BIOL 253 EXAM 1 QUESTIONS &
ANSWERS(GRADED A+)
universal function of membranes - ANSWERto act as a selective barrier to the
passage of molecules
functions of plasma membranes - ANSWER1. regulate passage of substances in
and out of cells and between cell organelles and cytosol
2. detect chemical messengers arriving at the cell surface
3. link adjacent cells together by membrane junctions
4. anchor cells to the extracellular matrix
fluid mosaic model - ANSWERmodel that describes the arrangement and movement
of the molecules that make up a cell membrane
lipid rafts - ANSWERcholesterol-rich regions of reduced membrane fluidity that are
believed to serve as organizing centers for the generation of complex intracellular
signals
integrins - ANSWERA transmembrane protein that interconnects the extracellular
matrix and the cytoskeleton.
Desmosomes - ANSWERAnchoring junctions that prevent cells from being pulled
apart
integral membrane protein - ANSWERclosely associated with membrane lipids
can't be extracted from the membrane without disrupting the lipid bilayer
amphipathic (polar out, nonpolar in)
some can move laterally but others can't because they are linked to peripheral
proteins
transmembrane proteins - ANSWERIntegral proteins that span the membrane.
peripheral membrane proteins - ANSWERlocated on membrane surface and are
bound to the polar regions of integral proteins
not amphipathic
glycoalyx - ANSWERlayer of sticky carbohydrates covering plasma membrane,
provides strength, attachment and cell cell recognition, anchored to the plasma
membrane by carbohydrates bonded to proteins and lipids in the membrane
,Cadherins - ANSWERproteins that extend from the cell into the extracellular space,
where they link up and bind with cadherins from an adjacent cell
tight junction - ANSWERjunction that forms between two adjacent plasma
membranes to remove extracellular space between them
occurs in a band around the entire circumference of the cell
gap junctions - ANSWERprotein channels that link the cytosols of adjacent cells
limits what can pass between the cytosols of the connected cells to small molecules
and ions
simple diffusion - ANSWERmovement of a solute from an area of high concentration
to an area of low concentration
flux - ANSWERthe amount of material crossing a surface in a unit of time
net flux - ANSWERdifference between two one-way fluxes
determines net gain for compartment 2 and net loss for compartment 1
always greater from regions of higher conc. to lower conc.
diffusion equilibrium - ANSWERstate during which diffusion fluxes in opposite
directions are equal; that is, the net flux equals zero
factors that affect net flux - ANSWER1. temperature: higher temp = faster net flux
2. mass of molecule: larger molecule = slower net flux
3. surface area: greater surface area = faster net flux
4. medium: air = faster net flux
Fick's Law of Diffusion - ANSWERJ = PA(Co-Ci)
J= rate of diffusion/magnitude of net fluc
Co= conc. outside cell
Ci= conc. inside cell
A = surface area of membrane
P= membrane permeability coefficient (larger = faster net flux)
ion channels - ANSWERallow the passage of ions across the membrane
small size prevents larger molecules from entering or leaving
show selectivity for type of ions that can pass through
, membrane potential - ANSWERthe electrical charge across a cell membrane
provides electrical force that can influence the movement of ions through their
channels across the plasma membrane
electrochemical gradient - ANSWERThe combination of forces that acts on
membrane potential.
channel gating - ANSWERprocess of opening and closing ion channels
factors that alter channel protein conformations - ANSWER1. binding of specific
molecules to channel proteins
2. changes in membrane potential
3. physically deforming the membrane
ligand-gated ion channel - ANSWERchanges shape in response to a signaling
molecule (ligand), allowing or blocking the flow of specific ions
voltage-gated ion channels - ANSWERChannels that open or close in response to a
change in the membrane potential.
mechanically gated ion channels - ANSWERopened or closed by deformation or
stretch of the plasma membrane
transporters - ANSWERintegral membrane proteins that mediate passage of
molecules through membrane
mediated transport - ANSWERmovement of molecules across membrane by binding
to protein transporter
factors that determine solute flux through mediated-transport system - ANSWER1.
