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pmcol 303 > Free Radicals > Flashcards

Free Radicals Flashcards

1
Q

what is a free radical

A

an atom or group of atoms (molecule) with one or more unpaired electrons

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2
Q

what produces free radicals (3)

A

energy transfer (electrons), redox, enzymatic reactions

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3
Q

what is homolytic cleavage (example)

A

A-B becomes A* + B*

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4
Q

what is an example of energy transfer reaction that produced free radicals

A

H2O + hv –> HO* + H*

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5
Q

what is an example reaction of an enzymatic process that produced free radicals

A

O2 + e- –> O2*-

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6
Q

what are 3 examples of normal bodily enzymatic processes that produce free radicals (O2 + e- –> O2*-)

A
  • phagocyte respiration burst
  • mitochondrial respiration
  • intracellular enzymes, metabolism
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7
Q

what is the fenton reaction

A

Fe2+ + H2O2 –> Fe3+ + HO* + HO-

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8
Q

which is the most reactive radical

A

OH radical

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9
Q

what kind of diseases do free radicals cause

A

lots of them!!

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10
Q

what are 4 things that can happen with macromolecule free radicals

A

mutation, catabolism, inactivation signalling

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11
Q

what 2 things can happens once macromolecule free radicals cause signalling

A

toxicity or protection (apoptosis)

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12
Q

what kind of species is H2O2

A

a pro-radical, just 1 step away from a free radical

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13
Q

what are 2 main initiator free radicals

A

O2- and HO

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14
Q

what is superoxide

A

O2*-

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15
Q

What is hydroxyl radical

A

HO*

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16
Q

what is a common reaction that makes the hydroxyl radical

A

H2O + hv –> HO- +H

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17
Q

what is an example of a good free radical

A

NO*

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18
Q

what is the difference with superoxide and normal diatomic oxygen

A

there is 1 more elctron

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19
Q

how reactive is OH*

A

very

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20
Q

what are reactive oxygen species

A

species that are derived from oxygen that are or have the ability to form free radicals

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21
Q

what are reactive oxygen species compared to oxygen

A

they are more oxidizing that oxygen

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22
Q

are all reactive oxygen species free radicals

A

no

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23
Q

is hydrogen peroxide a free radical

A

no

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24
Q

is singlet oxygen a free radical

A

no

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25
Q

what can cause the formation of singlet oxygen

A

light and photosensitizer

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26
Q

what is singlet oxygen diff with oxygen

A

two electrons fill one orbital and none in other (compared to one in ech in normal oxygen)

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27
Q

why is singlet oxygen a better oxidizer than oxygen

A

because it has has an empty orbital that it wants to fill with an electron

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28
Q

why is oxygen a diratical

A

because it has 2 unpaired electrons in its orbitals

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29
Q

why is oxygen unreactive

A

because the electrons have parallel spins

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30
Q

is singlet oxygen a ROS

A

yes

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31
Q

is singlet oxygen an electrophile or nucleophile

A

electrophile

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32
Q

is superoxide a reductant or oxidant

A

either

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33
Q

what is peroxynitrite

A

ONOO-

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34
Q

what is the reaction that forms peroxynitrite

A

O2*- + NO+ –> ONOO-

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35
Q

what is mitochondrial aconitase

A

an enzyme which is a target for ROS

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36
Q

why does aconitase react with superoxide

A

because it has iron that is solvent exposed which is electrophilic and reacts with superoxide (nucleophilic)

