Before discussing antioxidants in detail, let’s define oxidation so we can understand it clearly.
Keywords: Human Physiology |General |Wellbeing| Self study| Cytochrome c oxidase |Flavoprotein—cytochrome system| Redox
Introduction
Oxidation and reduction go hand in hand; oxidation of one substance causes reduction of another. When one substance is oxidized, another substance gets reduced. We will learn oxidation and reduction in human physiology.
Oxidation
Oxidation is the addition of oxygen to a substrate or removing hydrogen or electrons from a substance.
Oxidation = substrate + oxygen
= substrate – hydrogen
= substrate – electron.
It is clear from its definition that oxygen is not essential for oxidation. Agree.
Reduction
Reduction is the removal of oxygen from a substrate or adding hydrogen or an electron to a substrate.
Reduction=substrate – oxygen
= substrate +hydrogen
= substrate + electron
In reduction, oxygen is not essential. Clear.
Anerobic oxidation
Dehydrogenation reaction is the removal of hydrogen from a substance, and this is common biological oxidation. Oxygen is not utilized; therefore, it is known as ‘Anerobic oxidation”.
Coenzyme S2 -2H
S-OH àS=O+2Hà
Coenzyme2H S2
S is oxidized, while S2 is reduced.
When a coenzyme accepts 2H, it gets reduced. The coenzyme transfers its hydrogen to another substance, say S2. Now, S2 is reduced.
NAD( nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate) are essential coenzymes; they accept hydrogen and get reduced.
Nicotinamide is a member of the B-complex vitamins. It is not synthesized in the human body and must be obtained from the diet.
Oxidation reactions that utilize oxygen:
1. Oxidation of phospho glyceraldehyde:
Oxidation
Phosphoglyceraldehyde Phosphoglyceric acid
It is a crucial step during glucose metabolism.
2. Oxidative decarboxylation:
Pyruvic acid –> ketoacid Acetyl CoA+ CO2
ATP is the energy coin of the cell. Cells use ATP during their activities and active processes. But cells can’t store ATP in large amounts. So, cells form ATP continuously.
ADP <==> ATP
Energy is transferred to ADP to form ATP. ATP provides its energy to the cell and becomes ADP.
ADP + inorganic phosphate àATP
Oxygen is required in this process. This is the primary process that forms ATP.
In another method, the phosphate group is added to ADP by the metabolic process; oxygen is not required.
In the mitochondria, ‘Respiratory chain oxidation’ or Oxidative phosphorylation occurs. Oxidation occurs by the ‘Flavoprotein—cytochrome system’ to form ATP. The ‘Flavoprotein—cytochrome system’ is a chain of enzymes that transfers hydrogen to oxygen to yield water.
At rest, 90% oxygen is consumed in the mitochondria to form ATP.
Respiratory chain oxidation consists of multiple enzymes. Each enzyme in the chain is reduced and reoxidized as the hydrogen is transferred to other enzymes. The hydrogen liberated from various substrates by dehydrogenase temporarily combines with coenzymes, such as NAD, NADP, and FAD.
Finally, the hydrogen is transferred to molecular oxygen to form water. The coenzyme is regenerated and becomes available for the following reaction. The final enzyme in the Respiratory chain oxidation is “cytochrome c oxidase.”
NAD.2H + ½ OxygenàNAD+ H2O + 3ATP
(several steps are involved).
FAD+ Cytochrome + Cytochrome c oxidase= ‘Flavoprotein -cytochrome system.”
The site of this reaction is the inner membrane of the mitochondria.
The coenzymes and flavin are reduced by adding two hydrogen atoms, while iron-containing cytochromes are reduced by electron transfer.
During the dehydrogenation reaction, a hydrogen atom is removed and undergoes acidic ionization to produce a proton (+v charge H+) and an electron(e—).
H < ==>H+ + e-
The total energy released during electron transport along the respiratory chain oxidation – is 40% ATP and 60% heat.
The cell fails to form ATP if oxygen is unavailable to the ‘Flavoprotein -cytochrome system.’
Redox
Redox was first used in 1928 (6) and is a portmanteau of reduction and oxidation. The process of oxidation is always accompanied by reduction. The two processes co-occur.
The oxidation is a half-reaction. Reduction is also a half-reaction. The two half-reactions occur together on every occasion to constitute a whole reaction.
When a reducing agent (reductant) loses electrons, it is oxidized, and the oxidizing agent(oxidant) gains electrons and is reduced.
A redox pair involves reducing and oxidizing agents engaged in a specific reaction.
FAQs:
Q1.Name few oxidizing agents.
A. Oxygen gas, halogens are few oxidizing agents to quote.
Q2.Name few reducing agents.
A. Hydrogen, oxalic acid and many reducing agents in our bodies.
Let us know your opinion









Leave a comment