Free Radicals and reactive oxygen species

1. Prepared by :
Deepa Devkota
Roll no :07
Human Biology 7th batch
Free radicals and reactive oxygen
species

2. FREE RADICALS
 highly reactive molecular species with an unpaired electron,
persists only for very short duration(of the order of 10–9–10–
12 sec)
 Collide with another molecule and either abstract or donate
an electron to achieve stability

3. Types of free radicals
1. Superoxide, O2
-
2. Hydrogen peroxide, H2O2
3. Hydroxyl radical, OH-
4. Singlet oxygen, 1O2
5. Hydroperoxy radical, HOO-
6. Lipid peroxide radical, ROO-
7. Nitric oxide, NO-
8. peroxynitrite, ONOO-

4. Antioxidants:the scavengers of free radicals
 Present in low
concentration that
significantly delays or
inhibits oxidation of
substrate
 antioxidant sacrifices
itself by becoming
oxidized,one antioxidant
molecule can react with
a single free radical

5. Antioxidants
1. Enzymatic
antioxidants
Superoxide
dismutase,catalase,glutathione
peroxidase,glutathione reductase
2.Nutrient
antioxidants
β- carotene,α tocopherol,ascorbic
acid
3.Metabolic
antioxidants
Bilirubin,uric
acid,ceruloplasmin,ferritin,transferrin,al
bumin,glutathione

6. Reactive oxygen species
 Major oxygen metabolites produced by one electron
reduction of oxygen

9. Hydroxyl radicals are the most potent
ROS

10. Lipid peroxidation by hydroxyl
radical

11. Biological effects of free radicals
 DNA: chemical changes that if not repaired can
inherited to daughter cells
 Proteins: Oxidative damage to sulfhydryl group and
tyrosine residues in protein can lead to formation of
oxygen radicals by non enzymatic reactions
formation of proteins that are recognized as non self
by immune system leading to cross reaction causing
autoimmune diseases

12. Biological effects of free radicals
 Chemical modification of protein or lipids in plasma
low density lipoprotein leads to abnormal LDL which
arenot recognized by liver’s LDL receptors
 Modified LDL is taken by macrophage scavenger
receptor,forms lipid engorged macrophages(LEM),
infiltrate under blood vessel endothelium
 Killing of LEM by high content of unesterified
cholesterol forming atherosclerotic plaques

13. Free radicals and diseases
 Respiratory diseases: destroy endothelium and
cause lung edema
Cigarette smoke contains free radicals and
promotes the production of more free radicals
 Diabetes mellitus: Destruction of islets results in
pathogenesis
 Cataract
 Male infertility: reduce sperm motility and viability
 Ageing process
 Others:
 Parkinson’s disease
 Alzheimer’s disease
 multiple sclerosis, liver cirrhosis

16. REFERENCES
 Harper’s illustrated biochemistry,28th edition
 Marks Dawn B. ,basic medical biochemistry, a
clinical approach
 sciencedirect.com/science/article/pii/S0891584900
002525(retrieved on 17th january,2015)
 slideshare.net/guest371c9f/free-radicals(retrieved
on 15th january 2015)