M&R 2.1 - Role Of Membranes As Permeability Barriers

Question 1

What is the definition of passive transport?

Answer 1

The passage of a molecule through a membrane without any assistance

Question 2

What are the depending factors of passive transport? Describe the relationship between the factors and the rate

Answer 2

• Dependent on membrane permeability and concentration gradient
• The relationship is linear I.e. Increased rate of transport = increased concentration gradient

Question 3

How are transport processes important? Give 6 reasons

Answer 3

• Maintain ionic processes and composition
• Maintain intracellular pH
• Regulate cell volume
• Maintain concentration of metabolic fuels etc
• Remove waste products and toxic substances
• Generate an ion gradient

Question 4

How does a transporter pick up a substrate and transport it across the membrane?

Answer 4

‘Ping pong transport’

• Uses a gated pore
• Binding of the molecule causes a conformational change
• Substrate is released on the other side

Question 5

Give an example of a ligand gated ion channel

Answer 5

Nicotinic acetylcholine receptors

• Stimulation of receptor by nicotine causes release of acetylcholine

Question 6

What is an ion channel?

Answer 6

A pore that selective to specific ions

Question 7

What happens when ATP binds to ATP sensitive K+ channels? Why is this significant?

Answer 7

• Binding causes the channel to close
• Stops efflux of K+
• Significant when couple glucose metabolism to insulin release

Question 8

What is a voltage gated ion channel?

Answer 8

An ion channel that recognises electrical potentials across a membrane

A change in the electrical field causes the protein to move therefore opening to ions

Question 9

How do transport processes contribute to the control of transport of molecules in and out of the cell?

Answer 9

• Integration of specific proteins in the membrane

- Increases the permeability of what would be available from simple diffusion

Question 10

Describe active transport

Answer 10

Allows the transport of ions/molecules against an unfavourable concentration/electrical gradient using the direct or indirect hydrolysis of ATP

Question 11

Describe the energy changes when movement is dependent on a concentration gradient

Answer 11

• Passive = negative change in free energy therefore discharging gradient and releasing energy
• Active = positive change in free energy therefore charging gradient and using energy

Question 12

Describe the energy changes when movement is dependent on membrane potential

Answer 12

• Passive = negative change in free energy so moving from positive to negative
• Active = positive change in free energy so moving from negative to positive

Question 13

When would movement be membrane potential dependent rather than concentration gradient dependent?

Answer 13

When there is an equal distribution of concentrations on either side of the membrane

Question 14

What are the external and internal Na+ concentrations and which way is the gradient?

Answer 14

• 145mM outside, 12mM inside

- Electrical and chemical gradient is INWARDS

Question 15

What are the external and internal K+ concentrations and which way is the gradient?

Answer 15

• 4mM outside, 155mM inside

- Electrical and chemical gradient OUTWARDS

Question 16

What are the external and internal Cl- concentrations and which way is the gradient?

Answer 16

• 123mM outside, 4.2mM inside
• Concentration gradient INWARDS
• Electrical gradient OUTWARDS

Question 17

What are the external and internal Ca2+ concentrations and which way is the gradient?

Answer 17

• 1.5mM outside, 10-4mM inside

- Electrical and chemical gradient INWARDS

Question 18

Describe co-transport

Answer 18

More than one type of ion or molecule maybe transported on a membrane transporter per reaction cycle

Question 19

What are the two types of cotransporter? Describe them

Answer 19

• Symport = transport of 2 ions/molecules in one direction

- Antiport = transport of one substance inwards and one substance outwards in one cycle

Question 20

Which types of molecules are able to pass straight through a molecule and which types are unable to?

Answer 20

Can pass straight through:

• Hydrophobic molecules e.g. O2 and steroid hormones
• Small, uncharged and polar molecules e.g. H20, glycerol

Can’t pass straight through:

• Large, uncharged and polar molecules e.g. Glucose
• Ions e.g. H+, Na+