Free Radicals Flashcards
what is a free radical
an atom or group of atoms (molecule) with one or more unpaired electrons
what produces free radicals (3)
energy transfer (electrons), redox, enzymatic reactions
what is homolytic cleavage (example)
A-B becomes A* + B*
what is an example of energy transfer reaction that produced free radicals
H2O + hv –> HO* + H*
what is an example reaction of an enzymatic process that produced free radicals
O2 + e- –> O2*-
what are 3 examples of normal bodily enzymatic processes that produce free radicals (O2 + e- –> O2*-)
- phagocyte respiration burst
- mitochondrial respiration
- intracellular enzymes, metabolism
what is the fenton reaction
Fe2+ + H2O2 –> Fe3+ + HO* + HO-
which is the most reactive radical
OH radical
what kind of diseases do free radicals cause
lots of them!!
what are 4 things that can happen with macromolecule free radicals
mutation, catabolism, inactivation signalling
what 2 things can happens once macromolecule free radicals cause signalling
toxicity or protection (apoptosis)
what kind of species is H2O2
a pro-radical, just 1 step away from a free radical
what are 2 main initiator free radicals
O2- and HO
what is superoxide
O2*-
What is hydroxyl radical
HO*
what is a common reaction that makes the hydroxyl radical
H2O + hv –> HO- +H
what is an example of a good free radical
NO*
what is the difference with superoxide and normal diatomic oxygen
there is 1 more elctron
how reactive is OH*
very
what are reactive oxygen species
species that are derived from oxygen that are or have the ability to form free radicals
what are reactive oxygen species compared to oxygen
they are more oxidizing that oxygen
are all reactive oxygen species free radicals
no
is hydrogen peroxide a free radical
no
is singlet oxygen a free radical
no
what can cause the formation of singlet oxygen
light and photosensitizer
what is singlet oxygen diff with oxygen
two electrons fill one orbital and none in other (compared to one in ech in normal oxygen)
why is singlet oxygen a better oxidizer than oxygen
because it has has an empty orbital that it wants to fill with an electron
why is oxygen a diratical
because it has 2 unpaired electrons in its orbitals
why is oxygen unreactive
because the electrons have parallel spins
is singlet oxygen a ROS
yes
is singlet oxygen an electrophile or nucleophile
electrophile
is superoxide a reductant or oxidant
either
what is peroxynitrite
ONOO-
what is the reaction that forms peroxynitrite
O2*- + NO+ –> ONOO-
what is mitochondrial aconitase
an enzyme which is a target for ROS
why does aconitase react with superoxide
because it has iron that is solvent exposed which is electrophilic and reacts with superoxide (nucleophilic)
when can mitochondrial aconitase become a target for ROS attack
when the system is overwhelmed in trying to combat free radicals
what is the main reaction that happens in phagocytosis
NADPH + O2 –> NADP+ + O2*-
what happens after superoxide is produced in phagocytosis
it forms H2Oh then HOCl
what is the main enzyme responsible in phagocytosis
NADPH oxidase
what is consumed to make superoxide in phagocytosis
NADPH
what is the respiratory burst
oxidation of NADPH in order to generate superoxide
what activates the phagocytosis response
microorganisms and inflammatory mediators
what do microorganisms and inflammatory mediators activate
NADPH oxidase enzyme complex to crease phagocytosis
what is MPO and what does it do
enzyme that produces HOCl, called myeloperoxidase
how is MPO (myeloperoxidase) activated
superoxide is converted into H2O2 which activates MPO to generate HOCl
what enzymes helps produce HOCl
MPO
which complexes in the mitochondria make superoxide
1 and 3
how can some drugs effect ETC and cause ROS
they interfere with electron transport therefore electrons will leak and react with oxygen
how can drug metabolism cause ROS
from cytochrome P450 enzymes
how can cytochrome P450 enzymes lead to ROS production
an iron complex becomes unstable then it breaks apart and releases superoxide
when does xanthine oxidase work
activity occurs during oxidative stress/ proteolytic cleavage of the enzyme (ex: during ischemia reperfusion)
what does xanthine oxidase produce
mostly H2O2 and also superoxide
what does xanthine reductase do
lets NAD+ receive electrons
why are quinones bad
they are electron deficient and unstable
what can semiquinones do with the presence of oxygen
do redox cycling to make more and more superoxide radicals
Inhibition of mitochondrial respiration can lead to ROS, through inhibition of which complex
1 and 3
what happens in the redox cycle
semiquinone gets recycled with NADPH P450 reductase to create more and more superoxide anions (needs oxygen present)
what does superoxide often turn into
H2O2
with Fe++ present, what can H2O2 turn into
HO* hydroxyl radical
what happens with H2O2 and transition metals
fenton reaction
can H2O2 cross membranes
yes
is there free iron in the body and why
no because the fenton reaction is very toxic, so the body regulates iron very tight
what is the reaction rate with HO* like
