Lecture 7

Question 1

What is a free radical

Answer 1

A molecule with an unpaired electron

Question 2

Name 3 substances that may form ROS (reactive oxygen species)

Answer 2

smog, cigarette smoke, immune response

Question 3

Name two types of damage free radicals can form

Answer 3

DNA damage (eg nucleus, mitochondria)
Damage to lipids (oxidation, cell membranes)
Protein structure (amino acids,  RBC)

Question 4

What is an antioxidant

Answer 4

a substance that stops damaging effects of free radicals

Question 5

name 5 antioxidant nutrients

Answer 5

Vitamins A, C, E, CoQ10, selenium

Question 6

What are the 3 main endogenous antioxidants?

Answer 6

glutathione, CoQ10, super oxide dismutase, alpha-lipoic acid

Question 7

Name 3 exogenous antioxidants

Answer 7

Vits A, C, E, lipoic acid

Question 8

Which nutrients effectively ‘recycle’ each other?

Answer 8

ascorbate regenerates vitamin E

Question 9

What are 5 types of reactive species?

Answer 9

• superoxide radical
• hydrogen peroxide
• hydroxyl radical
• peroxyl
• carbon centred radicals

Question 10

How are oxygen centred radicals generated?

Answer 10

by oxygen reacting with different compounds (eg catcholamines (epinpehrines, norepinephrine, dopamine), or folate)

• the Electron transport chain produces them
• cytochrome P450
• activated blood cells during phaocytosis

Question 11

Functions of antioxidants

Answer 11

• prevent breakdown of polyunsaturated lipids in cell membranes
• donate electrons to electron seeking compounds (preventing cell damage)
• stop oxidation but do not donate electrons
• reduce LDL oxidation

Question 12

Which enzyme produces hydrogen peroxide while removing superoxide radicals?

Answer 12

superoxide dismutase

Question 13

Which nutrient may also produce hydrogen peroxide while removing SOD radicals?

Answer 13

ascorbate

Question 14

What cofactors does superoxide dismutase require?

Answer 14

Zn and Cu (extracellularly and cytoplasm), Mn (mitochondria)

Question 15

What is the chemical eqn for Super oxide?

Answer 15

O2-

Question 16

what form of ascorbate is formed when it reacts with SOD?

Answer 16

dehydroascorbate (DHAA)

Question 17

What is hydrogen peroxide generated by?

Answer 17

SOD
ascorbate
Oxidation within peroxisomes
trauma or injury
amine oxidase

Question 18

What is formed when hydrogen peroxide combines iwth superoxide radicals?

Answer 18

hydroxyl radical

Question 19

What produces hydroxyl radicals

Answer 19

-gamma rays
-reactions between hydrogen peroxide and super oxide radicals
-

Question 20

What is the haber-weiss reaction?

Answer 20

Reaction between super oxide radicals and hydrogen peroxide radicals that produces hydroxyl radicals.

Question 21

What catalyses the haber-weiss reaction?

Answer 21

the reduction of ferric iron (Fe3+) to ferrous iron (Fe2+)

Question 22

What are peroxyl, hydroperoxyl and alkoxyl radicals derived from?

Answer 22

superoxide radicals

Question 23

What tissue are peroxyl, hydroperoxyl and alkoxyl radicals most common in and what do they cause?

Answer 23

fatty acid tissue, oxidation.

Question 24

What substance still causes damage to cells but isn’t technically a free radical?

Answer 24

singlet oxygen

Question 25

What generates singlet oxygen

Answer 25

``` lipid peroxidation enzyme reactions (eg respiratory burst) photochemical reactions (eg uv on oxygen). ```

Question 26

How does singlet oxygen occur?

Answer 26

peripheral electron in the oxygen atom is excited to an orbital above the one it normally occupies.

Question 27

What nutrient helps reduce superoxide radicals and what is the equation?

Answer 27

ascorbate (AH2) reduces superoxide to form hydrogen peroxide and dehydroascorbate (DHAA)

Question 28

What nutrient reduces hydrogen peroxide radical?

Answer 28

ascorbate plus hydrogen peroxide goes to 2x water + dehydroascorbate (DHAA)

Question 29

What enzyme reduces super oxide radical

Answer 29

super oxide dismutase (converts superoxide to hydrogen peroxide)

Question 30

What enzymes reduce hydrogen peroxide and what cofactors are they dependent on

Answer 30

glutathione peroxidase (Se), catalase (haem Fe) and myeloperoxidase (haem fe)

Question 31

What nutrients reduce hydroxyl radicals?

Answer 31

``` vitamin C (hydroxide to water, producing semidehydroascorbate) glutathione dihydrolipoic acid uric acid metallothionein CoQ10 ```

Question 32

What nutrients reduce peroxyl radicals

Answer 32

Vitamin E Mn CoQ10 Glutathione

Question 33

What nutrients reduce singlet molecular oxygen

Answer 33

carotenoids Vitamin C lipoic acid

Question 34

How do carotenoids deal with singlet molecular oxygen?

Answer 34

Absorb the energy and release it as heat

Question 35

Which compounds regenerate Vitamin E?

Answer 35

ascorbate Coenzyme Q10 glutathione (GSH - reduced form)

Question 36

Which nutrients regenerate Vitamin C?

Answer 36

Niacin (B3 in coenzyme form NADH) dihydrolipoic acid (reduced state) and lipoic acid (oxidised state) glutathione thioredoxin

Question 37

What do two semi-dehydroascorbate produce

Answer 37

ascorbate + dehydroascorbate

Question 38

What regenerates glutathione?

Answer 38

``` glutathione reductase (+ FAD cofactor) dihydrolipoic acid ```

Question 39

What regenerates CoQ10?

Answer 39

dihydrolipoic acid | thioredoxin (+ FAD selenium dependent coenzyme)

Question 40

Wha tnutrients does lipoic acid regenerate?

Answer 40

CoQ10, Vitamin C, Glutathione

Question 41

Which two nutrients is glutathione peroxidase dependent on?

Answer 41

Se, Fe

Question 42

Which nutrient recycles thioredoxin?

Answer 42

NADPH