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