Free radicals are highly reactive molecules with unpaired electrons that persist for very short durations. They react with other molecules by donating or abstracting electrons to achieve stability. Common types of free radicals include superoxide, hydrogen peroxide, and hydroxyl radicals. Antioxidants help scavenge free radicals and delay or inhibit oxidation, with one antioxidant typically reacting with one free radical. Enzymatic antioxidants include superoxide dismutase and catalase, while nutrient antioxidants include beta-carotene and vitamin E. Reactive oxygen species are oxygen metabolites produced from one-electron reductions of oxygen that can damage DNA, proteins, and lipids, potentially leading to diseases like cancer, diabetes, and age-related illnesses.

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)