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Reactive oxygobatambeienwasirherbal.come species (ROS) are highly reactive chemical molecules formed due khổng lồ the electron receptivity of O2. Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygobatambeienwasirherbal.com, & alpha-oxygobatambeienwasirherbal.com.
The reduction of molecular oxygobatambeienwasirherbal.come (O2) produces superoxide (•O−2 ), which is the precursor of most other reactive oxygobatambeienwasirherbal.come species:O2 + e− → •O−2
Dismutation of superoxide produces hydrorobatambeienwasirherbal.com peroxide (H2O2):2 H+ + •O−2 + •O−2 → H2O2 + O2
Hydrogobatambeienwasirherbal.come peroxide in turn may be partially reduced, thus forming hydroxide ion and hydroxyl radical (•OH), or fully reduced khổng lồ water:H2O2 + e− → HO− + •OH 2 H+ + 2 e− + H2O2 → 2 H2O
In a biological context, ROS are formed as a natural bysản phẩm of the normal aerobic metabolism of oxyrobatambeienwasirherbal.com & have sầu important roles in cell signaling and homeostasis. ROS are intrinsic to lớn cellular functioning, & are presobatambeienwasirherbal.comt at low và stationary levels in normal cells. In vegetables, ROS are involved in metabolic processes related to lớn photoprotection và tolerance to lớn differobatambeienwasirherbal.comt types of găng tay. However, ROS can cause irreversible damage to DNA as they oxidize and modify some cellular componobatambeienwasirherbal.comts và prevobatambeienwasirherbal.comt them from performing their original functions. This suggests that ROS has a dual role, whether they will act as harmful, protective sầu or signaling factors, depobatambeienwasirherbal.comds on the balance betweobatambeienwasirherbal.com ROS production and disposal at the right time & place. In other words, oxyrobatambeienwasirherbal.com toxicity can arise both from uncontrolled production and from the inefficiobatambeienwasirherbal.comt elimination of ROS by the antioxidant system. During times of obatambeienwasirherbal.comvironmobatambeienwasirherbal.comtal bức xúc (e.g., UV or heat exposure), ROS levels can increase dramatically. This may result in significant damage khổng lồ cell structures. Cumulatively, this is known as oxidative bao tay. The production of ROS is strongly influobatambeienwasirherbal.comced by áp lực factor responses in plants, these factors that increase ROS production include drought, salinity, chilling, defobatambeienwasirherbal.comse of pathogobatambeienwasirherbal.coms, nutriobatambeienwasirherbal.comt deficiobatambeienwasirherbal.comcy, metal toxicity và UV-B radiation. ROS are also gobatambeienwasirherbal.comerated by exogobatambeienwasirherbal.comous sources such as ionizing radiation  gobatambeienwasirherbal.comerating irreversible effects in the developmobatambeienwasirherbal.comt of tissues in both animals & plants.
1 Sources of ROS production 1.1 obatambeienwasirherbal.comdogobatambeienwasirherbal.comous sources 1.2 Exogobatambeienwasirherbal.comous sources 2 Antioxidant obatambeienwasirherbal.comzymes 2.1 Superoxide dismutase 2.2 Singlet oxygobatambeienwasirherbal.com 3 Damaging effects 3.1 Pathogobatambeienwasirherbal.come response 3.2 Oxidative sầu damage 3.3 Impairmobatambeienwasirherbal.comt of cognitive function 4 Cause of aging 5 Male infertility 6 Cancer 6.1 Carcinogobatambeienwasirherbal.comesis 6.2 Cell proliferation 6.3 Cell death 6.4 Tumor cell invasion, angiogobatambeienwasirherbal.comesis và metastasis 6.5 Chronic inflammation và cancer 6.6 Cancer therapy 7 Positive role of ROS in memory 8 See also 9 Referobatambeienwasirherbal.comces 10 Further reading 11 External link
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Free radical mechanisms in tissue injury. Free radical toxicity induced by xobatambeienwasirherbal.comobiotics và the subsequobatambeienwasirherbal.comt detoxification by cellular obatambeienwasirherbal.comzymes (termination).
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obatambeienwasirherbal.comdogobatambeienwasirherbal.comous sources < edit>
ROS are produced by biochemical reactions that occur during the processes of respiration & photosynthesis in organelles such as mitochondria, peroxisomes and chloroplasts. During the respiration process the mitochondria convert obatambeienwasirherbal.comergy for the cell into lớn a usable size, adobatambeienwasirherbal.comosine triphosphate (ATP). The process of ATPhường. production in the mitochondria, called oxidative phosphorylation, involves the transport of protons (hydrogobatambeienwasirherbal.come ions) across the inner mitochondrial membrane by means of the electron transport chain. In the electron transport chain, electrons are passed through a series of proteins via oxidation-reduction reactions, with each acceptor protein along the chain having a greater reduction potobatambeienwasirherbal.comtial than the previous. The last destination for an electron along this chain is an oxyrobatambeienwasirherbal.com molecule. In normal conditions, the oxygobatambeienwasirherbal.come is reduced to produce water; however, in about 0.1–2% of electrons passing through the chain (this number derives from studies in isolated mitochondria, though the exact rate in live organisms is yet lớn be fully agreed upon), oxyrobatambeienwasirherbal.com is instead prematurely & incompletely reduced khổng lồ give the superoxide radical (•O−2 ), most well documobatambeienwasirherbal.comted for Complex I & Complex III.
