Oxygen toxicity and metabolism

Question 1

What is the Fenton reaction?

Answer 1

H2O2 + Fe2+ → Fe3+ + OH• + OH-

produces OH• - most potent free radical

Question 2

What is the Haber-weiss reaction?

Answer 2

O2- + H2O2 → O2 + H2O + OH•

produces OH• - most potent free radical

Question 3

How do free radicals cause cellular damage?

Answer 3

• Free radicals damage proteins, lipids, carbohydrates and nuclei acids
• They damage the cell membranes of the cell, nucleus, mitochondria and endoplasmic reticulms
• This increases the permeability, which leads to an influx of calcium, water and sodium

Question 4

What is a respiratory burst?

Answer 4

• Respiratory burst is the immune systems defence against bacteria
• Reactive Oxygen Species are released during phagocytosis
• Superoxide O2•- is released, this generates other reactive oxygen species - eg HOCl and OH-
• these damages bacterial cell membranes
• lasts 30-60 mins

NADPH Catalyses oxygen to super oxide O2•- this leads to H2O2.

Fenton reaction catalyses H2O2 with Fe (2+ to 3+0) to produce OH-
myeloperoxidase catalyses H2O2 plus Cl- = HOCl

Question 5

What diseases are associated with free radicals?

Answer 5

• Atherosclerosis
• Diabetes
• Parkinson’s
• Ageing

Question 6

What is the hydroxylradical?

Answer 6

OH•
Most potent of reactive oxygen species
lipid soluble
it initiates chain receptors that form lipid peroxidase and organic radicals

Question 7

What super oxide?

Answer 7

O2•-
produced by ETC (electron leakage)
generates radicals locally

Question 8

What is hydrogen peroxide?

Answer 8

Hydrogen peroxide generates free radicals with transition metals H2O2 (eg fenton reaction)
It is lipid soluble

Question 9

How are organic radicals produced?

Answer 9

R•

Organic radicals are produced by OH• action

Question 10

How are organic peroxides produced?

Answer 10

Organic peroxides are produced by lipid degradation

Question 11

How is hyperchlorous acid produced?

Answer 11

hyperchlorous acid HOCl is produced in the respiratory burst of bacteria (it is in household bleach)

Question 12

Which free radicals does oxygen produce?

Answer 12

• O2•- superoxide
• H2O2 hydrogen peroxide
• OH• hydroxyl radical

Question 13

What defences does the body have against free radicals?

Answer 13

-Enzymes
-Antioxidants vitamins (ACE)
vitamin E, beta-carotene (vit A), and vitamin C.
-Cell compartmentalisation
-Repair

Question 14

What enzymes defend against free radicals?

Answer 14

superoxide dismutase - turns (O2−) radical into either molecular oxygen (O2) or hydrogen peroxide H2O2

catalase- catalyzes the decomposition of hydrogen peroxide into water and oxygen

glutathione - when glutathione is reduced it converts H2O2 to water

peroxidase - peroxide (H2O2) into Hydrochloric Acid (HOCl)

Question 15

What is Beta-carotene? What foods have a high source?

Answer 15

Beta-carotene is a precursor to vitamin A (retinol) and is present in liver, egg yolk, milk, butter, spinach, carrots, squash, broccoli, yams, tomato, cantaloupe, peaches, and grains. Because beta-carotene is converted to vitamin A by the body there is no set requirement

Question 16

What is vitamin E? What foods have a high source?

Answer 16

Vitamin E A fat soluble vitamin present in nuts, seeds, vegetable and fish oils, whole grains (esp. wheat germ), fortified cereals, and apricots.
(RDA) is 15 IU per day for men and 12 IU per day for women.

Question 17

What is Vitamin C? What foods have a high source?

Answer 17

Vitamin C : Ascorbic acid is a water soluble vitamin present in citrus fruits and juices, green peppers, cabbage, spinach, broccoli, kale, cantaloupe, kiwi, and strawberries. T
RDA is 60 mg per day. Intake above 2000 mg may be associated with adverse side effects in some individuals.

Question 18

What does NADPH oxidase catalyse?

Answer 18

NADPH Catalyses oxygen to super oxide O2•-

Question 19

What does myeloperoxidase catalyse?

Answer 19

myeloperoxidase catalyses H2O2 plus Cl- = HOCl which is used in bacterium respiratory burst