Membranes as Permeability Barriers

Question 1

What is a semi-permeable membrane?

Answer 1

A layer through which only allowed substances can pass

Question 2

Name 2 molecules that move easily and 2 that have difficulty permeating through the lipid bilayer

Answer 2

Easy - respiratory gases, water, urea

Hard - glucose, sucrose, ions

Question 3

What is a permeability co-efficient?

Answer 3

Ability of a molecule to pass through a membrane

Question 4

What is passive transport dependent on?

Answer 4

• Permeability

- Concentration gradient

Question 5

Name 3 roles of membrane transport processes

Answer 5

• Maintenance of ionic composition
• Maintenance of intracellular pH
• Cell volume regulation
• Concentration of metabolic fuels and building blocks
• Extrusion of waste products
• Generation of ion gradients

Question 6

Which kind of membrane transport exhibits conformational change?

Answer 6

Gated pore channel

Question 7

Name the 4 types of facilitated diffusion via ion channels

Answer 7

Gated pore
Ligand-gated - binding opens channel
Ligand-gated - binding closes channel
Voltage-gated

Question 8

How does a voltage-gated ion channel work? Give an example

Answer 8

• Contains Voltage sensor
• Acts on the membrane potential
• Na+ channel

Question 9

What is the difference between active and passive transport?

Answer 9

Active - requires energy to create a gradient

Passive - concentration gradient drives direction of transport

Question 10

Name the 2 types of passive diffusion and 1 type of active transport

Answer 10

Passive - simple diffusion, facilitated diffusion

Active - transport against an unfavourable concentration/electrical gradient

Question 11

Which 2 ions are most prevalent outside cells and what are their concentrations?

Answer 11

Na+ - 145mM

Cl- - 123mM

Question 12

What are the extracellular concentrations of Ca2+ and K+?

Answer 12

Ca2+ - 1.5mM

K+ - 4mM

Question 13

Name 3 types of plasma membrane ion transporters

Answer 13

• PMCA - Plasma membrane Ca2+ ATPase
• ATP Synthetase
• Na+ Pump
• NHE - sodium H+ exchanger
• SGLT - sodium glucose transporter

Question 14

What is the action of a PMCA?

Answer 14

• Primary active transporter
• Powered by ATP hydrolysis
• Energy used to move calcium out of the cell
• High affinity and low capacity

Question 15

What is the action of ATP Synthetase in ATP synthesis and where does it occur?

Answer 15

• Reverse active transport
• Drives ATP synthesis and is reliant on H+ gradient
• Reversible
• Occurs in mitochondria

Question 16

Describe the action of a Na+ pump and what type of transport does it use?

Answer 16

• Active transport
• 3 Na+ ions expelled for every 2 K+ ions in
• Creates ion gradients

Question 17

What does a sodium/H+ exchanger do?

Answer 17

Creates a sodium gradient to enable extrusion of acid

Question 18

What is a uniport transport mechanism?

Answer 18

Movement of a single ion in one direction through the membrane

Question 19

What are the 2 types of co-transporter mechanisms and what do they mean in terms of ion movement?

Answer 19

Symport - Movement of two ions through a membrane in one direction
Antiport - Movement of two ions through a membrane in different directions

Question 20

Give 2 examples of co-transporter ion channels and what is their effect?

Answer 20

Na+ pump - Maintains cellular concentration of Na+ and K+
NCX - Inward flow of Na+ pushes Ca2+ out up a concentration gradient
NHX - Inward of flow of Na+ leads to alkalinisation by removing H+

Question 21

How do deficient ion channels contribute to Cystic Fibrosis?

Answer 21

• Defective CFTR gene inhibits Cl- transport out of the cell
• Osmotic pull for water connected with Cl-
• Less water to dilute mucous

Question 22

How does PKA contribute to Cholera?

Answer 22

• PKA activated by Gs
• PKA increases Cl- flow out of the cell
• Water follows Cl- out of the cell causing diarrhoea