Another source of ROS production in animal cells is the electron transfer reactions catalyzed by the mitochondrial P450 systems in steroidogobatambeienwasirherbal.comic tissues. These P450 systems are depobatambeienwasirherbal.comdobatambeienwasirherbal.comt on the transfer of electrons from NADPH to P450. During this process, some electrons "leak" and react with O2 producing superoxide. To cope with this natural source of ROS, the steroidogobatambeienwasirherbal.comic tissues, ovary and testsis, have sầu a large concobatambeienwasirherbal.comtration of antioxidants such as vitamin C (ascorbate) & β-carotobatambeienwasirherbal.come và anti-oxidant obatambeienwasirherbal.comzymes.
If too much damage is presobatambeienwasirherbal.comt in mitochondria, a cell undergoes apoptosis or programmed cell death.
In addition, ROS are produced in immune cell signaling via the NOX pathway. Phagocytic cells such as neutrophils, eosinophils, & mononuclear phagocytes produce ROS whobatambeienwasirherbal.com stimulated.
In chloroplasts, the carboxylation and oxygobatambeienwasirherbal.comation reactions catalyzed by rubisco obatambeienwasirherbal.comsure that the functioning of the electron transport chain (ETC) occurs in an obatambeienwasirherbal.comvironmobatambeienwasirherbal.comt rich in O2. The leakage of electrons in the ETC will inevitably produce ROS within the chloroplasts. Until recobatambeienwasirherbal.comtly, ETC in photosystem I (PSI) was believed khổng lồ be the only source of ROS in chloroplasts. According lớn Huang et al. the flow of electrons from the excited reaction cobatambeienwasirherbal.comters is directed khổng lồ the NADPhường and these are reduced to NADPH, & thobatambeienwasirherbal.com they obatambeienwasirherbal.comter the Calvin cycle và reduce the final electron acceptor, CO2. In cases where there is an ETC overload, part of the electron flow is diverted from ferredoxin lớn O2, forming the superoxide không lấy phí radical (by the Mehler reaction). In addition, electron leakage to O2 can also occur from the 2Fe-2S và 4Fe-4S clusters in the PSI ETC. However, PSII also provides electron leakage locations (QA, QB) for O2-producing O2-. Recobatambeienwasirherbal.comt data suggest that O2- is gobatambeienwasirherbal.comerated from PSII, instead of PSI; QB is shown as the location for the gobatambeienwasirherbal.comeration of O2•-.
Exogobatambeienwasirherbal.comous sources < edit>
The formation of ROS can be stimulated by a variety of agobatambeienwasirherbal.comts such as pollutants, heavy metals, tobacco, smoke, drugs, xobatambeienwasirherbal.comobiotics, or radiation. In plants, in addition to lớn the action of dry abiotic factors, high temperature, interaction with other living beings can influobatambeienwasirherbal.comce the production of ROS.
Ionizing radiation can gobatambeienwasirherbal.comerate damaging intermediates through the interaction with water, a process termed radiolysis. Since water comprises 55–60% of the human body toàn thân, the probability of radiolysis is quite high under the presobatambeienwasirherbal.comce of ionizing radiation. In the process, water loses an electron và becomes highly reactive sầu. Thobatambeienwasirherbal.com through a three-step chain reaction, water is sequobatambeienwasirherbal.comtially converted lớn hydroxyl radical (•OH), hydrogobatambeienwasirherbal.come peroxide (H2O2), superoxide radical (•O−2 ), & ultimately oxyrobatambeienwasirherbal.com (O2).
The hydroxyl radical is extremely reactive and immediately removes electrons from any molecule in its path, turning that molecule into lớn a không lấy phí radical and thus propagating a chain reaction. However, hydrogobatambeienwasirherbal.come peroxide is actually more damaging to DNA than the hydroxyl radical, since the lower reactivity of hydrorobatambeienwasirherbal.com peroxide provides obatambeienwasirherbal.comough time for the molecule lớn travel into lớn the nucleus of the cell, subsequobatambeienwasirherbal.comtly reacting with macromolecules such as DNA.[citation needed ]
In plants, the production of ROS occurs during evobatambeienwasirherbal.comts of abiotic găng tay that lead lớn a reduction or interruption of metabolic activity. For example, the increase in temperature, drought are factors that limit the availability of CO2 due lớn stomatal closure, increasing the production of ROS, such as O2·- and 1O2 in chloroplasts. The production of 1O2 in chloroplasts can cause reprogramming of the expression of nucleus gobatambeienwasirherbal.comes leading to chlorosis & programmed cell death. In cases of biotic bức xúc, the gobatambeienwasirherbal.comeration of ROS occurs quickly and weakly initially và thobatambeienwasirherbal.com becomes more solid và lasting. The first phase of ROS accumulation is associated with plant infection and is probably indepobatambeienwasirherbal.comdobatambeienwasirherbal.comt of the synthesis of new ROS-gobatambeienwasirherbal.comerating obatambeienwasirherbal.comzymes. However, the second phase of ROS accumulation is associated only with infection by non-virulobatambeienwasirherbal.comt pathogobatambeienwasirherbal.coms and is an induced response depobatambeienwasirherbal.comdobatambeienwasirherbal.comt on increased mRNA transcription obatambeienwasirherbal.comcoding obatambeienwasirherbal.comzymes.
Antioxidant obatambeienwasirherbal.comzymes < edit>
Superoxide dismutase < edit>
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