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63 terms

Membrane structure and Function

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diffusion
when a substance moves from an area of higher concentration to an area of lower concentration; caused by entrapy because nature wants stability
osmosis
the diffusion of water through a selectively permeable membrane
dialysis
the diffusion of small solutes through a selectively permeable membrane
passive transport
diffusion or osmosis; the way a cell gets materials or excretes them by having them go from a high concentration to a low concentration; no ATP is necessary, energy comes from normal collisions; slow over large distances
active transport
when a cell gets materials or excretes them by using its own energy, usually through ATP; going against natural tendencies
hypertonic
describes a solution that has a greater concentration of total solute
hypotonic
describes a solution that has a lesser concentration of total solute
isotonic
describes solutions that have an equal concentration of total solutes
turgor pressure
the pressure inside of a cell as a cell pushes itself against the cell wall
plasmolysis
this happens when a cell shrinks inside its cell wall while the cell wall remains intact; concentration of water decreases, while solute concentration increases
flaccid
this happens when water moves, but the amount within the cell is constant; no pressure builds
cytolysis
this happens when a cell swells until pressure bursts it, resulting in cell death
crenation
this happens when a cell shrinks and shrivels; can result in cell death if severe
water potential
this states that water will always move from an area with high water potential to an area with low water potential
solute potential
this measurement has a maximum value of 0; it decreases as the concentration of a solute increases
pressure potential
this measurement has a minimum value of 0 (when the solution is open to the environment); it increases as pressure increases
selective permeability
a property of a plasma membrane that allows some substances to cross more easily than others
amphipathic
molecules are said to be this when it has regions that are both hydrophilic and hydrophobic
fluid mosaic model
the currently accepted arrangement of membranes; it is a fluid structure with a "mosaic" of various proteins embedded in or attached to a double layer of phospholipids; proposed by Singer and Nicolson in 1972
integral proteins
the proteins of a membrane that penetrate the hydrophobic core of the lipid bilayer; hydrophobic regions consist of nonpolar amino acids, while hydrophilic regions are exposed to aqueous solution on either side of membrane
transmembrane proteins
the proteins of a membrane that span the entire membrane
peripheral proteins
the proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane, often exposed to parts of the integral proteins; attached by cytoskeleton on cytoplasmic side, and by fibers of ECM on extracellular side
transport
the function of membrane proteins that allows travel through a hydrophilic channel, or by transport proteins, which shuttle molecules across the membrane by changing shape with the help of hydrolyzing ATP
enzymatic activity
the function of membrane proteins that uses the exposure of proteins' active sites to adjacent solutions; metabolic processes progress to help substances pass
signal transduction
the function of membrane proteins that allow proteins to have binding sites with specific shapes that fit chemical messengers; external messengers may cause a shape change in protein that relays a message to the inside of the cell, usually by binding to a cytoplasmic protein
cell-cell recognition
the function of membrane proteins in which some glycoproteins serve as ID tags that are recognized by membrane proteins of other cells
intercellular joining
the function of membrane proteins in which membrane proteins of adjacent cells hook together, as in gap junctions or tight junctions
attachment to cytoskeleton and extracellular matrix
the function of membrane proteins in which microfilaments bond noncovalently to membrane proteins, maintaining cell shape and protein location; proteins bound to extracellular matrix molecules can coordinate extracellular and intracellular changes
glycolipids
membrane carbohydrates that are covalently bonded to lipids
glycoproteins
membrane carbohydrates that are covalently bonded to proteins
first step
What step is this in moving a molecule from one side of the membrane to another? synthesis of membrane lipids and proteins in ER; carbohydrates are added to proteins, making them glycoproteins; the carbohydrate portion can be modified
second step
What step is this in moving a molecule from one side of the membrane to another?inside Golgi, glycoproteins undergo further carbohydrate modification, and lipids acquire carbohydrates, becoming glycolipids
third step
What step is this in moving a molecule from one side of the membrane to another? transmembrane proteins, membrane glycolipids, and secretory proteins are transported in vesicles to the plasma membrane
fourth step
What step is this in moving a molecule from one side of the membrane to another? in plasma membrane, vesicles are fused, releasing secretory proteins from the cell; vesicle fusion positions carbohydrates on the outside of the plasma membrane; asymmetrical arrangement in the plasma membrane is determined by construction in the ER and Golgi
transport protein
a membrane protein that is responsible for moving hydrophilic substances from one side to the other
channel protein
a membrane protein, specifically a transport protein, that has a hydrophilic channel that certain molecules or atomic ions use as a tunnel
aquaporin
a membrane protein, specifically a transport protein, that facilitates the passage of water through channel proteins
carrier protein
a membrane protein, specifically a transport protein, that holds onto molecules and changes their shapes in a way that shuttles them across the membrane
concentration gradient
the region along which the density of a substance decreases
up
when a substance diffuses from an area of lower concentration to an area of higher concentration, it is moving ______ its concentration gradient
down
when a substance diffuses from an area of higher concentration to an area of lower concentration, it is moving ________ its concentration gradient
tonicity
the ability of a solution to cause a cell to gain or lose water; depends partly on concentration of nonpenetrating solutes relative to inside of cell
osmoregulation
the control of water balance
turgid
a cell with a cell wall that has a reasonable amount of pressure but is healthy
flaccid
a cell with a cell wall that is in an isotonic solution that allows for a steady volume
facilitated diffusion
passive diffusion that is aided by transport proteins, but that does not require cellular energy
membrane potential
the voltage of a plasma membrane; ranges from -50 mV to -200 mV; the (-) signifies in which direction the substances move--(-) = outside of cell
membrane potential
favors the passive transport of cations into the cell and anions out of the cell
electrochemical gradient
the combination of forces that acts on membrane potential
nonpolar
when ____________ entities hit the membrane, they dissolve through it and pass through the membrane and into the cell
ionic
when ____________ entities hit the membrane, they accompany a protein in order to be dissolved, regardless of size
small nonpolar
when ____________ entities hit the membrane, they pass through the membrane alone
large polar
when ____________ entities hit the membrane, they are completely blocked from entering
gated channel
a highly selective tunnel on a plasma membrane that can open or close depending on conformational changes; they are changed due to electrical disturbances, bonding of a specific ligand; allows a substance to diffuse
electrogenic pump
a transport protein that generates voltage across a membrane, causing a net separation in charge
proton pump
an electrogenic pump that works largely with H+ ions in plants, fungi, and bacteria
cotransport
a mechanism through which a single ATP-powered pump that transports a specific solute can indirectly drive the active transport of several other solutes; substances that have been pumped across membrane can do work as they move back across the membrane by diffusion
exocytosis
occurs when a cell secretes certain biological molecules by the fusion of vesicles with the plasma membrane
endocytosis
occurs when a cell takes in biological molecules and particulate matter by forming new vesicles from the plasma membrane
phagocytosis
a type of endocytosis in which the cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane-enclosed sac that can be large enough to be considered a vacuole; particle is digested after vacuole fuses with lysosome
pinocytosis
a type of endocytosis in which the cell "gulps" droplets of fluid into tiny vesicles; molecules dissolved in liquid are necessary for cell; nonspecific in substances it transports
receptor-mediated
a type of endocytosis in which the cell acquires bulk quantities of specific substances, even though they may not be very concentrated in the extracellular fluid; receptor proteins are already clustered in regions of membrane called coated pits, which are lined on cytoplasmic side by fuzzy layer of coat proteins; when ligands bond to receptors, coated pits form a vesicle that contains ligand molecules
ligand
any molecule that bonds specifically to a receptor site of another molecule