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Nutritional Biochemistry > Lecture 7 > Flashcards

Lecture 7 Flashcards

1
Q

What is a free radical

A

A molecule with an unpaired electron

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2
Q

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

A

smog, cigarette smoke, immune response

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3
Q

Name two types of damage free radicals can form

A 
DNA damage (eg nucleus, mitochondria)
Damage to lipids (oxidation, cell membranes)
Protein structure (amino acids,  RBC)
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4
Q

What is an antioxidant

A

a substance that stops damaging effects of free radicals

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5
Q

name 5 antioxidant nutrients

A

Vitamins A, C, E, CoQ10, selenium

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6
Q

What are the 3 main endogenous antioxidants?

A

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

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7
Q

Name 3 exogenous antioxidants

A

Vits A, C, E, lipoic acid

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8
Q

Which nutrients effectively ‘recycle’ each other?

A

ascorbate regenerates vitamin E

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9
Q

What are 5 types of reactive species?

A
  • superoxide radical
  • hydrogen peroxide
  • hydroxyl radical
  • peroxyl
  • carbon centred radicals
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10
Q

How are oxygen centred radicals generated?

A

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
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11
Q

Functions of antioxidants

A
  • 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
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12
Q

Which enzyme produces hydrogen peroxide while removing superoxide radicals?

A

superoxide dismutase

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13
Q

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

A

ascorbate

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14
Q

What cofactors does superoxide dismutase require?

A

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

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15
Q

What is the chemical eqn for Super oxide?

A

O2-

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16
Q

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

A

dehydroascorbate (DHAA)

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17
Q

What is hydrogen peroxide generated by?

A 
SOD
ascorbate
Oxidation within peroxisomes
trauma or injury
amine oxidase
18
Q

What is formed when hydrogen peroxide combines iwth superoxide radicals?

A

hydroxyl radical

19
Q

What produces hydroxyl radicals

A

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

20
Q

What is the haber-weiss reaction?

A

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

21
Q

What catalyses the haber-weiss reaction?

A

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

22
Q

What are peroxyl, hydroperoxyl and alkoxyl radicals derived from?

A

superoxide radicals

23
Q

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

A

fatty acid tissue, oxidation.

24
Q

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

A

singlet oxygen

25
Q

What generates singlet oxygen

A 
lipid peroxidation
enzyme reactions (eg respiratory burst)
photochemical reactions (eg uv on oxygen).
26
Q

How does singlet oxygen occur?

A

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

27
Q

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

A

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

28
Q

What nutrient reduces hydrogen peroxide radical?

A

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

29
Q

What enzyme reduces super oxide radical

A

super oxide dismutase (converts superoxide to hydrogen peroxide)

30
Q

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

A

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

31
Q

What nutrients reduce hydroxyl radicals?

A 
vitamin C (hydroxide to water, producing semidehydroascorbate)
glutathione
dihydrolipoic acid
uric acid
metallothionein
CoQ10
32
Q

What nutrients reduce peroxyl radicals

A

Vitamin E
Mn
CoQ10
Glutathione

33
Q

What nutrients reduce singlet molecular oxygen

A

carotenoids
Vitamin C
lipoic acid

34
Q

How do carotenoids deal with singlet molecular oxygen?

A

Absorb the energy and release it as heat

35
Q

Which compounds regenerate Vitamin E?

A

ascorbate
Coenzyme Q10
glutathione (GSH - reduced form)

36
Q

Which nutrients regenerate Vitamin C?

A

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

37
Q

What do two semi-dehydroascorbate produce

A

ascorbate + dehydroascorbate

38
Q

What regenerates glutathione?

A 
glutathione reductase (+ FAD cofactor)
dihydrolipoic acid
39
Q

What regenerates CoQ10?

A

dihydrolipoic acid

thioredoxin (+ FAD selenium dependent coenzyme)

40
Q

Wha tnutrients does lipoic acid regenerate?

A

CoQ10, Vitamin C, Glutathione

41
Q

Which two nutrients is glutathione peroxidase dependent on?

A

Se, Fe

42
Q

Which nutrient recycles thioredoxin?

A

NADPH

Nutritional Biochemistry (4 decks)

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