10 minutes video about Reactive Oxygen Species

What are the Reactive Oxygen Species ?

Reactive Oxygen Species(ROS) are a type of unstable molecule that contains oxygen and that easily reacts with other molecules in a cell. In a biological context, ROS are obligatory byproducts of biochemical pathways such as glycolysis and photosynthesis. For example, the enzyme cytochrome c oxidase which plays role in the respiratory electron transport chain produce H2O from the O2. This enzyme adds 4 hydrogen atoms to molecular O2 and produces O2. The one-electron reduction of ground state molecular oxygen produces “superoxide ( •O2-)”, a further single electron reduction produces hydrogen peroxide(H2O2). Furthermore, these two ROS can form highly reactive hydroxyl radical(•OH). For another instance some organisms use flavin-containing compound or chlorophyll as photosensitizer which they able harvesting the light and energizing molecular oxygen, forming singlet oxygen which as high-level energy and reactive to some essential amino acids and lipids.

How is it Created?

Reactive Oxygen Species
Reactive Oxygen Species and their transmutations

O2 itself is a totally harmless molecule as in its ground state. It has two unpaired electrons with parallel spin which makes it paramagnetic and, hence, unlikely to participate in reactions with organic molecules unless it is activated. However, when oxygen is exposed to high-energy or electron-transferring chemical reactions, it can be converted to various highly reactive chemical forms collectively designated ‘‘reactive oxygen species(ROS)’’ Reactivity of molecular oxygen can be increased by removing the spin restriction. This occurs when a single electron is added or when energy transferred to oxygen from a photosensitizer.

Effects of ROS

ROS have unpaired electrons at outer orbital or higher energy in comparison with ground state. Therefore ROS may steal an electron from molecules in the cell and trigger chain reaction what oxidized molecule steal an electron from the near molecule which has paired electron. Furthermore this reaction cause cell injury. ROS are toxic to biological organisms because they oxidize lipids, proteins, DNA, and carbohydrates, resulting in the breakdown of normal cellular, membrane, and reproductive functions. Oxidation of protein, lipid, and DNA changes the structure and function of key cellular constituents, resulting in mutation, cell damage, and death. ROS are implicated such diseases like coronary heart disease, dementia, cataract, stroke, infertility, cancer and aging process. Consequently, organisms have been evolved various mechanism to protect themselves against ROS.

Sources and further reading:

1)Benzie IF. Evolution of antioxidant defense mechanisms. Eur J Nutr. 2000 Apr;39(2):53-61.

2)Rodriguez R, Redman R. Balancing the generation and elimination of reactive oxygen species. Proc Natl Acad Sci U S A. 2005 Mar 1;102(9):3175-6.

3)Pallavi Sharma, Ambuj Bhushan Jha, Rama Shanker Dubey, and Mohammad Pessarakli, “Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions,” Journal of Botany, vol. 2012, Article ID 217037, 26 pages, 2012.


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