Unit 1 - Membrane Structure and Transport

Carriers

Moves large, water soluble molecules across membrane

Channels

Moves small, water soluble ions across membrane

Diffusion

Random movement of molecules between regions with different concentration

Requirements of diffusion

Concentration gradient and brownian motion

Brownian Motion

Motions of molecules due to interactions between them

Simple Difussion

Molecule moves through cell membrane

Flux (J)

Number of molecules passing through a cross-sectional area in a period of time

Factors that affect diffusion rate

• Concentration of substance

• Membrane permeability

• SA

• MW

• Thickness

Facilitated Diffusion

Movement via channel/carrier protein (can be bidirectional)

Fick’s Law of Diffusion

[C]/distance

Properties of Ion Channels

• Conducts ions across membrane

• Recognize and select specific ions

• Open and closes from stimuli

Hetero-oligomers

Different protein subunits

Homo-oligomers

Same protein subunits

Monomeric

Single polypeptide forms its own subnits via motif

Where is the voltage sensor in voltage gated Na channels?

Alpha helix 4

Na Voltage Gated P Loops

Between alpha helix 5 and 6 forms the pore as the selective filter

Where is the inactivation gate in Na voltage gated channel?

Between domain 3 and 4

Ways Ion Channels can be blocked

• Change in a region

• General structure change

• Blocking/pluggin

How is selective passage achieved in ion channels?

Weak binding with transported ion, pore diameter and electrostatic interactions

Hydration Cloud

How H₂O molecules orient around ions

Ligand Gated Channels

Responds to a specific extracellular neurotransmitter

Signal Gated Channel

Responds to a specific intracellular molecule

Gigaseal

Discovered by Neher, which is a tight seal between cell and pipette with alot of resistance causing all ions to flow from channel to pipette

Charge of an ion

1.6 × 10^-19C

What does 1pA equal to?

10^-12A

What does 10^-12A equal to?

10^-12C/s

Inside Out Patch Clamp

Channel is ripped from cell to expose the inside to extracellular solution

Outside out patch clamp

Channel is ripped and reanneals to see how it reacts to varying extracellular solutions

Whole Cell Patch Clamp

Pipette breaks a hole to have access to the inside of the cell

Channelopathies

Channel Malfunctions

Hyperkalemic Periodic Paralysis

Mutations in voltage gated Na channel, causing inability to close inactivation gate and high K levels

Resting Membrane

-60 to -70mV

Nernst Equation

Simplified Nernst Equation