Flashcards in Nernst equation (sept 9th) Deck (25):
The Nernst Equation:
V is the equilibrium potential, R is the gas constant 8.3, T is the temp in Kelvin z is the charge of the ion, F is faraday's constant ~10x10^5, C(o) is concentration outside, C(i) is the concentration inside
The flow of any inorganic ion through a membrane channel is driven by the electrochemical gradient for that ion. Which two things influence electrochemical gradient for an ion type?
The voltage gradient and the concentration gradient.
What happens when the voltage gradient and the and concentration gradient balance each other.
The net flow of ions is zero (note the word net, it matters). The voltage gradient at which this occurs is called the equilibrium potential (V, from nernst's equation)
What is the free energy exchange per mol of solute moved by concentration gradient (aka random probability)?
What is the free energy exchange per mol of solute moved voltage
Explain the electrochemical gradient made in by potassium flow.
K is concentrated inside the cell. It's movement outside of the cell through channels causes a loss of positive charge within the cell, and develops a voltage, with a negative charge in the cell and K flowing inward to try to relieve this loss at the same rate it is flowing outward due to the build up of a concentration gradient.
Current flows what way in biology:
Towards the most positive voltage.
Electrochemical Driving Forces (EDFs) on Major Ions @ RMP
EDFs are a resting voltage minus the equilibrium potential for that ion
Na -89mv - 67mv
Ca -89mv - 128mv
Ligand-gated channels work how? What are two major types?
Ligand binds and makes a conformational change. This change opens the channel. Aa channel can be orientated to except ligands from extracellular space or from the intracellular space.
Mechanically gated channels work how?
They react to tension in the membrane, or changes in membrane shape in order to open or close.
Are channels which will have positive amino acids (possible negative too) coating one side, apparently, the extracellular. In this example when a positive charged ion grows in frequency in the cell, and when negatives appear outside it will pull the channel open.
How does a selectivity filter work on an ion channel (note:channel not transporter).
All ions have a sphere of hydration. The selectivity filter is a series of ketones placed so as to be perfectly positioned to take over the favorable H-bond interactions performed by the water, but the placement is only the correct size to bond well with one ion type.
The half alpha helices which form the aqua-pore are polar, with a negative ______ the pore and a positive _____ the pore. This makes sense because _____.
Towards the pore
Away from the pore
Because Positive ions will be in the pore.
Hydration spheres are what?
Collection of favorable water interactions around an ion.
A voltage gated sodium channel (vgsc) have how many repeating domains, what are the components of each of these domains?
4 repeating domains. Each composed of a 4 alpha helices which act as a voltage sensor, S4 segment (one of these helices has periodic + charge), and two alpha helices that will act as part of the selectivity filter.
The four repeating domains of the voltage gated ion channel are called what, and interact with how many other proteins? Predominately intracellular or extracellular? Descbribe them.
they are the alpha portion, they interact with a beta 1 and 2 proteins. which are anchored in the membrane but are predominantly extracellular beta sheets.
Which two amino acids are used for the S4 voltage sensor?
Lysine and arginine (both positive).
What is the inactivation gate?
In voltage gated sodium ion channels this gate is what stops the potential from backing up. It is a part of the structure that will swing inwards to close it after a few milliseconds.
Voltage-sensitive/gated ion channels have lateral portals, at least in bacteria. What is the pharmaceutical significance of these portals?
Lateral portals are often the route by which drugs that block the channel enter.
Describe the inside-out, detached patch recording technique. These are patch clamp techniques.
A glass micropipette, 1 um thick, with gentle suction grabs a fragment of the membrane. This piece of the membrane may contain only a single ion channel, and the properties of this channel can be studied.
What was concluded from patch clamp technique recordings.
That while the duration that a voltage gated channels stay open varies, some even opening and closing, the voltage never goes beyond a certain voltage.
What can the velocity of an action potential get up to? Where is the voltage headed towards? When will it generally stop?
~67mv the E(Na+), equilibrium potential for sodium.
Generally only gets to about 0mv.
The squid Loligo was used for what?
It had an axon, 1 mm in diameter. This allowed scientists to 'roll' out the fluid inside and examine its composition. It also aloud for new fluids of known composition to be placed inside as well as electrodes in order to accurately measure voltage and observe the conditions of an action potential.
What did reduction of Na levels outside the axon do to action potentials?
It reduced the electrochemical driving force. The cell depolarized less and took longer to do so.