Cellular Redox Processes and Oxidative Stress Quiz

______ is an element indispensable for life.

When cells use oxygen to generate energy, free radicals are created as a consequence of ATP production by the ______.

These by-products are generally reactive oxygen species (ROS) as well as reactive nitrogen species (RNS) that result from the cellular ______ process.

At low or moderate levels, ROS and RNS exert ______ effects on cellular responses and immune function.

Oxidative stress plays a major part in the development of chronic and degenerative ailments such as cancer, arthritis, aging, autoimmune disorders, cardiovascular and ______ diseases.

The human body has several mechanisms to counteract oxidative stress by producing ______, which are either naturally produced in situ, or externally supplied through foods and/or supplements.

A molecule with one or more unpaired electron in its outer shell is called a __________ radical.

Free radicals are formed from molecules via the breakage of a chemical bond such that each fragment keeps one electron, by cleavage of a radical to give another radical and, also via _______ reactions.

Free radicals include hydroxyl (OH ), superoxide (O2 ˉ), ______ oxide (NO ), nitrogen dioxide (NO2 ), peroxyl (ROO ) and lipid peroxyl (LOO ).Also, hydrogen peroxide (H2O2), ozone (O3), singlet oxygen (1O2), hypochlorous acid (HOCl), nitrous acid (HNO2), peroxynitrite (ONOOˉ), dinitrogen trioxide (N2O3), lipid peroxide (LOOH), are not free radicals and generally called oxidants, but can easily lead to free radical reactions in living organisms.

Biological free radicals are thus highly unstable molecules that have electrons available to react with various organic substrates such as lipids, proteins, DNA Formation of ROS and RNS can occur in the cells by two ways: enzymatic and _________ reactions.

The superoxide anion radical (O2 ˉ) is generated via several cellular oxidase systems such as NADPH oxidase, xanthine oxidase, peroxidases.Once formed, it participates in several reactions yielding various ROS and RNS such as hydrogen peroxide, hydroxyl radical (OH ), peroxynitrite (ONOOˉ), hypochlorous acid (HOCl), etc.H2O2 (a non radical) is produced by the action of several oxidase enzymes, including aminoacid oxidase and xanthine oxidase.The last one catalyses the oxidation of hypoxanthine to xanthine, and of xanthine to uric acid.Hydroxyl radical (OH ), the most reactive free radical in vivo, is formed by the reaction of O2 ˉ with H2O2 in the presence of Fe2+ or Cu+ (catalyst).This reaction is known as the Fenton reaction.

Nitric oxide radical (NO ) is formed in biological tissues from the oxidation of L-arginine to citrulline by nitric oxide __________.