Oxygen Flashcards
oxygen is essential for all life of ____ organisms
aerobic
O2 is highly reactive in ____ reactions at ____ temperatures
combustion; high
O2 is relatively inert at _____
body temperatures
O2 has high ____ for ____ reactions
activation energy; oxidation
about 90% of oxygen usage is committed to _____
oxidative phosphorylation
oxidation is the ___ of electrons or an ____ in oxidation state by a molecule, atom, or ion
loss; increase
reduction is the ___ of elections or a ____ in oxidation state by a molecule, atom, or ion
gain; decrease
the formal oxidation state is the hypothetical ___ that an atom would have if all bonds to atoms of different elements were 100% ____
charge; ionic
oxidation/reduction reactions happen simultaneously; each alone are called a ____
half-reaction
reactivity of O2 requires ___ or ____
high heat; activation energy
at body temperatures, activation of O2 is always activated by ____
metal ions (iron, copper, or manganese)
____ are partially reduced, reactive forms of oxygen
reactive oxygen species (ROS)
the first reduction product is the anion radical _____, which is in equilibrium with the weak acid, _____
superoxide; hydroperoxyl radical (pKa 4.5)
reduction of superoxide yields ____
hydrogen peroxide (H2O2)
reduction of hydrogen peroxide causes a homolytic cleavage reaction which releases ____ and _____
hydroxyl radical; hydroxide ion
____ is the end product of complete reduction of O2
water
____ occurs when the rate of ROS generation exceeds the ability to neutralize them
oxidative stress
oxidative stress results in an increase in ____ to ____ (cell proteins, lipids, and DNA)
oxidative damage; biomolecules
reactive oxygen species (ROS) used by ____ to destroy pathogens; also a feature of _____ diseases like arthritis, atherosclerosis, SLE, or diabetes)
immune cells; inflammatory
disturbances in the normal redox state of cells can cause toxic effects through the production of ____ and ____ that damage all components of the cell, including proteins, lipids and DNA
peroxides; free radicals
most prevalent ROS in blood and tissues is ____, which is a stable molecule unless reacted with metal
hydrogen peroxide (H2O2)
____ is most reactive and damaging species
OH radical
other ROS include ____, ____ and _____
superoxide anion (ion and radical); hypochlorite ion; hydroperoxyl radical
a radical is a cluster of atoms, one of which contains an ____ in its outermost shell of electrons
unpaired electron
ROS formed by 3 major mechanisms in vivo:
- by reaction of oxygen with de-compartmentalized metal ions (Fenton and Haber-Weiss rxns)
- as a side rxn of mitochondrial electron transport
- normal enzymatic rxns (formation of H2O2 by fatty acid oxidases in the peroxisome)
fenton first described the oxidizing power of ____ and ____; this rxn generates the strong oxidant ____ (____ catalyzes the same rxn)
Fe2+ ; H2O2; hydroxyl radical; Cu+
the H-W reaction describes the production of hydroxyl radical from ____ and _____
superoxide anion radical; hydrogen peroxide
under phys. conditions, the H-W rxn is catalyzed by ____ metal ions
redox-active
oxidative stress is an imbalance betw ____ and ____ systems
pro-oxidant; antioxidant
ROS can be generated by the _____ in mitochondria; can be caused by ____ injury following myocardial infarction
mitochondrial electron transport chain; ischemia/reperfusion
ROS generated by activation of ____ during inflammatory conditions (example is myeloperoxidase converting H2O2 and Cl- to hypochlorous acid (HOCl)
polymorphonuclear leukocytes (PMN)
one of the most sensitive sites of ROS damage is at the ____ because they are rich in _____ which react readily with ROS
cell membrane; polyunsaturated fatty acids (PUFA)
damage to cell membrane leads to reduced ____ and ____ and can result in ____
integrity; function; apoptosis
the hydroxyl radical is known to react with all components of the DNA molecule, damaging both the ____ and ____ bases and also the ____
purine; pyrimidine; deoxyribose backbone
most extensively studied DNA lesion is ____
8-OH-G (8-oxoguanine or 8-hydroxygunanine)
permanent mod. of genetic material resulting from these oxidative damage incidents is the first step to ____, ____ and ____
mutagenesis; carcinogenesis; aging
the side chains of all ____ residues of proteins , in particular ____ and ____ residues are susceptible to oxidation by the action of ROS
amino acid; cysteine; methionine
cells of the ___ must make hydrogen peroxide in order to attach ____ to ____ in the synthesis of thyroxine
thyroid gland; iodine atoms; thyroglobulin
____ and ____ must generate ROS in order to kill some types of bacteria they engulf by phagocytosis
macrophages; neutrophils
defense mechanisms against free radical -induced oxidative stress involve:
- preventive mechanisms
- repair mechanisms
- physical defenses
cells have a variety of ____ defenses against the harmful effects of ROS
enzymatic
____ converts 2 superoxide anions into a molecule of hydrogen peroxide and oxygen
superoxide dismutase (SOD)
___ converts hydrogen peroxide to water and oxygen
catalase
small molecules that are antioxidant
vitamins A, C, and E and uric acid
diseases developed by ROS
inflammation (arthritis, SLE, diabetic complications, reperfusion)
infection
cancer-mutagenesis
aging
