Unit 1 - section 3

Question 1

Name 2 small molecules that can diffuse directly across the phospholipid bilayer

Answer 1

Oxygen

Carbon dioxide

Question 2

How does the bilayer act as a barrier to most other ions and molecules?

Answer 2

Molecules that are too large or too polar cannot diffuse directly across the phospholipid bilayer so require to be transported

Question 3

What is the function of channel proteins?

Answer 3

Allow passive transport down concentration gradients

Question 4

What is the function of transporter proteins?

Answer 4

Actively moves molecules across the membrane against concentration gradient

Question 5

What is the function of receptor proteins?

Answer 5

Receive signals and bring about responses

Question 6

Describe the role of membrane proteins in specialisation

Answer 6

Cell specialisation allows cells to perform specialised functions as different cell types and compartments must contain different channel and transporter proteins

Question 7

What is the membrane protein involved in the passive transport of water?

Answer 7

Aquaporin 2

Question 8

Name 2 types of gated channels

Answer 8

Ligand-gated channels

Voltage-gated channels

Question 9

Describe the operation of ligand-gated channels

Answer 9

Open and close following the binding of a ligand

Question 10

Describe the function of voltage-gated channels

Answer 10

Respond to changes in ion concentration

Question 11

Describe facilitated transport stating the energy requirement

Answer 11

Passive process so does not require energy. Unlike passive transport it involves a conformational change in the protein

Question 12

Describe active transport stating the energy requirement

Answer 12

Requires energy to bring about the necessary conformational change. Energy required comes from hydrolysis of ATP

Question 13

What is an example of an active transport protein?

Answer 13

Sodium potassium pump

Question 14

Define intracellular and extracellular

Answer 14

Intracellular means inside the cell

Extracellular means outside the cell

Question 15

What is the type of membrane proteins that bind to signal molecules?

Answer 15

Receptor proteins

Question 16

What is the type of pathway that is activated when a signal molecule is received?

Answer 16

A signal transduction pathway

Question 17

What are 4 potential responses of a cell to a signal molecule?

Answer 17

Activation of special enzymes or G-proteins
Changes in molecule uptake or release
Rearrangement of cytoskeleton
Activation of proteins that regulate gene expression

Question 18

What is the sodium-potassium pump also know as?

Answer 18

Na/KATPase

Question 19

Which way do ions go through the sodium-potassium pump?

Answer 19

Pumped against a steep concentration gradient

Question 20

Is energy required for the sodium-potassium pump?

Answer 20

Significant energy is required

Question 21

Describe the sodium-potassium pump’s affinity for sodium and potassium

Answer 21

Has a high affinity for the sodium ions inside the cell. Three sodium ions would bind to the pump. This would allow an ATP to bind to the pump changing its shape, causing it to release the sodium ions outside the cell. This causes a conformational change to the pump allowing two potassium ions to bind. This causes a conformational change to the pump releasing the potassium ions inside the cell. This process then repeats.

Question 22

When do phosphorylation and dephosphorylation occur in the sodium-potassium pump?

Answer 22

Phosphorylation - phosphate group binds to pump

Dephosphorylation - phosphate group is released

Question 23

What causes conformational changes to the sodium-potassium pump?

Answer 23

When the ligand binds to the pump

This allows the sodium be potassium ions to be pumped across the membrane

Question 24

What are 4 functions of the sodium potassium pump?

Answer 24

Maintenance of osmotic balance in animal cells
Generation of the ion gradient for glucose symport in the small intestine
Generation and long term maintenance of ion gradient for resting potential in neurons
Generation of ion gradient in kidney tube

Question 25

Why is the sodium-potassium pump so important in mammalian metabolism?

Answer 25

The generation of ion gradients by the pump accounts to a significant part of basal metabolic rate in mammals (25% in humans)

Question 26

What does depolarisation mean?

Answer 26

When a neuron becomes more positive and less negative

Question 27

What is nerve transmission?

Answer 27

The passing of a signal from one neuron to the next caused be a wave of depolarisation along a neuron

Question 28

What is resting potential?

Answer 28

The difference in voltage across the membrane when there is no signal

Question 29

What are the stages in the transmission of a nerve impulse?

Answer 29

Resting potential of the membrane is stable and slightly negative inside the neuron
Neurotransmitter binds to ligand gated channel
Ligand gated channels open and sodium ions enter the neuron
Neuron becomes less negative
If threshold is reached the voltage changes and the voltage gated ion channels open
Sodium ions flood into the neuron
Increase in sodium ions cause a wave of depolarisation through the neuron

Question 30

Describe phosphorylation of the sodium potassium pump?

Answer 30

Pump has high affinity for sodium ions inside the cell before binding
Phosphorylation by ATP causes conformational change to pump reducing affinity for sodium ions and releasing them outside the cell. Now high affinity for potassium ions outside the cell
Dephosphorylation occurs causing conformational change and releasing potassium ions inside the cell