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

Describe the structure of Aquaporin

Answer 5

Surface has some hydrophobic R groups(to allow it to be embedded in the membrane) but also some hydrophyllic R groups to help water molecules pass through the narrow parts of the pore

Question 6

What are the two types of gated channels?

Answer 6

Ligand and Voltage Gated

Question 7

What is required for a ligand gated channel?

Answer 7

Binding of a ligand

Question 8

Give an example of a ligand gated channel

Answer 8

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

Question 9

What do voltage gated channels rely on to open?

Answer 9

A large enough change in the ion concentration across the membrane

Question 10

Describe how transporter proteins work

Answer 10

Change conformation to transport molecules across the membrane

Question 11

What are the two mechanisms that transporter proteins work with?

Answer 11

Facilitated

Active

Question 12

What is facilitated transport?

Answer 12

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

Question 13

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

Answer 13

GLUT4 transporter in fat and muscle cells

Provides the route for facilitated diffusion of glucose across the cells

Question 14

What is coupled transport? Give an example

Answer 14

Coupled transport is where two substances are moved together

Glucose Symport

Question 15

What is the difference between a symport and an antiport?

Answer 15

Symport - both molecules move in the same direction

Antiport- both molecules move in opposite directions

Question 16

What does the glucose symport move?

Answer 16

Glucose and Na+

Question 17

Where can the glucose symport be found?

Answer 17

Cells lining the small intestine

Question 18

What is Signal Transduction?

Answer 18

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

Question 19

Where do hydrophobic signal bind?

Answer 19

Receptor proteins inside the cell

Question 20

What does the binding of a hydrophobic signal cause?

Answer 20

Activates/Inhibits the transcription of certain genes

Question 21

Give examples of responses that signal transduction can trigger

Answer 21

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

Question 22

How are G proteins involved in signal transduction?

Answer 22

Involved in transmitting signals from outside the cell

Invovled in cascades, activated by binding GTP

Question 23

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

Answer 23

3 Na+ ions

Question 24

In what direction does the pump move sodium ions?

Answer 24

Out of the cell

Question 25

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

Answer 25

2 K+ ions

Question 26

In what direction does the pump move potassium ions?

Answer 26

Into the cell

Question 27

Describe the first conformation of the Sodium Potassium Pump

Answer 27

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

Question 28

Describe the steps in the sodium potassium pump

Answer 28

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 29

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

Answer 29

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 30

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

Answer 30

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

Question 31

How does the sodium potassium pump help the glucose symport?

Answer 31

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 32

What is the resting potential?

Answer 32

Imbalance in the electrical charge across a neuron membrane

Question 33

Where does the neurotransmitter bind?

Answer 33

Ligand gated Sodium Channel

Question 34

How is a nerve impulse generated?

Answer 34

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 35

How is the resting potential restored?

Answer 35

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