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37
Q

when can mitochondrial aconitase become a target for ROS attack

A

when the system is overwhelmed in trying to combat free radicals

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38
Q

what is the main reaction that happens in phagocytosis

A

NADPH + O2 –> NADP+ + O2*-

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39
Q

what happens after superoxide is produced in phagocytosis

A

it forms H2Oh then HOCl

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40
Q

what is the main enzyme responsible in phagocytosis

A

NADPH oxidase

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41
Q

what is consumed to make superoxide in phagocytosis

A

NADPH

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42
Q

what is the respiratory burst

A

oxidation of NADPH in order to generate superoxide

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43
Q

what activates the phagocytosis response

A

microorganisms and inflammatory mediators

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44
Q

what do microorganisms and inflammatory mediators activate

A

NADPH oxidase enzyme complex to crease phagocytosis

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45
Q

what is MPO and what does it do

A

enzyme that produces HOCl, called myeloperoxidase

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46
Q

how is MPO (myeloperoxidase) activated

A

superoxide is converted into H2O2 which activates MPO to generate HOCl

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47
Q

what enzymes helps produce HOCl

A

MPO

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48
Q

which complexes in the mitochondria make superoxide

A

1 and 3

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49
Q

how can some drugs effect ETC and cause ROS

A

they interfere with electron transport therefore electrons will leak and react with oxygen

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50
Q

how can drug metabolism cause ROS

A

from cytochrome P450 enzymes

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51
Q

how can cytochrome P450 enzymes lead to ROS production

A

an iron complex becomes unstable then it breaks apart and releases superoxide

52
Q

when does xanthine oxidase work

A

activity occurs during oxidative stress/ proteolytic cleavage of the enzyme (ex: during ischemia reperfusion)

53
Q

what does xanthine oxidase produce

A

mostly H2O2 and also superoxide

54
Q

what does xanthine reductase do

A

lets NAD+ receive electrons

55
Q

why are quinones bad

A

they are electron deficient and unstable

56
Q

what can semiquinones do with the presence of oxygen

A

do redox cycling to make more and more superoxide radicals

57
Q

Inhibition of mitochondrial respiration can lead to ROS, through inhibition of which complex

A

1 and 3

58
Q

what happens in the redox cycle

A

semiquinone gets recycled with NADPH P450 reductase to create more and more superoxide anions (needs oxygen present)

59
Q

what does superoxide often turn into

A

H2O2

60
Q

with Fe++ present, what can H2O2 turn into

A

HO* hydroxyl radical

61
Q

what happens with H2O2 and transition metals

A

fenton reaction

62
Q

can H2O2 cross membranes

A

yes

63
Q

is there free iron in the body and why

A

no because the fenton reaction is very toxic, so the body regulates iron very tight

64
Q

what is the reaction rate with HO* like

A

diffisuion limited

65
Q

are there specific OH* scavengers

A

no

66
Q

what is the net reaction that makes the hydroxyl radical

A

O2- + H2O2 –> O2 + OH- + OH

67
Q

what is the catalyst in the reaction : O2- + H2O2 –> O2 + OH- + OH

A

iron

68
Q

what is the primary target for biological effects of ionizing radiation

A

DNA

69
Q

what is the direct action of ionizing radiation damaging DNA

A

photon causes ionizing electron to be produced, electron travels and directly causes DNA damage

70
Q

what is the indirect action of ionizing radiation damaging DNA

A

photon causes ionizing electron to be produced, electron interacts with water to produce radical ion species (OH*) which can damage DNA

71
Q

is indirect or direct action of radiation damage to DNA more likely

A

indirect is more likely

72
Q

which is the most susceptible base that reacts with DNA

A

guanine

73
Q

what is a useful marker of oxidative DNA damage

A

8-hydroxydeoxyguanosine

74
Q

what is the deal with 8-hydroxydeoxyguanosine

A

it is a useful marker of oxidative DNA damage

75
Q

why is 8-hydroxydeoxyguanosine a useful marker of oxidative DNA damage

A

because guanine is the most likely base to be modified

76
Q

what does lipid peroxidation do

A

cause physical damage to membranes

77
Q

what kind of fats are highly susceptible to oxidation

A

polyunsaturated fatty acids

78
Q

what happens once oxidized fatty acid products are made

A

they have biological activity

79
Q

how can oxidized fatty acids be made

A

as products from both enzymatic and non enzymatic reactions

80
Q

what are some examples of oxidized fatty acid products

A

hydroxyperoxides, isoprostanes, prostaglandins/leukotrienes, thromboxanes

81
Q

why is damaging proteins more complicated compared to DNA

A

lots of differenta mino acids, so lots of different things can happen (sulferoxidation, crosslinkgs, carbonyls…)

