Nernst equation (sept 9th)

Question 1

The Nernst Equation:

Answer 1

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
V=(RT/zF)2.305*log{C(o)/C(i)}

Question 2

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?

Answer 2

The voltage gradient and the concentration gradient.

Question 3

What happens when the voltage gradient and the and concentration gradient balance each other.

Answer 3

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)

Question 4

What is the free energy exchange per mol of solute moved by concentration gradient (aka random probability)?

Answer 4

RT*2.305log{C(o)/C(i)}

Question 5

What is the free energy exchange per mol of solute moved voltage

Answer 5

Vfz

Question 6

Explain the electrochemical gradient made in by potassium flow.

Answer 6

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.

Question 7

Current flows what way in biology:

Answer 7

Towards the most positive voltage.

Question 8

Electrochemical Driving Forces (EDFs) on Major Ions @ RMP

Answer 8

EDFs are a resting voltage minus the equilibrium potential for that ion
Na -89mv - 67mv
cl   -89mv--89mv
K   -89mv--89mv
Ca -89mv - 128mv

Question 9

Ligand-gated channels work how? What are two major types?

Answer 9

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.

Question 10

Mechanically gated channels work how?

Answer 10

They react to tension in the membrane, or changes in membrane shape in order to open or close.

Question 11

Voltage-gated channels

Answer 11

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.

Question 12

How does a selectivity filter work on an ion channel (note:channel not transporter).

Answer 12

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.

Question 13

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 _____.

Answer 13

Towards the pore
Away from the pore
Because Positive ions will be in the pore.

Question 14

Hydration spheres are what?

Answer 14

Collection of favorable water interactions around an ion.

Question 15

A voltage gated sodium channel (vgsc) have how many repeating domains, what are the components of each of these domains?

Answer 15

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.

Question 16

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.

Answer 16

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.

Question 17

Which two amino acids are used for the S4 voltage sensor?

Answer 17

Lysine and arginine (both positive).

Question 18

What is the inactivation gate?

Answer 18

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.

Question 19

Voltage-sensitive/gated ion channels have lateral portals, at least in bacteria. What is the pharmaceutical significance of these portals?

Answer 19

Lateral portals are often the route by which drugs that block the channel enter.

Question 20

Describe the inside-out, detached patch recording technique. These are patch clamp techniques.

Answer 20

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.

Question 21

What was concluded from patch clamp technique recordings.

Answer 21

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.

Question 22

What can the velocity of an action potential get up to? Where is the voltage headed towards? When will it generally stop?

Answer 22

100m/s
~67mv the E(Na+), equilibrium potential for sodium.
Generally only gets to about 0mv.

Question 23

The squid Loligo was used for what?

Answer 23

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.

Question 24

What did reduction of Na levels outside the axon do to action potentials?

Answer 24

It reduced the electrochemical driving force. The cell depolarized less and took longer to do so.

Question 25

Do action potentials have sweet sweet thresholds?

Answer 25

Oh ya man…