Oxidative Stress and Reactive Oxygen Species

An atom or molecule with an unpaired electron in its outer orbital.

A molecule or atom gains oxygen.

A molecule or atom loses oxygen.

A substance that accepts electrons, causing another molecule to be oxidized.

A substance that donates electrons, causing another molecule to be reduced.

A reaction in which a covalent bond breaks, with each resulting atom getting one of the shared electrons.

Free radicals are highly reactive due to their unpaired electron, so they quickly react with other molecules.

Free radicals can cause chain reactions, leading to the formation of more free radicals.

Hydrogen peroxide (H2O2) indirectly damages DNA by generating a highly reactive molecule called the hydroxyl radical (OH-) in the presence of transition metal ions. It does not directly interact with DNA itself.

Hydrogen peroxide is a small molecule that readily passes through cell membranes, unlike superoxide. This allows it to travel to different cellular locations and decompose, generating hydroxyl radicals.

The hydroxyl radical (OH.) is a highly reactive species due to its unpaired electron. It can damage DNA by abstracting hydrogen atoms, adding to molecules, or transferring electrons.

Ionizing radiation can break the O-H bond in water molecules, creating hydroxyl radicals. This happens when high-energy radiation interacts with water.

The Haber-Weiss reaction involves the interaction of superoxide (O2-) and hydrogen peroxide (H2O2) to produce the hydroxyl radical (OH-) non-enzymatically. It is a significant source of hydroxyl radicals in biological systems.

The Fenton reaction produces hydroxyl radicals by combining hydrogen peroxide with iron (Fe2+) or copper (Cu2+) ions. It is a critical pathway for the generation of hydroxyl radicals in biological systems.

Nitric oxide (NO) can react with superoxide (O2-) to produce peroxynitrite, which then readily decomposes into a hydroxyl radical (OH.) and a nitrogen dioxide radical (NO2.). This pathway is another source of hydroxyl radicals in cells.

Singlet oxygen (1O2) is an excited state of molecular oxygen. It is chemically reactive and can participate in reactions like lipid peroxidation, damaging cell membranes.

A type of signaling pathway within cells that is activated by growth factors and cytokines, leading to the production of Reactive Oxygen Species (ROS).

Reactive Oxygen Species (ROS) are molecules containing oxygen that are highly reactive, often damaging cells. They are produced by various cellular processes, including growth factor receptor signaling.

A group of proteins that act as tumor suppressors, meaning they can help prevent the uncontrolled growth of cancer cells. One key function is to regulate cell cycle and apoptosis.

A process where cells self-destruct in a controlled manner, important for removing damaged or unwanted cells. Oxidative stress can trigger apoptosis.

A process that damages lipids, particularly those in cell membranes. It often involves the interaction of reactive oxygen species with metal ions, producing harmful byproducts.

The initial step in lipid peroxidation where a free radical, typically a hydroxyl radical, removes a hydrogen atom from a fatty acid, creating a reactive fatty acid radical.

A chain reaction where the initial fatty acid radical reacts with oxygen, forming a peroxyl radical. This unstable radical then steals a hydrogen atom from another fatty acid, creating a new radical and a hydroperoxide.

The process of stopping the radical chain reaction in lipid peroxidation. It occurs when two radicals react to form a non-radical species.

A type of molecule that helps to neutralize free radicals, protecting cell membranes from oxidative damage.

Molecules that contain multiple double bonds, making them more susceptible to lipid peroxidation because they have reactive hydrogen atoms.

The product of lipid peroxidation, a molecule that contains an oxygen-oxygen bond and can further contribute to oxidative damage.

The irreversible oxidation of amino acids often results in the formation of hydroxylated and carbonylated derivatives. These modifications occur due to the attack of reactive oxygen species on the amino acid side chains.

Dityrosine is formed through the cross-linking of tyrosine residues, a result of side chain oxidation. This modification can alter protein structure and function.

Protein carbonylation is a process where carbonyl groups are added to proteins, potentially altering their structure and function. This process occurs through direct attack of reactive oxygen species on amino acid side chains or through the addition of reactive aldehydes.

Metal cofactors like iron can enhance oxidative degradation of proteins by facilitating the Fenton reaction. In this reaction, hydrogen peroxide is converted to a hydroxyl radical, which then oxidizes amino acid residues, often at the metal binding site.

The accumulation of damaged proteins can lead to competition with their functional active counterparts, potentially disrupting cellular processes. Further, the formation of protein aggregates can contribute to cell death.

Oxidative modification of specific amino acids can serve as a signal for proteolysis, targeting these damaged proteins for degradation by specific proteases. This process helps to remove damaged proteins and maintain cellular integrity.

Various types of proteases, including cysteine, serine, aspartate proteases, and metalloproteases, can break down oxidized proteins. These enzymes contribute to the removal of damaged proteins and maintain cellular homeostasis.

Oxidative damage to DNA occurs through the action of reactive oxygen species and other oxidizing agents, leading to various lesions including base degradation, single or double strand breaks, and cross-linking to proteins.

Reactive oxygen species (ROS) are molecules containing oxygen that can damage cells. They can act as secondary messengers in signaling pathways, but also trigger aging and cell death.

ROS can have both beneficial and harmful effects on cells. They can promote or inhibit tumor growth depending on concentration and cellular context.

Antioxidants are molecules that can reduce the damaging effects of reactive oxygen species by donating electrons or breaking chain reactions.

Antioxidants help protect cells from oxidative stress. They can be categorized as enzymatic or non-enzymatic, each with different mechanisms.

Enzymatic antioxidants are proteins that catalyze reactions to neutralize reactive oxygen species. Superoxide dismutase, catalase, and glutathione peroxidase are examples.

Non-enzymatic antioxidants are molecules that directly react with ROS. They can be nutrients like vitamins C & E, or metabolic products like glutathione.

Superoxide dismutase (SOD) is an enzyme that catalyzes the breakdown of superoxide into oxygen and hydrogen peroxide. It plays a crucial role in protecting cells from oxidative stress.

Catalase is an enzyme responsible for breaking down hydrogen peroxide into water and oxygen. It plays an essential role in protecting cells from damage by this reactive molecule.