diffisuion limited
are there specific OH* scavengers
no
what is the net reaction that makes the hydroxyl radical
O2- + H2O2 –> O2 + OH- + OH
what is the catalyst in the reaction : O2- + H2O2 –> O2 + OH- + OH
iron
what is the primary target for biological effects of ionizing radiation
DNA
what is the direct action of ionizing radiation damaging DNA
photon causes ionizing electron to be produced, electron travels and directly causes DNA damage
what is the indirect action of ionizing radiation damaging DNA
photon causes ionizing electron to be produced, electron interacts with water to produce radical ion species (OH*) which can damage DNA
is indirect or direct action of radiation damage to DNA more likely
indirect is more likely
which is the most susceptible base that reacts with DNA
guanine
what is a useful marker of oxidative DNA damage
8-hydroxydeoxyguanosine
what is the deal with 8-hydroxydeoxyguanosine
it is a useful marker of oxidative DNA damage
why is 8-hydroxydeoxyguanosine a useful marker of oxidative DNA damage
because guanine is the most likely base to be modified
what does lipid peroxidation do
cause physical damage to membranes
what kind of fats are highly susceptible to oxidation
polyunsaturated fatty acids
what happens once oxidized fatty acid products are made
they have biological activity
how can oxidized fatty acids be made
as products from both enzymatic and non enzymatic reactions
what are some examples of oxidized fatty acid products
hydroxyperoxides, isoprostanes, prostaglandins/leukotrienes, thromboxanes
why is damaging proteins more complicated compared to DNA
lots of differenta mino acids, so lots of different things can happen (sulferoxidation, crosslinkgs, carbonyls…)
is sulfer often oxidized or reduced and why
oxidized because it is nucelophilic
do proteins or DNA have more complex ways to be damaged
proteins
what can happen to protein or enzyme activity with oxidative modification
they usually lose activity, but sometimes they gain it
what happens to immunogenicity with damaged proteins and why
increased because the immune system recognizes it as foreign
what are 2 ways that glutathione conjugation can occur
either catalyzed by glutathione S-transferases or non-enzymatic
where is glutathione usually found (in the cell)
cytosol and endoplasmic reticulum
what is special about the structure of glutathione
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)
what is the SH group called
thiol
what is the reaction that catalase does
2H2O –> O2 +2H2O
what kind of enzyme is catalase
heme enzyme
what is the role of catalase
gets rid of H2O2
what is the role of glutathione peroxidase
gets rid of H2O2 and lipid-OOH
what is a difference with glutathione and catalase
catalase only does H2O2, glutathione does that and more
is glutathione or catalase more versatile
glutathione
what are 2 main enzymes for peroxide detoxification
glutathione peroxidase and catalase
what is the general glutathione peroxidase reaction
2GSH + ROOH –> GSSG + ROH + H2O
what is lipid-OOH
hydroperoxide
what is hydroperoxide
Lipid-OOH
what does lipid-ooh and glutathione peroxidase generate (like with the lipid molecule)
lipid-OH (alcohol) which is non toxic
what is the cofactor for glutathione peroxidase
selenoenzyme
what are 2 superoxide detoxification antioxidant enzymes
Cu/Zn SOD and Mn SOD
where is Cu/Zn SOD
cytosol, also extracellular
where is Mn SOD
mitochondria (coded in nucleus)
what kind of SOD is found in the cytosol
Cu/Zn
what kind of SOD is found extracellularly
Cu/Zn
what kind of SOD is found in the mitochondria
Mn
what reaction does SOD catalyse
2O2*- +2H+ –> H2O2 + O2
what happens with Mn SOD knockout in mice
death in 10 days, damaged mitochondria and neurodegeneration
what happens with Cu/Zn SOD knockout in mice
increased O2 sensitivity, neurological damage and cancers
is Mn or Cu/Zn SOD worse to not have
Mn
what is the main form of Vitamin E
alpha-tocopherol
what is alpha-tocopherol
the main form of Vitamin E
what is the structure of the main form of alpha-tocopherol like
long fatty acid tail, lipid soluble
what is the major function of vitamin E
fat soluble chain breaking antioxidant
how is alpha-tocopherol an antioxidant (2)
peroxyl radical scavenger, protects polyunsaturated fats within membranes and lipoproteins
what is the major function of vitamin C
reducing agent in a number of different reactions, most important is hydroxylation of proline residues in collagen
is vitamin E fat or water soluble
fat
is vitamin C fat or water soluble
water
what does vit C deficiency cause and why
scurvy due to its role in PTM of collagen
where is a location with very high amounts of Vit C in the body
in neurons, but stored really well in the body at high concentrations
what does Vit C do to free radicals
scavenge them
what kind of substrates cause superoxide or H2O2 production by cytochdrome P450
weakly binding ones
does catalase require a cofactor
no
what functional group is found in both Vit E and C
hydroxyl group
what is the important structural feature of Vit E
the OH group
