Uni 1.3 - Membrane Proteins

Question 1

What type of molecules can pass directly through the membrane?

Answer 1

Non-polar molecules

Question 2

What are the two types of channels?

Answer 2

Gated and Ungated

Question 3

Give an example of an ungated channel

Answer 3

Aquaporin

Question 4

Describe Aquaporin and it’s function

Answer 4

Ungated channel that allows water to pass through the membrane

Question 5

What are the two types of gated channels?

Answer 5

Ligand and Voltage Gated

Question 6

What is required for a ligand gated channel?

Answer 6

Binding of a ligand

Question 7

Give an example of a ligand gated channel

Answer 7

A channel in the synpase, where a neurotransmitter binds to allow Na+ ions through

Question 8

What do voltage gated channels rely on to open?

Answer 8

A large enough change in the ion concentration across the membrane

Question 9

Describe how transporter proteins work

Answer 9

Change conformation to transport molecules across the membrane

Question 10

What are the two mechanisms that transporter proteins work with?

Answer 10

Facilitated

Active

Question 11

What is facilitated transport?

Answer 11

Passive process that does not require energy (but does require a conformational change if by a transporter)

Question 12

Give an example of a facilitated transporter protein and what it is used for

Answer 12

GLUT4 transporter in fat and muscle cells

Provides the route for facilitated diffusion of glucose across the cells

Question 13

What is coupled transport? Give an example

Answer 13

Coupled transport is where two substances are moved together

Glucose Symport

Question 14

What is the difference between a symport and an antiport?

Answer 14

Symport - both molecules move in the same direction

Antiport- both molecules move in opposite directions

Question 15

What does the glucose symport move?

Answer 15

Glucose and Na+

Question 16

Where can the glucose symport be found?

Answer 16

Cells lining the small intestine

Question 17

What is Signal Transduction?

Answer 17

A process triggered by the binding of a chemical signal to a receptor leading to a cellular response

Question 18

Where do hydrophobic signal bind?

Answer 18

Receptor proteins inside the cell

Question 19

What does the binding of a hydrophobic signal cause?

Answer 19

Activates/Inhibits the transcription of certain genes

Question 20

Give examples of responses that signal transduction can trigger

Answer 20

Changing the cell metabolism
Altering the uptake/secretion of molecules
Rearranging the cytoskeleton
Altering gene expression

Question 21

How are G proteins involved in signal transduction?

Answer 21

Involved in transmitting signals from outside the cell

Invovled in cascades, activated by binding GTP

Question 22

How many sodium ions are moved by the sodium potassium pump?

Answer 22

3 Na+ ions

Question 23

In what direction does the pump move sodium ions?

Answer 23

Out of the cell

Question 24

How many potassium ions are moved by the Na/K ATPase?

Answer 24

2 K+ ions

Question 25

In what direction does the pump move potassium ions?

Answer 25

Into the cell

Question 26

Describe the first conformation of the Sodium Potassium Pump

Answer 26

Binding sites exposed to the cytoplasm
High affinity for sodium ions
No ATP binded

Question 27

Describe the steps in the sodium potassium pump

Answer 27

Stage 1:
Ion binding sites exposed to cytoplasm
Protein has high affinity for sodium ions
3 Na+ ions bind
Stage 2:
ATP is hydrolysed by the protein forming ADP and Pi.
Pi binds to the protein, causing a confirmational change
Stage 3: In second confirmation, pump no longer has affinity for sodium so releases them. High affinity for potassium ions. 2 potassium ions bind
Stage 4: Dephosphorylation occurs and the pump loses the Pi
This causes another confirmational change, binding sites facing cytoplasm
Loses the K+ ions
Back to original confirmation

Question 28

Give three reasons why the movement of sodium and potassium ions is so important

Answer 28

Maintains an osmotic balance in animal cells
Generation of sodium ion gradient for glucose symport
Generation of sodium ion gradient in kidney tubules
Generation and Maintenance of ion gradients for resting potential in neurons

Question 29

How does the sodium potassium pump help maintain an osmotic balance in animal cells?

Answer 29

Moves three Na ions out and 2 K ions into the cell, lowers the overall ion concentration
increases the new water concentration

Question 30

How does the sodium potassium pump help the glucose symport?

Answer 30

Creates a sodium ion gradient from intenstine to lining cell

Enables the action of glucose symport to absorb sodium ions and glucose from the intestine

Question 31

What is the resting potential?

Answer 31

Imbalance in the electrical charge across a neuron membrane

Question 32

Where does the neurotransmitter bind?

Answer 32

Ligand gated Sodium Channel

Question 33

How is a nerve impulse generated?

Answer 33

Neurotransmitter binds to a receptor protein on a ligand gated sodium channel
Binding allows Na ions to diffuse into cell
If sufficent ion movement, voltage changes across the membrane
Causes neighbouring voltage gated Na+ channels to open
Triggers the next voltage gated channel and a wave of depolarization

Question 34

How is the resting potential restored?

Answer 34

When voltage reaches a critically high level, voltage gated Na+ channels close
Voltage K+ Channells open, so K+ ions diffuse out of neuron
Restoring the resting potential
K+ channels close when the resting potential is reached