Reactive Oxygen Species in Cellular Injury

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Questions and Answers

What role does NADPH oxidase play in the respiratory burst mechanism?

It produces nitric oxide for antimicrobial activity.

It facilitates the production of superoxide from NADPH. (correct)

It generates hydroxyl radicals from hydrogen peroxide.

It converts O2 into H2O.

Which compound is transformed into HOCl by myeloperoxidase in the presence of a halide?

Hydrogen peroxide (correct)

H2O

Superoxide

Nitric oxide

What term describes the imbalance between free radical generation and their scavenging?

Oxidative stress (correct)

Oxidative damage

Free radical overload

Cellular instability

What is the primary function of HOCl produced by myeloperoxidase?

To act as an antimicrobial agent. Signup and view all the answers

Which of the following is a primary source of endogenous reactive oxygen species (ROS) in cells?

Mitochondria Signup and view all the answers

What is the initial product of the Haber-Weiss reaction involving hydrogen peroxide and superoxide?

Hydroxyl radicals Signup and view all the answers

Which cellular component can be damaged by lipid peroxidation due to free radicals?

All of the above Signup and view all the answers

In the Haber-Weiss reaction, what role do iron ions play?

They facilitate the generation of hydroxyl radicals. Signup and view all the answers

What is a potential consequence of the release of enzymes from damaged lysosomal membranes?

Cell death Signup and view all the answers

Which of the following statements about nitric oxide synthase (NOS) is accurate?

It produces nitric oxide alongside peroxynitrite. Signup and view all the answers

Free radicals are particularly reactive due to their having:

An unpaired electron Signup and view all the answers

What occurs during the Fenton reaction following the Haber-Weiss reaction?

Fe2+ converts into ferric ions. Signup and view all the answers

What phenomenon occurs as a result of restoring blood flow to ischemic tissues?

Reperfusion injury Signup and view all the answers

What is the end result of the net reaction between superoxide and hydrogen peroxide in the Haber-Weiss mechanism?

Hydroxyl radicals and oxygen are generated. Signup and view all the answers

What type of fatty acids are primarily affected by ROS-induced peroxidation?

Polyunsaturated fatty acids Signup and view all the answers

Activation of proteases results in disruption of which cellular structure?

Cytoskeleton Signup and view all the answers

Study Notes

Reactive Oxygen Species (ROS) in Cellular Injury

Several molecules are generated during cellular injury, damaging membranes, proteins, and nucleic acids.
Cells have inherent antioxidant compounds to limit damage.
Cellular injury from ROS occurs when these defense mechanisms are overwhelmed.

Free Radicals

Free radicals are chemical compounds with a single unpaired electron.
Highly reactive and interact with adjacent molecules, releasing energy and altering them.
Interact with lipids in cell membranes (peroxidation), proteins, and DNA, leading to damage.
Lipid peroxidation is a chain reaction damaging cell membranes and causing further oxidation of membrane components.
This imbalance between free radical generation and scavenging is called oxidative stress.

Mechanism of ROS

Mitochondria are the primary source of endogenous reactive oxygen species (ROS).
Excessive ROS production damages macromolecules (nucleic acids, proteins, and lipids).
This leads to tissue damage in chronic/degenerative diseases.
ROS further damages structures through lipid peroxidation.
Activation of proteases disrupts the cytoskeleton, damaging cell structure.
Disruption of lysosomal membranes releases damaging enzymes (e.g., DNAses, proteases), leading to cell death.

Reactive Oxygen Species Involvement in Cell Damage

Mitochondria are the primary cellular source of reactive oxygen species.
ROS can damage cell membranes, proteins, and DNA
Imbalance between ROS production and scavenging is called oxidative stress and causes damage.
ROS damage can involve inflammation, reperfusion injuries, altered metabolism, and exposure to exogenous chemicals or ionizing radiation.
Damage may include lipid peroxidation, protein oxidation/cross-linking, and DNA strand breaks.

Sources of ROS Damage

Mitochondria are the primary source of ROS in the cell.
Other sources include: inflammation, reperfusion injury, altered metabolism, chemical exposure, and ionizing radiation.

Cellular Defense Mechanisms

Cells have antioxidant compounds to mitigate ROS damage.
Important enzymes involved in neutralizing ROS include superoxide dismutase (SOD), catalase, and glutathione peroxidase.
Vitamins C, E, and carotenoids act as antioxidants.

Protective Mechanisms

Cells have protective mechanisms against ROS-mediated injury.
These include enzymes like superoxide dismutase (SOD), catalase, and glutathione peroxidase.
They neutralize damaging ROS, thereby preventing severe injury.
Other protective factors include vitamins E and C and antioxidants in the diet.

Important Enzymes in Respiratory Burst

NADPH oxidase is present in phagosomes (membrane-bound compartments).
Along with NADPH, it uses oxygen to generate superoxide anions and hydrogen peroxide (H₂O₂).
These oxygen metabolites are crucial for killing bacteria during the respiratory burst.
Other key factors in the respiratory burst are oxygen, NADPH, NADP, and HMP shunt.

Cellular Structures Involved in ROS Neutralization

Peroxisomes contain catalase, which neutralizes hydrogen peroxide.
Mitochondria, cytosol, and peroxisomes contain important enzymes for ROS neutralization.

Additional Notes:

The Haber-Weiss reaction is a cellular reaction producing hydroxyl radicals from hydrogen peroxide and superoxide, catalyzed by iron ions
Reactive oxygen species are crucial in immune responses to bacteria.

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Description

This quiz explores the role of reactive oxygen species (ROS) in cellular injury. It covers their formation, mechanisms, and the impact of oxidative stress on cellular components such as lipids, proteins, and nucleic acids. Understand the delicate balance between free radicals and antioxidant defenses.