Oxygen Metabolism

Question 1

What does ROS stand for?

Answer 1

Reactive oxygen species

Question 2

How would you chemically describe ROS?

Answer 2

Highly reactive oxygen containing free radicals

Question 3

Which radical is the most potent ROS?

Answer 3

Hydroxyl radical

Question 4

Name some exogenous sources or ROS.

Answer 4

UV radiation, tobacco, drugs

Question 5

Name some endogenous sources or ROS.

Answer 5

NADPH, electron transport chain

Question 6

How is oxygen converted to an ROS?

Answer 6

1. Oxygen is reduced by an electron to form superoxide
2. Superoxide is reduced further to hydrogen peroxide
3. Hydrogen peroxide is reduced further to form hydroxyl radical which is later reduced to water

Question 7

Which reaction catalyses the formation of a hydroxyl radical from hydrogen peroxide?

Answer 7

Fenton reaction

Question 8

Give the Fenton reaction

Answer 8

H2O2 + Fe2+ > Fe3+ + OH- + OH•

Question 9

Which reaction produces the hydroxyl radical from the superoxide?

Answer 9

Haber-Weiss reaction

Question 10

Give the Haber-Weiss reaction

Answer 10

O2•– + H2O2 + H+ > O2 + OH- + OH•

Question 11

The Fenton reaction and the Haber-Weiss reaction can be combined to forma series of 4 reactions - the Haber-Weiss Cycle. Write this out.

Answer 11

1. Fe2+ + H2O2 > Fe3+ + OH- + OH• [Fenton reaction]
2. OH• + H2O2 > H2O + O2•– + H+
3. O2•– + H+ + H2O2 > O2 + OH• + H2O [Haber-weiss reaction]
4. Fe2+ + OH• + H+ > Fe3+ + H2O

Question 12

Are hydroxyl radicals lipid soluble?

Answer 12

Yes

Question 13

Which molecules do free radicals damage?

Answer 13

Proteins, lipids, carbohydrates and nucleic acids

Question 14

Which cell organelles membranes do free radicals damage? What is the effect of this?

Answer 14

Nucleus, mitochondria, ER. Results in increased permeability of the membrane resulting in an influx of calcium, sodium and water.

Question 15

Name the immune defence against bacteria that involves the sudden release of ROS.

Answer 15

Respiratory burst

Question 16

Which cells release a respiratory burst?

Answer 16

Neutrophils, macrophages, monocytes

Question 17

Which compound is produced by neutrophils to damage bacterial cell membranes? It combines H2O2 with Cl-.

Answer 17

Hypochlorite

Question 18

The absence of which enzyme prevents the formation of ROS?

Answer 18

NADPH oxidase

Question 19

What are the consequences of no ROS formation?

Answer 19

Build of pathogens in phagocytes. They can engulf not kill them. Leads to severe skin infections.

Question 20

What is cellular compartmentalisation?

Answer 20

Respiratory burst that takes place in phagosomes so harmful chemicals aren’t released and damage healthy tissue.

Question 21

Name some key antioxidant enzymes.

Answer 21

Superoxide dismutase
Catalase
Glutathione peroxidase

Question 22

What is the function of catalase?

Answer 22

Catalyses hydrogen peroxide to water + O2. Protects white blood cells from own respiratory burst.

Question 23

What is the function of glutathione peroxidase?

Answer 23

Catalyses reduction of H2O2 to water + disulphide

Question 24

Name some key antioxidant vitamins.

Answer 24

Vitamin E and C

Question 25

What does vitamin E do?

Answer 25

Protects against lipid peroxidation. Terminates free radical propagation.

Question 26

What does vitamin C do?

Answer 26

Reacts with superoxide & hydroxyl radical, offers protection