solute concentration
2. affinity of transporters for solute
3. number of transporters in membrane
4. rate at which conformational change in transport protein occurs
facilitated diffusion - ANSWERthe movement of specific molecules across a cell
membrane through protein channels
high to low
active transport - ANSWEREnergy-requiring process that moves material across a
cell membrane against a concentration gradient
primary active transport - ANSWERdirect use of ATP
secondary active transport - ANSWERuse of an electrochemical gradient
Cotransport (symport) - ANSWERmovement of solute into the cell
ANSWERS(GRADED A+)
universal function of membranes - ANSWERto act as a selective barrier to the
passage of molecules
functions of plasma membranes - ANSWER1. regulate passage of substances in
and out of cells and between cell organelles and cytosol
2. detect chemical messengers arriving at the cell surface
3. link adjacent cells together by membrane junctions
4. anchor cells to the extracellular matrix
fluid mosaic model - ANSWERmodel that describes the arrangement and movement
of the molecules that make up a cell membrane
lipid rafts - ANSWERcholesterol-rich regions of reduced membrane fluidity that are
believed to serve as organizing centers for the generation of complex intracellular
signals
integrins - ANSWERA transmembrane protein that interconnects the extracellular
matrix and the cytoskeleton.
Desmosomes - ANSWERAnchoring junctions that prevent cells from being pulled
apart
integral membrane protein - ANSWERclosely associated with membrane lipids
can't be extracted from the membrane without disrupting the lipid bilayer
amphipathic (polar out, nonpolar in)
some can move laterally but others can't because they are linked to peripheral
proteins
transmembrane proteins - ANSWERIntegral proteins that span the membrane.
peripheral membrane proteins - ANSWERlocated on membrane surface and are
bound to the polar regions of integral proteins
not amphipathic
glycoalyx - ANSWERlayer of sticky carbohydrates covering plasma membrane,
provides strength, attachment and cell cell recognition, anchored to the plasma
membrane by carbohydrates bonded to proteins and lipids in the membrane
,Cadherins - ANSWERproteins that extend from the cell into the extracellular space,
where they link up and bind with cadherins from an adjacent cell
tight junction - ANSWERjunction that forms between two adjacent plasma
membranes to remove extracellular space between them
occurs in a band around the entire circumference of the cell
gap junctions - ANSWERprotein channels that link the cytosols of adjacent cells
limits what can pass between the cytosols of the connected cells to small molecules
and ions
simple diffusion - ANSWERmovement of a solute from an area of high concentration
to an area of low concentration
flux - ANSWERthe amount of material crossing a surface in a unit of time
net flux - ANSWERdifference between two one-way fluxes
determines net gain for compartment 2 and net loss for compartment 1
always greater from regions of higher conc. to lower conc.
diffusion equilibrium - ANSWERstate during which diffusion fluxes in opposite
directions are equal; that is, the net flux equals zero
factors that affect net flux - ANSWER1. temperature: higher temp = faster net flux
2. mass of molecule: larger molecule = slower net flux
3. surface area: greater surface area = faster net flux
4. medium: air = faster net flux
Fick's Law of Diffusion - ANSWERJ = PA(Co-Ci)
J= rate of diffusion/magnitude of net fluc
Co= conc. outside cell
Ci= conc. inside cell
A = surface area of membrane
P= membrane permeability coefficient (larger = faster net flux)
ion channels - ANSWERallow the passage of ions across the membrane
small size prevents larger molecules from entering or leaving
show selectivity for type of ions that can pass through
, membrane potential - ANSWERthe electrical charge across a cell membrane
provides electrical force that can influence the movement of ions through their
channels across the plasma membrane
electrochemical gradient - ANSWERThe combination of forces that acts on
membrane potential.
channel gating - ANSWERprocess of opening and closing ion channels
factors that alter channel protein conformations - ANSWER1. binding of specific
molecules to channel proteins
2. changes in membrane potential
3. physically deforming the membrane
ligand-gated ion channel - ANSWERchanges shape in response to a signaling
molecule (ligand), allowing or blocking the flow of specific ions
voltage-gated ion channels - ANSWERChannels that open or close in response to a
change in the membrane potential.
mechanically gated ion channels - ANSWERopened or closed by deformation or
stretch of the plasma membrane
transporters - ANSWERintegral membrane proteins that mediate passage of
molecules through membrane
mediated transport - ANSWERmovement of molecules across membrane by binding
to protein transporter
factors that determine solute flux through mediated-transport system - ANSWER1.
solute concentration
2. affinity of transporters for solute
3. number of transporters in membrane
4. rate at which conformational change in transport protein occurs
facilitated diffusion - ANSWERthe movement of specific molecules across a cell
membrane through protein channels
high to low
active transport - ANSWEREnergy-requiring process that moves material across a
cell membrane against a concentration gradient
primary active transport - ANSWERdirect use of ATP
secondary active transport - ANSWERuse of an electrochemical gradient
Cotransport (symport) - ANSWERmovement of solute into the cell
