Cell Biology Membrane Transport and Cell Signaling

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133 Terms

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Membranes
act as a permeable shield; retain metabolic intermediates, release waste compounds
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What kinds of molecules can diffuse across the membrane
size and polarity matter, but you have to ask if it’s charged
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Free energy
a measure of the potential energy of a system; a function of enthalpy and entropy
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Entropy
a measure of the degree of disorder or randomness in a system; the greater the spots in the room, the greater the entropy
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enthalpy
total bond charges present in a chemical reaction
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If delta G is -
energetically favorable
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if delta G is +
not energetically favorable
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Gibb’s Law
all system change in such a way that free energy is minimized
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if delta G is -
the reaction will occur spontaneously
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if delta G is +
reaction will only occur with an input of energy
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if delta G is 0
the reaction is at equilibrium
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simple diffusion
does not use any energy to move across the membrane; movement down the concentration gradient
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will entropy increase or decrease in diffusion
increase in entropy due to more space
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will delta G increase or decrease with diffusion
delta G will decrease due to the increased entropy
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whether or not something diffuses is dependent on
it’s partition coefficient
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if you are moving something from low concentration to high concentration…
the number of available spaces does down
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if you are moving something form high to low concentration…
the number of available spaces goes up
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partition coefficient
the measure of a substance’s solubility in lipid
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in simple diffusion
rate is linear; partition coefficient is relevant
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in simple diffusion, if there is a higher partition coefficient
you have a steeper slope
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in simple diffusion, if you have a lower partition coefficient
you have a less steep slope
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in simple diffusion
there is no theoretical maximum
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what is the rate of simple diffusion dependent upon
concentration
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what is the rate like in transporter-mediated diffusion
greater than simple diffusion
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the partition coefficient in transporter-mediated diffusion
is irrelevant because it would be so low that you would need a transporter to move the molecule
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the max rate in transporter-mediated diffusion
is due to the limited number of transporters
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max rate
Vmax
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transporter-mediated diffusion is
transporter specific
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the rate of transporter mediated diffusion
is dependent on the affinity(Km) of the transporter for the transported molecule
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as actual affinity increases,
Km decreases
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what is the relationship between Km and affinity
reciprocal
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what is the rate in transporter-mediated diffusion dependent on
concentration
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for uriporters, we go
down the concentration gradient
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the function of uniporters depends on
the number of transporters, the affinity of transporters for substrate, the concentration outside of the cell
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in uniport function, what is the function of the partition coefficent(K)
K is irrelevant
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what happens to the shape of the curve as affinity increases in simple diffusion
simple diffusion will be a straight line
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what happens to the shape of the curve as affinity increases in transporter-mediated diffusion
the slope of the line can be affected by the partition coefficient
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the higher the partition coefficient
the higher the curve
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in simple diffusion, the higher rate of concentration means
the greater the rate of transport
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in transporter-mediate diffusion, the plateau
is due to the limited number of transporters
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active transport uses energy because
we are moving something against its concentration gradient, entropy is negative
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Why do ions need to use an ion channel
ions are really smal, but they are charged
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how do ion channels know what ions to move across the membrane
multipass transmembrane proteins have a selectivity loop
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where are ion channels placed within the membrane
within small pockets known as vestibules
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how specificity in ion channels determined
by the distance between oxygens within the vestibule
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within the vestibule
oxygens are free to move around
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how is gating within ion channels regulated
changed in membrane potential or ligand binding
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K+ leak channels
are always open even in an unstimulated or resting state
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what does it mean when the K+ leak channels are always open
this channel will always be moving ions form an area of high concentration to low concentration
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what are the three main sources of energy in active transport
light, ATP-drive pump, coupled transporter
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where is light used within active transport
a limited number of places
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ATP-driven pump
primary active transport; will use ATP as a source of energy
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within a p-type pump, are kinases used
no
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within a p-type pump, what is being phosphorylated
aspartic acid
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sarcoplasmi reticulum
when the ER contains a high amount of Ca2+
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the p-type pump is composed of
ten alpha helices
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in a p-type pump what will bind
calcium
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within the p-type pump, how many calciums will the binding site accommodate
two
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where does the ATP bind in the p-type pump
the nucleotide binding domain
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in the p-type pump, where will the phosphate move
to the aspartic acid
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what is the movement of the phosphate going to lead to
a conformational change
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within the p-type pump ADP is
converted back to ATP, but the P still remains
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within the p-type pump, calcium is..
