Lecture 2

Question 1

What is electrochemical gradient?

Answer 1

net flow of ions accross membrane.

Question 2

What is the resting membrane potential in - mV? how potassium and Na reacting to that number?

Answer 2

• The resting membrane potential is -70 mV which means neither potassium (-90 mV) or sodium (+65 mV) are at equilibrium.

Question 3

What is a diffusive driving force?

Answer 3

generated by the concentration difference

Question 4

What is an electrical driving force?

Answer 4

the force generated by a potential difference in an electrical field.

Question 5

What governs the specific ion movements across PM?

Answer 5

-The driving force and number of open channels.

Question 6

The chemical and electrical forces are complementary in the case of sodium because?

Answer 6

-Both the charge and concentration are higher extracellularly and lower inside the cell so it increases the potential of Na wanting to enter the cell.

Question 7

The chemical and electrical forces are offset incompletely in the case of Potassium because?

Answer 7

-Potassium is in a high concentration inside the cell so the chemical forces wants to take it out but the electrical forces offset that because it needs K+ to stay inside the cell.

Question 8

The chemical and electrical forces of Cl- are offset completely because?

Answer 8

The concentration of Cl- inside the cell is low so concentration wants more inside the cell but the cell is already negative so the electrical forces do not Cl- to go in. So the two forces offset each other.

Question 9

What are the uses of the Nernst equation?

Answer 9

-If you have the concentration gradient of an ion then you can calculate the electrical gradient.

Question 10

How is the driving force (Vm- Veq) is explained?

Answer 10

-The driving force is the difference between membrane potential and the equilibrium potential required. if the membrane potential for K+ is -90 and the cell resting potential is -70 then the difference is 20. 20 is the driving force and that is considered low driving force. On the other hand Sodium would have high driving force because its Veq = +60mV and since the Vm =-70 mV then the difference is 130 mV which is a large driving force.

Question 11

What is conductance? What are the two meanings of conductance?

Answer 11

• Opposite of resistance which means how easily the charges would go through.
• Conductance can mean for one channel or for the whole cell.

Question 12

What is a high conductance channel vs a low conductance channel?

Answer 12

High conductance channel will let more current through but low conductance channel will let less current through.

Question 13

What is shunting inhibition?

Answer 13

• Inhibitory Neurotransmitters such as GABA and glycine Open chloride channels but since the resting membrane potential is similar to the equilibrium potential of Cl- so
• The opening of Cl- channels do not change the voltage of the cell but it “Shunts” responsiveness to Na+ channels.

Question 14

What does the Goldman-Hodgkin-Katz equation explain?

Answer 14

-The permeability and equilibrium potential of each ion determines the membrane potential.

Question 15

Which one is faster in terms of Ion movements channels or carriers?

Answer 15

-Channels.

Question 16

What is gated diffusion?

Answer 16

-its dictated by voltage, ligand or mechanical force.

Question 17

What is selective diffusion?

Answer 17

Ions pass through channel based on size and charge.

Question 18

Whats the structure of the Na channel?

Answer 18

It has four domains and each has 6 Transmembrane segments that combine to form a barrel.
-It has an inactivation channel.

Question 19

Whats the structure of K channel?

Answer 19

Its made out of 6-TM peptide and its the combination of 4 of this peptide to form this channel.

• The potassium channel 6 TM peptide has the S4 region which has lots of positive amino acids and its referred to as the voltage sensor.
• S5 and S6 are known as the gate and between them, there is H5 which is the P loop and that determines which ion goes through.

Question 20

What is a Cyclic Nucleotide-gated channel?

Answer 20

• They’re part of the 6 TM channel family and also has 4 domains. it is activated by cAMP or cGMP.
• its involved in vision and olfaction

Question 21

What are TRP channels?

Answer 21

Also part of the 6 TM channel family and it varies in sensitivities from PH, Temperature, Menthol, Capsiacin and also involved in sweet, bitter and umami taste buds.

Question 22

What is an epithelial sodium channel? What is its structure?

Answer 22

• It is always open and it detects salty taste. the sodium from NaCl that goes through help detect the taste.
• These channels are also involved in salt excretion in the kidneys.

-Structure: made of 3 subunits (alpha, beta and gamma) and each subunit has 2 TM segment and a large Extracellular loop.

Question 23

What is the function of aquaporin? what is the structure and where is it prominent?

Answer 23

• Water can diffuse through the PM but these channels facilitate the movement of water.
• It also moves glycerol and urea but does not allow the passage of charged ions.

-The structure: 6 TM and 4 subunits and it’s also prominent in the kidneys.

Question 24

What are the ligand operated gates?

Answer 24

-They requiret the chemical binding of chemicals (mostly neurotransmitters) in ligand receptors.

Question 25

What are Ionotropic receptors? What excites these receptors and what inhibits them?

Answer 25

• They bind ligand and rapidly activate the channel.
• The channel itself is part of the receptor.

Excitation: Acetylcholine and Glutamate
Inhibition: GABA and glycine.

Question 26

What is a GPCR?

Answer 26

a G-Protein coupled receptor.

Question 27

What are the properties of GPCR? What are some examples?

Answer 27

• it has 7 transmembrane proteins.
• activates with a ligand but does not contain a channel.
• It Activates a G-Protein within the cell and starts a 2nd messenger cascade.
• Often regulates a channel and amplifies the response of a stimulus.

Examples:

• Sweet, bitter, umami taste receptors
• Neurotransmitter receptors
• Rhodopsin (Photoreceptors)
• Olfactory receptors.