Free Radicals and Anti-Oxidants Definition lect 6

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22 Questions

What is the definition of a free radical?

A molecule with one or more unpaired electrons in its outer orbital

What are the products of the partial reduction of oxygen that are highly reactive?

Superoxide anion radical, hydroperoxyl radical, hydrogen peroxide, hydroxyl radical, lipid peroxide radical

What are the important characteristics of reactive oxygen species (ROS)?

Extreme reactivity, short life span, generation of new ROS by chain reaction, damage to various tissues

What is the percentage of oxygen taken up in the body that is converted to free radicals?


Which type of anti-oxidants can inhibit the initial production of free radicals?

Catalase and glutathione peroxidase

What role do preventive anti-oxidants play in the process of lipid peroxidation?

They prevent the initial production of free radicals

What is the primary event during the initiation phase of lipid peroxidation?

Formation of R' (carbon centered radical)

Which of the following is a chain breaking anti-oxidant?

Vitamin E

What is the net result of reactions 2 and 3 during the propagation phase of lipid peroxidation?

Conversion of R' to ROOH (hydroperoxide)

Which anti-oxidant is the aqueous phase antioxidant?

Vitamin C

What produces superoxide anion by a process of respiratory burst during phagocytosis?

NADPH oxidase

Which enzyme is responsible for producing nitric oxide (NO) from arginine?

Nitric oxide synthase

What can cause photolysis of oxygen to produce singlet oxygen?

Light of appropriate wavelengths

Which enzyme is manganese dependent and is involved in scavenging superoxide radicals?

Superoxide dismutase

What enzyme is used for the removal of H2O2 when it is generated in large quantities?


What is the clinical significance of chronic inflammatory diseases like rheumatoid arthritis?

They are involved in pathogenesis due to ROS-induced tissue damage

What is the cause of retrolental fibroplasia (retinopathy of prematurity) in premature infants treated with pure oxygen for a long time?

Free radicals causing thromboxane release and sustained vascular contracture

What is the cause of reperfusion injury after myocardial ischemia?

Conversion of hypoxanthine to xanthine and superoxide anion

What causes low-density lipoproteins (LDL) to be deposited under the endothelial cells, leading to atherosclerosis?

Oxidation by free radicals

How is shock-related injury caused?

Release of free radicals from phagocytes damaging membranes by lipid peroxidation

What protective effect do antioxidants have in shock-related injury?

Preventing leukotriene release from platelets and proteases release from macrophages

How are plant products used in the treatment of psoriasis and leukoderma related to free radicals?

Modulating the immune response to reduce free radical production

Study Notes

  • Free radicals are highly reactive molecules or fragments with unpaired electrons in their outer orbital.
  • They are continuously produced during normal metabolic processes, as well as in response to external stimuli such as oxygen radicals, light, or certain enzymes.
  • Reactive oxygen species (ROS) include superoxide anion radical (O2--), hydroperoxyl radical (HOO), hydrogen peroxide (H2O2), hydroxyl radical (OH), lipid peroxide radical (ROO), singlet oxygen (1O2), nitric oxide (NO), and peroxy nitrite (ONOO).
  • ROS can damage various tissues, including the membranes of cells, lipids, proteins, and DNA.
  • Free radicals can be produced by the body's own metabolic processes, such as in the electron transport chain, or by external factors like oxidizing agents, cigarette smoke, or air pollutants.
  • The body has various systems to scavenge and neutralize free radicals, including superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase, and glutathione reductase (GR).
  • Damage caused by free radicals can lead to various diseases and conditions, such as chronic inflammation, acute inflammation, respiratory diseases, eye diseases, reperfusion injury, atherosclerosis and myocardial infarction, shock-related injury, skin diseases, carcinogenesis, and aging.
  • Free radicals can damage DNA, leading to somatic mutations and malignancy.
  • Lipid peroxidation is a process by which free radicals damage lipids, leading to the formation of hydroperoxides and other damaging compounds.
  • Preventive anti-oxidants, such as catalase, glutathione peroxidase, and ethylene diamine tetra-acetate (EDTA), inhibit the initial production of free radicals.
  • Chain breaking anti-oxidants, such as superoxide dismutase, uric acid, vitamin E, and other compounds, can inhibit the propagation of free radical reactions.
  • Vitamin E is the primary lipid-soluble antioxidant, while vitamin C is the primary water-soluble antioxidant.
  • Other compounds, such as caffeine, cysteine, glutathione, and vitamin A, also have antioxidant properties.

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