released
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what happens to H+ in the p-type pump
2H+ binds
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what is the function of H+ and H2O
they stability the empty Ca2+ binding sites
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after the Ca2+ binding site is stabilized
P is released from its binding site
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under conditions when you don’t have an affinity change
passive transport will be used
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a lower concentration of K+ outside the cell and a higher concentration inside the cell is possible with the..
K+ leak channel because there is a mechanism that transports K+ back into the cell
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a higher concentration of Ca2+ outside the cell and a lower concentration of Ca2+ inside the cell is possible because…
as Ca2+ moves with its concentration gradient inside the cell there is a mechanism that transports it back outside the cell
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Sodium-Potassium ATPase
protein that will move sodium out of the cell and move potassium into cell
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within the Sodium-Potassium ATPase
for every three sodium molecules, two molecules of potassium will be pumped inside
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how is a gradient created that pulls water into the cell
cells contain a high concentration of solutes including negatively charged organic molecules that are confined inside the cell and their accompanying cations that are required for change balance
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how is the gradient pulling water into the cell counteracted
by an opposite osmotic gradient due to high concentration of inorganic ions in the extracellular fluid
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the Na+-K+pump helps maintain this balance by
pumping out Na+
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coupled transporters
facilitate the transport of one molecule to the energetically favorable
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Na+-Glucose symporter
an example of a coupled transporter
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Within the Na+-Glucose Symporter
Na+ and glucose binding are cooperative, transition to the occluded state only occurs when both Na+ and glucose are bound
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within the Na+-Glucose Symporter what does it mean to say that the binding sites for Na+ and glucose are “cooperative“
Na+ binding increases the affinity for glucose
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within the Na+-Glucose Symporter stochastic fluctuations caused by thermal energy
drive the transporter randomly
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Signal transduction
the process whereby a cell receives an extracellular signal and converts it to an intracellular signal that alters cell behavior
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effector proteins
metabolic enzymes, transcription regulatory proteins, cytoskeletal proteins
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How are effector proteins altered
A signaling molecule of some sort is going to engage a receptor on the plasma membrane, which will activate a series of events with intracellular signaling proteins
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what is the first messenger molecules
the extracellular signaling molecule
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What is the second messenger molecule
small intracellular molecules whose concentration changes in response to binding of an extracellular signal and functions in signal transduction
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Contact-dependent signaling
a signaling molecule is directly attached to the target cell via a membrane bound signaling molecule on the signaling cell and a receptor on the target cell
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paracrine system signaling
signaling molecules are released from a signaling cell, and the molecules find their way to the receptor adjacent cells
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synaptic signaling
combination of paracrine and contact-dependent signaling; involves neurons and synapses
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endocrine system
a signaling molecule is dumped into the bloodstream
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the response to a specific signaling molecule
is cell type dependent
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cross talk
intermediates in one transduction pathway can affect intermediates in another pathway
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when can the receptor be inside the cell
if the signaling molecule can cross the cell membrane if the signaling molecule is small and hydrophobic
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what moves the cell signal across the membrane
a carrier protein
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why are carrier proteins needed
since the signal molecules tend to be non polar, the molecule will aggregate before it can get to the receptor
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signaling molecules need to be
something that can alter protein function or gene expression and can be elevated under certain conditions
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how many domains do transcription factors have
two; DNA binding domain and activation/repressor domain
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what are the classes of surface receptors
ion-channel-coupled receptors, g-protein-coupled receptors, and enzyme-coupled receptors
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an ion-channel-coupled receptor
is both an ion channel and a receptor for a signaling molecule
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ion channel-coupled receptors interact with chemical signals by
transducing a chemical signal into an electrical signal by allowing an ion to move across the membrane
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small monomeric g-proteins
direct effects on effector molecules and relay signals from cell surface receptors
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large trimeric g-proteins
bind and are activated by cell surface receptors