INTRODUCTION

Question 1

What is the function of the cell membrane?

Answer 1

To divide intracellular fluid and extracellular fluid compartments.

Question 2

What are the components of the membrane by % weight?

Answer 2

Lipids - 42% Proteins - 55% Carbohydrates - 3%

Question 3

What are the main ionic components of all fluids in the body?

Answer 3

Sodium ions Potassium ions Calcium ions Carbonate ions Chloride ions Phosphate ions Proteins

Question 4

What is the concentration of potassium ions in the plasma, in relation to the intracellular fluid?

Answer 4

There is a low concentration of potassium ions in plasma compared to ICF.

Question 5

What is the concentration of sodium ions in the plasma, in relation to the intracellular fluid?

Answer 5

There is a high concentration of sodium ions in the plasma compared to ICF.

Question 6

What is the concentration of calcium ions in the plasma, in relation to the intracellular fluid?

Answer 6

There is a high concentration of calcium ions in the plasma compared to ICF.

Question 7

What is the concentration of carbonate ions in the plasma, in relation to the intracellular fluid?

Answer 7

There is a slightly higher concentration of carbonate ions in the plasma compared to the ICF.

Question 8

What is the concentration of chloride ions in the plasma, in relation to the intracellular fluid?

Answer 8

There is a a lot high concetration of chloride ions in the plasma compared to the ICF.

Question 9

What is the concentration of phosphate ions in the plasma, in relation to the intracellular fluid?

Answer 9

There is a low concentration of phosphate ions in the plasma compared to the ICF.

Question 10

What is the concentration of protein in the plasma, in relation to the intracellular fluid?

Answer 10

There is some protein in the plasma but there is a lot more protein in the ICF.

Question 11

What underpins physiological processes?

Answer 11

Transport across cell membranes.

Question 12

How do lipid soluble molecules such as oxygen and carbon dioxide get transported across the membrane?

Answer 12

Diffusion

Question 13

How do small molecules and ions get transported across the cell membane?

Answer 13

By transport proteins

Question 14

How do large molecules get transported across the membrane?

Answer 14

By endocytosis

Question 15

What types of transport protein are there?

Answer 15

Ion Channels Carriers Pumps (ATPases)

Question 16

What categories can carriers be classified into?

Answer 16

Uniporter Symporter Antiporter

Question 17

Which of the transport proteins are passive?

Answer 17

Ion channels and carriers

Question 18

Which of the transport proteins are active?

Answer 18

Pumps

Question 19

When does active transport occur?

Answer 19

In the absence of or against an electorchemical gradient

Question 20

What kind of turnover does active transport have?

Answer 20

<100 per second

Question 21

What is another way to classify ion channels?

Answer 21

By molecular family

Question 22

How do carriers go about transport?

Answer 22

By facilitated diffusion. A molecule will bind, there will be a conformational change in which allows the molecule to be released on the other side of the membrane. This is a passive process.

Question 23

What are the features of carriers?

Answer 23

Turnover high at 10^2-10^3 per second Highly selective Saturable

Question 24

What are the features of ion channels?

Answer 24

They have a high turnover of 10⁶-10⁸

They are passive

They are selective

They are gated

Question 25

What does electrogenic transport do?

Answer 25

Changes membrane potential.

Question 26

What is an example of a transporter that is electogenic?

Answer 26

Sodium/Potassium ATPase exchanges 3 sodium ions out of the cell and 1 potassium ion out of the cell.

Question 27

What is the structure of the Sodium Potassium ATPase?

Answer 27

It is a ubiquitous tetramer 2 alpha subunits and 2 beta subunits.

Question 28

What is the the Patch Clamp technique used for?

Answer 28

It is a method that can directly measure the function of ion channels.

Question 29

What is the Cell Attached Method?

Answer 29

It is one method of Patch Clamp Technique. A small pipette (with a tip 1x10^-6m) with salt solution and an electrode. The membrane forms a high resistance seal to the pipette tip. Electrical activity measured with respect to a reference.

Question 30

Another method of the Patch Clamp exists. If we rupture the membrane, the solution fills the cell and we can measure all the channels in the cell by measuring the currents at different potentials. What is this technique called?

Answer 30

Whole Cell Method

Question 31

How can you calculate the total current carried by a population of cells?

Answer 31

I= N.P₀.g (V_m-E_i) Where: I= total current carried by a population of cells N = number of channels P₀= open probability g = single channel conductance V_m= membrane potential E_i = equilibrium potential of an ion

Question 32

What is the structure of a bacterial K⁺ (K_csA) channel and how do we know?

Answer 32

The structre was found by visualising protein crystals using X ray. The most basic channel upon which many other ion channels have evolutionarily evolved. Two transmembrane spanning domains (s5 + s6). P loop to form a pore