University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2022
Views:

406

Pages:

9
Author:

emaiftAddiniaf5

Section 10.3: Oxygen , Cell Function, and Oxidative Stress §All living processes take place within a redox environment §Redox state is regulated within a narrow range because of redoxsensitive nature of many pathways §Important linked redox pairs (NAD(P)H/NAD(P)+ and GSH/GSSG) help maintain redox conditions §GSH (glutathione) is a key cellular-reducing agent §Reactive oxygen species (ROS)- oxygen accepts single electrons forming unstable derivatives §Superoxide radical, hydrogen peroxide, hydroxyl radical, singlet oxygen §Antioxidants interact with ROS to mitigate damage §Under certain conditions, antioxidant mechanisms are overwhelmed, leading to oxidative stress §Enzyme inactivation, polysaccharide depolymerization, DNA breakage, membrane destruction §Oxidative damage has been linked to 100 human diseases Section 10.3: Oxygen , Cell Function, and Oxidative Stress Figure 10.18 Overview of Oxidative Phosphorylation and ROS Formation in the Mitochondrion §Reactive Oxygen Species §Diatomic oxygen - diradical, meaning it has two unpaired electrons §Electrons can leak out of the ETC and interact with O2 Section 10.3: Oxygen , Cell Function, and Oxidative Stress §Types of reactive oxygen species: §First created is superoxide radical (O2●-), which acts as a nucleophile §O2●- can react with itself to form hydrogen peroxide H2O2 §H2O2 can react with Fe2+ to form hydroxyl radical (●OH), which can initiate autocatalytic radical chain reaction Figure 10.19 Radical Chain Reaction Section 10.3: Oxygen , Cell Function, and Oxidative Stress §H2O2 can react with Fe2+ to form hydroxyl radical (●OH), which can initiate autocatalytic radical chain reaction §Singlet oxygen (1O2) formed from H2O2 or superoxide can be damaging to aromatics and conjugated alkenes Figure 10.19 Radical Chain Reaction Section 10.3: Oxygen , Cell Function, and Oxidative Stress §Also reactive nitrogen species (RNS) §Nitric oxide, nitrogen dioxide, and peroxynitrite §Physiological functions of NO include blood pressure regulation, inhibition of blood clotting, and destruction of foreign cells by macrophages Section 10.3: Oxygen , Cell Function, and Oxidative Stress §Antioxidant Enzyme Systems §To protect against oxidative stress, living organisms have developed several antioxidant defense mechanisms §Four enzymes: superoxide dismutase, glutathione peroxidase, peroxiredoxin, and catalase §Superoxide dismutase forms H2O2 and O2 from superoxide radical §Catalase forms H2O and O2 from H2O2 Section 10.3: Oxygen , Cell Function, and Oxidative Stress Figure 10.21 The Glutathione-Centered System §Glutathione peroxidase uses the reducing agent GSH to control peroxide levels §Reduces H2O2 to form water and transforms organic peroxides to alcohols §Glutathione reductase is also an important enzyme in the glutathione system Section 10.3: Oxygen , Cell Function, and Oxidative Stress Figure 10.22 The Thioredoxin-Centered System §Peroxiredoxins (PRX) are a class of enzymes that detoxify peroxides §Uses thiol-containing peptides like thioredoxin §Thioredoxin is involved in redox reactions mediated by the peroxiredoxin/thioreductase system Section 10.3: Oxygen , Cell Function, and Oxidative Stress Figure 10.23 Selected Antioxidant Molecules §Antioxidant Molecules §a-Tocopherol (vitamin E) is a potent, lipid-soluble radical scavenger §b-carotene, a carotenoid, is a precursor of vitamin A (retinol): a potent, lipid-soluble radical scavenger in membranes §Ascorbat(vit C) protects membranes through two mechanisms: scavenging a variety of ROS in aqueous environments and enhancing the activity of a-tocopherol