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phospholipid bilayer
what is the framework of a membrane?
phospholipid bilayer
the basic framework of a biological membrane, consisting of. two layers of phospholipids.
hydrophilic
which region of the phospholipid bilayer faces water?
hydrophobic
which region of the phospholipid bilayer faces inward toward the membrane interior?
leaflet
half of a phospholipid bilayer
fluid-mosaic model
the accepted model of a biological membrane; its basic framework is the semifluid phospholipid bilayer with a mosaic of proteins
asymmetrical
the two leaflets are ______, with different amounts of each component
lipids, proteins, and carbohydrate
the membrane is considered a mosaic of what molecules?
lipids and proteins
the membrane resembles a fluid because ______ and _______ can move relative to each other within the membrane
transmembrane proteins
a protein that has one or more regions that are physically embedded in the hydrophobic interior of a membrane’s phospholipid bilayer
lipid-anchored proteins
a type of integral membrane protein that is attached to the membrane via a lipid molecule
integral membrane protein
a protein that cannot be released from the membrane unless the membrane is dissolved with an organic solvent or detergent
transmembrane and lipid-anchored proteins
what are the two types of integral membrane proteins?
peripheral membrane protein
a protein that is noncovalently bound to a region of an integral membrane protein that projects out from the membrane or noncovalently bound to the polar head group of a phospholipid
20-30%
what percent of all genes are estimated to encode transmembrane proteins?
transmembrane proteins
computer programs can be used to predict the number of that in an organism based on DNA sequence data of an organism’s genome?
cystic fibrosis
a lung disease caused by a problem with transmembrane proteins in membranes
function
what of many genes is unknown but study may provide a better understanding an better treatments for disease?
fluidity
a property if biological membranes in which individual molecules remain in close association yet have the ability to move rotationally or laterally within the plane of the membrane
semifluid
membranes are ____
long axes
lipids can rotate freely around their what?
membrane leaflet
lipids can move laterally within the what?
semifluid
a property of biological membranes in which the movement of membrane components occurs in two dimensions
flip-flop
which type of lipids from one leaflet to the opposite does not occur spontaneously?
ATP
flippase requires ___ to transport lipids between leaflets
lipid raft
in a membrane, a group of lipids, sometimes including associated proteins, that float together as a unit in a larger sea of lipids
length of phospholipid tails, double bonds, cholesterol
what are the three factors that affect fluidity?
length of phospholipid tails
shorter tails are less likely to interact, which makes the membrane more fluid
presence of double bonds
double bond creates a kink in the fatty acid tail, making it more difficult for neighboring tails to interact and making the bilayer more fluid
presence of cholesterol
cholesterol stabilizes membranes; effects vary depending on temperature
unsaturated
the property of certain lipids that contain one or more C=C double bonds
lipids
in eukaryotes, the cytosol and end-membrane system work together t synthesize what?
lipid exchange proteins
a protein that extracts a lipid from one membrane, diffuses it through the cell, and inserts the lipid into another membrane
flippase
phospholipids change leaflets with the help of what?
glycosylation
the covalent attachment of carbohydrates to a protein or lipid, producing a glycoprotein or glycolipid
glycolipid
a lipid that has a carbohydrate attached to it
glycoprotein
a protein that has a carbohydrate attached to it
cell surface recognition
glycolipids and glycoproteins ofter play a role in what?
n-linked glycosylation
attachment of carbohydrates to nitrogen atoms of asparagine side chain
o-linked glycosylation
addition of sugars to oxygen atoms of serine for threonine side chains
o-linked
which type of glycosylation occurs only in Golgi?
membrane transport
the movement of ions or molecules across a biological membrane
selective permeability
the property of membranes that allows the passage of certain ion or molecules but not others
passive transport
the diffusion of a solute across a membrane in a process that is energetically favorable and does not require an input of energy
simple and facilitated diffusion
which two types of membrane transport is passive transport?
simple diffusion
when a substance moves across a membrane from a region of higher concentration to a region of lower concentration, without a transport protein
facilitated diffusion
a mechanism of passive transport in which a transport protein provides a passageway for a substance to cross a membrane from an area of higher concentration to a lower concentration; uses the aid of a transport protein
active transport
the transport of a substance across a membrane from an area of low concentration to one of higher concentration with the aid of a transport protein; requires an input of energy
hydrophobic interior
the barrier to hydrophilic molecules or ions is due to what?
rate of diffusion
what depends on the chemistry of a solute and its concentration?
size, polarity, charge, concentration
what are the four factors accepting the rate of diffusion across membranes?
high permeability
what occurs with gases and small uncharged molecules?
moderate permeability
what occurs with water and urea?
low permeability
what occurs with polar organic molecules?
very low permeability
what occurs with ions, charged polar molecules, and large molecules?
transmembrane gradient
a situation in which the concentration of a solute is higher on one side of a membrane than on the other
electrochemical gradient
a dual gradient across a membrane, having both electrical and chemical components; determines the direction in which ions will move
osmosis
the movement of water across a membrane to balance solute concentrations
osmotic pressure
the tendency for water to move into any cell
isotonic
condition in which the solute concentrations on both sides of a plasma membrane are equal, which does not cause a cell to shrink or swell
hypertonic
when the concentration of solutes outside cell is higher and causes a cell to shrink due to osmosis of water outside the cell
hypotonic
when the concentration of solutes outside the cell is lower and causes a cell to swell due to the uptake of water via osmosis
plasmolysis
the shrinkage of algal or plant cytoplasm that occurs when the water leaves the cell by osmosis, with the result that the plasma membrane no longer presses on the cell wall
crenation
shrinkage of a cell in a hypertonic solution
osmotic lysis
swelling and bursting of a cell in a hypotonic solution
cell wall
what prevents major changes in a cell size
hypotonic to hypertonic
how does water move during osmosis?
turgor pressure
pushes plasma membrane against cell wall
hypotonic
freshwater protists survive in what type of environment?
contractile vacuoles
to prevent osmotic lysis, what takes up water and discharges it outside of the cell
cell volume
using vacuoles to remove excess water maintains a constant what?
channel
a transmembrane protein that forms an open passageway for the facilitated diffusion of ions or molecules across a membrane
transporters
a transmembrane protein that binds tp a solute and undergoes a conformational change to allow the movement of the solute across a membrane
channels and transporters
what are the two classes of transport proteins based on their type of movement?
gated
a property of many channels that allows them to open and close to control the movement of solutes across a membrane
lignands
an ion or molecule that binds to a protein, such as an enzyme, a receptor, or a channel
lignands
gated channels are controlled by binding of small molecules called what?
Peter agre
who first identified a protein that was abundant on bed blood cells, bladder, and kidney cells?
aquaporin
since it forms a channel that allows water to pass through the membrane, CHIP28 was renamed what?
uniporter
a transporter that binds a single ion or molecule and transports it across a membrane
symporter
a transporter that bonds two or more ions or molecules and transports them in the same direction across a membrane
antiporter
a transporter that bonds two or more ions or molecules and transports them in opposite directions
primary active transport
a type of transport that involves a pump that directly use energy to transport a solute against a gradient
secondary active transport
a type of membrane transport that involves the utilization of a pre-existing gradient to drive the active transport of another solute