Oxygen Metabolism Flashcards
What does ROS stand for?
Reactive oxygen species
How would you chemically describe ROS?
Highly reactive oxygen containing free radicals
Which radical is the most potent ROS?
Hydroxyl radical
Name some exogenous sources or ROS.
UV radiation, tobacco, drugs
Name some endogenous sources or ROS.
NADPH, electron transport chain
How is oxygen converted to an ROS?
- Oxygen is reduced by an electron to form superoxide
- Superoxide is reduced further to hydrogen peroxide
- Hydrogen peroxide is reduced further to form hydroxyl radical which is later reduced to water
Which reaction catalyses the formation of a hydroxyl radical from hydrogen peroxide?
Fenton reaction
Give the Fenton reaction
H2O2 + Fe2+ > Fe3+ + OH- + OH•
Which reaction produces the hydroxyl radical from the superoxide?
Haber-Weiss reaction
Give the Haber-Weiss reaction
O2•– + H2O2 + H+ > O2 + OH- + OH•
The Fenton reaction and the Haber-Weiss reaction can be combined to forma series of 4 reactions - the Haber-Weiss Cycle. Write this out.
- Fe2+ + H2O2 > Fe3+ + OH- + OH• [Fenton reaction]
- OH• + H2O2 > H2O + O2•– + H+
- O2•– + H+ + H2O2 > O2 + OH• + H2O [Haber-weiss reaction]
- Fe2+ + OH• + H+ > Fe3+ + H2O
Are hydroxyl radicals lipid soluble?
Yes
Which molecules do free radicals damage?
Proteins, lipids, carbohydrates and nucleic acids
Which cell organelles membranes do free radicals damage? What is the effect of this?
Nucleus, mitochondria, ER. Results in increased permeability of the membrane resulting in an influx of calcium, sodium and water.
Name the immune defence against bacteria that involves the sudden release of ROS.
Respiratory burst
Which cells release a respiratory burst?
Neutrophils, macrophages, monocytes
Which compound is produced by neutrophils to damage bacterial cell membranes? It combines H2O2 with Cl-.
Hypochlorite
The absence of which enzyme prevents the formation of ROS?
NADPH oxidase
What are the consequences of no ROS formation?
Build of pathogens in phagocytes. They can engulf not kill them. Leads to severe skin infections.
What is cellular compartmentalisation?
Respiratory burst that takes place in phagosomes so harmful chemicals aren’t released and damage healthy tissue.
Name some key antioxidant enzymes.
Superoxide dismutase
Catalase
Glutathione peroxidase
What is the function of catalase?
Catalyses hydrogen peroxide to water + O2. Protects white blood cells from own respiratory burst.
What is the function of glutathione peroxidase?
Catalyses reduction of H2O2 to water + disulphide
Name some key antioxidant vitamins.
Vitamin E and C
What does vitamin E do?
Protects against lipid peroxidation. Terminates free radical propagation.
What does vitamin C do?
Reacts with superoxide & hydroxyl radical, offers protection