82
Q

is sulfer often oxidized or reduced and why

A

oxidized because it is nucelophilic

83
Q

do proteins or DNA have more complex ways to be damaged

A

proteins

84
Q

what can happen to protein or enzyme activity with oxidative modification

A

they usually lose activity, but sometimes they gain it

85
Q

what happens to immunogenicity with damaged proteins and why

A

increased because the immune system recognizes it as foreign

86
Q

what are 2 ways that glutathione conjugation can occur

A

either catalyzed by glutathione S-transferases or non-enzymatic

87
Q

where is glutathione usually found (in the cell)

A

cytosol and endoplasmic reticulum

88
Q

what is special about the structure of glutathione

A

it has an SH which is electron rich, it can act as a target for free radicals (acts as buffer to protect against free radicals)

89
Q

what is the SH group called

A

thiol

90
Q

what is the reaction that catalase does

A

2H2O –> O2 +2H2O

91
Q

what kind of enzyme is catalase

A

heme enzyme

92
Q

what is the role of catalase

A

gets rid of H2O2

93
Q

what is the role of glutathione peroxidase

A

gets rid of H2O2 and lipid-OOH

94
Q

what is a difference with glutathione and catalase

A

catalase only does H2O2, glutathione does that and more

95
Q

is glutathione or catalase more versatile

A

glutathione

96
Q

what are 2 main enzymes for peroxide detoxification

A

glutathione peroxidase and catalase

97
Q

what is the general glutathione peroxidase reaction

A

2GSH + ROOH –> GSSG + ROH + H2O

98
Q

what is lipid-OOH

A

hydroperoxide

99
Q

what is hydroperoxide

A

Lipid-OOH

100
Q

what does lipid-ooh and glutathione peroxidase generate (like with the lipid molecule)

A

lipid-OH (alcohol) which is non toxic

101
Q

what is the cofactor for glutathione peroxidase

A

selenoenzyme

102
Q

what are 2 superoxide detoxification antioxidant enzymes

A

Cu/Zn SOD and Mn SOD

103
Q

where is Cu/Zn SOD

A

cytosol, also extracellular

104
Q

where is Mn SOD

A

mitochondria (coded in nucleus)

105
Q

what kind of SOD is found in the cytosol

A

Cu/Zn

106
Q

what kind of SOD is found extracellularly

A

Cu/Zn

107
Q

what kind of SOD is found in the mitochondria

A

Mn

108
Q

what reaction does SOD catalyse

A

2O2*- +2H+ –> H2O2 + O2

109
Q

what happens with Mn SOD knockout in mice

A

death in 10 days, damaged mitochondria and neurodegeneration

110
Q

what happens with Cu/Zn SOD knockout in mice

A

increased O2 sensitivity, neurological damage and cancers

111
Q

is Mn or Cu/Zn SOD worse to not have

A

Mn

112
Q

what is the main form of Vitamin E

A

alpha-tocopherol

113
Q

what is alpha-tocopherol

A

the main form of Vitamin E

114
Q

what is the structure of the main form of alpha-tocopherol like

A

long fatty acid tail, lipid soluble

115
Q

what is the major function of vitamin E

A

fat soluble chain breaking antioxidant

116
Q

how is alpha-tocopherol an antioxidant (2)

A

peroxyl radical scavenger, protects polyunsaturated fats within membranes and lipoproteins

117
Q

what is the major function of vitamin C

A

reducing agent in a number of different reactions, most important is hydroxylation of proline residues in collagen

118
Q

is vitamin E fat or water soluble

A

fat

119
Q

is vitamin C fat or water soluble

A

water

120
Q

what does vit C deficiency cause and why

A

scurvy due to its role in PTM of collagen

121
Q

where is a location with very high amounts of Vit C in the body

A

in neurons, but stored really well in the body at high concentrations

122
Q

what does Vit C do to free radicals

A

scavenge them

123
Q

what kind of substrates cause superoxide or H2O2 production by cytochdrome P450

A

weakly binding ones

124
Q

does catalase require a cofactor

A

no

125
Q

what functional group is found in both Vit E and C

A

hydroxyl group

126
Q

what is the important structural feature of Vit E

A

the OH group

pmcol 303 (25 decks)

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