ELM 5 - Electrochemical Gradients

What happens regarding entropy in simple diffusion?

Entropy disorder increased: The second law of thermodynamics

What is simple diffusion?

Molecules spontaneously move from high areas of concentration to low areas of concentration

What happens when there’s a whole in the membrane (gradient and diffusion)?

Ions flow until concentrations equal on both sides

Eqm set up

Why do ions spread out?

Molecules in liquid are in constant motion due to thermal agitation

What is the average water molecule radius?

2.8A

What did Fick show?

number of molecules (N) moving across an interface is proportional to:

• Area of interface (A)

• The concentration gradient

What did Einstein say about diffusion?

• Diffusion due to random walk of molecules

• Distance of molecule from starting point after given time depends on dimension molecules are in

Give examples of 1D, 2D and 3D in regards to diffusion

1D diffusion → movement along DNA
2D diffusion → movement in a membrane

3D diffusion → movement in a liquid

Which dimension will a molecule be in if it travels furthest?

3D

Why will a molecule travel faster in a 3D dimension?

Because chances of bumping into each other are low

How do catalysts work?

Provide surface allowing molecules to bump into one another

Why do signalling molecules have more chance of interacting on a membrane?

Because they’re 2D

In what circumstance will signalling molecules have longer ranges?

If they’re not bound to membranes

What is electrophoretic movement?

Ion movement under the influence of an electric field

What influence does electrophoretic movement have on ion diffusion?

Will add or subtract from diffusion

What is the sum of total gradient?

Gradient caused by diffusion - Gradient caused by electrophoretic movement

What is the direction of ion movement determined by?

Electrochemical gradient (in or out of cell)

What is the rate of ion movement across membrane dependent on?

1. Size of electrochemical gradient

2. Nature of the ion

3. Number of open ion channels

4. The properties of the ion channel

What is current?

• Flow of ions

• Number of ions flowing per second

What is voltage?

• Potential difference

What is resistance?

• Related to width of path

• Low resistance = wide path

What is Ohm’s law

Current (I) = Volts (V) / Resistance (R)

What version of Ohm’s law do electrophysiologists use?

Current (I) = Volts (V) X Conductance

Conductance = 1/R

What concentration gradient will a high, strongly negative electrochemical gradient give?

• High concentration gradeitn

How does the effect of nature of ion impact ion movement? Give examples Na+ and Cl-

• Positive/ negative ions

• Number of charges on ion

Sodium ions - electrochemical gradient high

Chloride ions - concentration gradient high but electrical gradient in wrong direction - electrical gradient low

How can properties of ion channel influence rate of diffuion?

Selectivity and permeabiltity (structure )

Akin to resistance