can move sideways within the membrane

peripheral proteins

are bound to the surface of the membrane

integral proteins

penetrate the hydrophobic core

transmembrane proteins

integral proteins that span the membrane are called __________ __________

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix (ECM)

cell-surface proteins can carry out several functions (list all 6)

plasma membrane

a cell must exchange materials with its surroundings, a process controlled by the _________ __________

molecular traffic

plasma membranes are selectively permeable, regulating the cell's _________ _________

hydrophobic (non polar)

molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly

hydrophilic (polar)

molecules including ions and polar molecules do not cross the membrane easily

small non polar molecules

O2, CO2, N2

small uncharged polar molecules

H2O, NH3, glycerol

large uncharged polar molecules

glucose, sucrose

ions

Na+, K+, Cl-

transport proteins

allow passage of hydrophilic substances across the membrane; is specific for the substance it moves

carrier proteins

other transport proteins, called _______ _______, bind to molecules and change shape to shuttle them across the membrane

passive transport

is diffusion of a substance across a membrane with no energy investment

diffusion

is the tendency for molecules to spread out evenly into the available space

directional

although each molecule moves randomly, diffusion of a population of molecules may be ___________

concentration gradient (from high concentration to low concentration)

substances diffuse down their ___________ ___________

passive transport

the diffusion of a substance across a biological membrane is ________ ________ because no energy is expended by the cell to make it happen

osmosis

is the diffusion of water across a selectively permeable membrane

lower solute concentration

higher solute concentration

equal

water diffuses across a membrane from the region of ______ _______ _________ to the region of _________ __________ ___________ until the solute is ________ on both sides

ion channels

facilitate the transport of ions

gated channels

some ion channels, called _________ _________, open or close in response to stimulus

facilitated diffusion

is still passive because the solute moves down its concentration gradient, and the transport requires no energy

against

some transport proteins, however, can move solutes ________ their concentration gradients

active transport

requires energy, from ATP hydrolysis, to move substances against their concentration gradient

cotransport

coupled transport by a membrane protein; active transport driven by a concentration gradient

exocytosis and endocytosis

bulk transport across the plasma membrane occurs by __________ and __________

lipid bilayer

transport proteins

small molecules and water enter or leave the cell through the _________ ________ or via _________ _________

vesicles

large molecules, such as polysaccharides and proteins, cross the membranes in bulk via __________

energy

bulk transport requires _________

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