L19 Oxidative stress pt 1 Flashcards
- Investigate oxidative stress using cellular models. LOs: - Explain the biochemistry of reactive oxygen species, their origin and the cellular mechanisms of protection against these agents. - Identify some of the methods that can be used to measure ROS and its consequences in cell models. - Identify the links between ROS, irregular biochemical processes and disease.
What are ROS?
Reactive oxygen species are byproducts of aerobic metabolism.
They can act as signaling molecules in physiological function.
What is oxidative stress?
Refers to elevated levels of intracellular ROS.
This damages, proteins, lipids, DNA.
What are the most common reactive oxygen species?
Why does oxygen produce ROS during respiration?
O2 must be reduced (added electrons). This creates superoxides, peroxides, hydroxyl radicals.
Each of these ROS has potential to damage cell, but normally kept relatively stable levels
O2 is stable. Why does the first reduction lead to a cascade in reduction?
O2 beoming radical O2- has negative redox potential, but once formed, positive until water is formed.
Consequence of electron leakage from electron transport chain.
How does the body deal with these ROS?
Enzymes such as superoxide dismutase further reduces molecule, eventually becomes water.
What effect does ionising radation have on water in our body?
Oxidises water, produces ROS
What role does inflammation play in generation of ROS?
Capable of producing ROS.
By action of NADPH oxidase. Found in neutrophils/macrophages/innate cells.
What role do metal ions play in ROS?
If not kept in check, not chelated, cause ‘fenton reaction’ which generates ROS.
H2O2 + Fe2+ = •OH + •OH- + Fe3+
How is the fenton reaction prevented?
Metal binding proteins, ferratin etc, keeps them from reacting.
What role do drugs + chemicals play in ROS?
Can also form ROS.
e.g.
Rotenone (pesticide) is a complex I inhibitor in electron transport chain. Causes electron leakage and therefore formation of ROS.
What are four promoters of ROS?
Ionising radation.
Inflammation.
Metal ions.
Drugs/chemicals (e.g. pesticides, paracetamol)
What does a paracetamol overdose do for ROS?
How is overdose combated?
Paracetamol is broken down into active moiety that generates ROS. Glutathione in liver usually detoxifies this.
But too much paracetamol, not enough glutathione so ROS generates.
Glutathione precursor (N-acetyl cysteine) given to treat, which allows more glutathione to be made by body.
Why is the superoxide produced?
Complex I and III are suseptible to leakage of electrons in mitochondria.
How is superoxide dealt with?
Superoxide dismutase converts to hydrogen peroxide.
Less toxic and damaging, but more stable, does break down after a few days if not broken down.
How is hydrogen peroxide dealt with?
Glutathione peroxidase breaks it down.
Peroxidoxins also.
What does superoxide react with in signaling?
Nitric oxide.
Overproduction of superoxide in presence of NO, creates damaging moiety, peroxynitrite.
This reacts with tyrosine-containing proteins. Nitrates these tyrosines.
How does superoxide damage DNA?
Damages guanine residue. Very suseptible to superoxide.
Converts guanine to 8-oxoguanine. Prevents hydrogen bond with cytosine residue. But damage not significant enough to be repaired and can be passed onto daughter cell.
How can superoxide DNA damage be repaired?
DNA glycoslyases (repair enzymes) can repair this.
What is an AP site?
apurinic or apyrimidinic site. Site on DNA that has neither base.
Result of repaired DNA damage caused by superoxide ion.
Indicator of too much ROS being generated.
