Reactive Oxygen Species

Question 0

How are reactive oxygen species created?

Answer 0

Electrons lost from electron transport chain in oxidative phosphorylation react with O2 or OH.

Question 1

Name some reactive oxygen species.

Answer 1

Superoxide radical = O2-

Hydroxyl radical = .OH

Nitric oxide = NO.

Question 2

How are superoxide radicals neutralised?

Answer 2

O2- converted to hydrogen peroxide (H2O2) by superoxide dismutase (SOD)

Hydrogen peroxide converted to water and oxygen by catalase

Question 3

Give an example of a drug which is an oxidising agent.

Answer 3

Primaquine (anti-malarial)

Question 4

Give examples of toxins which act as oxidising agents.

Answer 4

Paraquat = herbicide (suicide)

Paracetamol = overdose -> damages liver
treat with reducing agent N-acetyl cysteine promptly

Question 5

What are the cellular defences against oxidising agents?

Answer 5

Glutathione (GSH) oxidises to form glutathione disulfide (GSSG).

NADPH reduces GSSG back to GSH so GSH can reduce hydrogen peroxide to water.

Question 6

Name some antioxidants.

Answer 6

NADPH & GSH

Vitamins: ACE

Flavenoids: polyphenols (red wine) & beta-carotene (carrots)

Minerals: selenium & zinc

Question 7

How do reactive oxygen species damage cells? What diseases can be caused by reactive oxygen species?

Answer 7

React with unsaturated lipids to form lipid peroxides, which damage the cell membranes.

Causes cancer, emphysema, pancreatitis, CVD, Crohn’s, rheumatoid arthritis, Type 1 diabetes, Alzheimer’s, ischaemia

Question 8

Describe the oxidative burst.

Answer 8

Leukocytes (neutrophils & monocytes) release superoxide and hydrogen peroxide rapidly, self-destructing and killing bacteria and other cells in the local area.

Catalysed by NADPH oxidase.