KA3 - Membrane Proteins

Question 1

The phospholipid bilayer acts as?

Answer 1

A barrier to ions and most uncharted polar molecules

Question 2

What can pass through the phospholipid bilayer?

Answer 2

Some small molecules such as oxygen and carbon dioxide

Question 3

What do specific transmembrane proteins act as?

Answer 3

Channels or transporters

Question 4

Specific transmembrane proteins act as channels or transporters. Why’s does this control?

Answer 4

Controls ion concentrations and concentration gradients

Question 5

To perform specialised functions what do different cell types have/do?

Answer 5

To perform specialised functions different cell types and different cell compartments have different channel and transporter proteins

Question 6

Passage of molecules through channel proteins is?

Answer 6

Passive

Eg. Aquaporin

Question 7

Some channel proteins are gated. What does this mean?

Answer 7

They change conformation to allow or prevent diffusion

Such as, sodium channels or potassium channels

Question 8

What can ‘gated’ channels be controlled by?

Answer 8

Signal molecules (ligand- gated channels) or changes in ion concentrations (voltage- gated channels)

Question 9

Why do transporter proteins change conformation?

Answer 9

To transport molecules across a membrane

Question 10

Transport can be facilitated.

Give an example of this

Answer 10

Glucose support

Active Na/KATPase

Question 11

What does conformational change in active transport require?

Answer 11

Energy from hydrolysis of ATP

Question 12

What do some cell surface receptor proteins convert?

Answer 12

An extracellular chemical signal to a specific intracellular response through a signal transduction pathway

Question 13

What may signal transduction result in?

Answer 13

The activation of an enzyme or G protein
A change in uptake or secretion of molecules, rearrangement if the cytoskeleton
Or activation of proteins that regulate gene transcription

Question 14

How does the sodium potassium pump transport ions?

Answer 14

Transports ions against a steep concentration gradient using energy directly from ATP

The transporter protein has high affinity for sodium ions inside the cell so binding occurs

Phosphorylation by ATP causes conformational change of the sodium potassium pump

Affinity for ions changes, sodium ions are released outside of the cell and potassium ions bind outside of the cell

Dephosphorylation occurs which causes conformational changes

Potassium ions are taken into the cell and the affinity returns to the start

Question 15

What does maintenance of ion gradients by Na/KATPase account for?

Answer 15

A significant part of basal metabolic rate (up to 25% in humans)

Question 16

Describe the functions of Na/KATPase

Answer 16

Maintaining the osmotic balance and animal cells

Generation of the ion gradient for glucose dumpiest in small intestines

Generation and long-term maintenance of ion gradient for resting potential in neurons

Generation of ion gradient in kidney tubules

Question 17

What is nerve transmission?

Answer 17

A wave of depolarisation of the resting potential of a neuron

Question 18

How can nerve transmission be stimulated?

Answer 18

When an appropriate signal molecule such as a neurotransmitter, triggers the opening of ligand-gated ion channels at a synapse

If sufficient ion movement occurs, then voltage-gated ions will open and the effect travels along the length of the nerve

Question 19

What happens once the wave of depolarisation has passed?

Answer 19

These channel proteins close and others open to allow the movement of ions in the opposite direction to restore the resting potential