7) Unit 1 - Movement of Molecules Across the Membrane

Question 1

Name the 3 major roles of the membrane

Answer 1

1) Movement of molecules across the membrane
2) Transmission of extracellular signals (Signal Transduction)
3) detecting and amplifying stimuli (Photoreceptor and Protein systems)

Question 2

What types of molecules can pass readily through the membrane and give an example

Answer 2

Hydrophobic molecules

E.g thyroxine

Question 3

What types of molecules does the membrane act as a barrier towards

Answer 3

• charged ions
• uncharged polar molecules (with exception of H2O, urea, glycerol)
• large molecules

Question 4

What is the function of transmembrane proteins

Answer 4

To facilitate the transport of molecules that can’t pass readily through the membrane

Question 5

List the two types of transmembrane proteins

Answer 5

Channels and transporters

Question 6

Describe what a channel protein is, with reference to gated channels

Answer 6

CHANNELS:

• allow the movement of molecules across the membrane without energy (passive)
• channels can be ligand gated or voltage gated.

Ligand gated:
Are controlled by the joining of a ligand, which causes conformational change of the channel

Voltage gated:
Are controlled by changed in ion concentrations

Question 7

Describe what a transporter protein is, with reference to facilitated and active transport

Answer 7

TRANSPORTERS

• transporter proteins change conformation to transport molecules across a membrane
• This can happen in two ways, facilitated or active transport

Facilitated:
Do not require energy to bring about the conformational change of the transporter protein

Active:
•Requires energy to bring about the conformational change of the transporter protein
•hydrolysis of ATP can provide energy for this process

Question 8

Give an example of a molecule that uses facilitated transport

Answer 8

Glucose

Question 9

Give an example of an transmembrane protein that is an active transporter

Answer 9

Sodium potassium pump

Question 10

What is the benefit of channels and transporters

Answer 10

Allows the control of ion concentrations and concentration gradients

Question 11

Give an example of a channel protein

Answer 11

Aquaporin channel, for the transport of water