REDOX REACTIONS IN COMMON SITUATIONS Hydrogenation could also be used instead of reduction in biochemistry and organic chemistry because it involves increasing the hydrogen number to the carbon atoms. When unsaturated fats become saturated with hydrogen atoms, this is reduction. When glucose gets broken down in to CO2, it is called oxidation. In organic chemistry, there can be the stepwise oxidation of a hydrocarbon, which starts as a hydrocarbon (fully reduced) and goes to make an alcohol, then an aldehyde or ketone, then a carboxylic acid, and finally a peroxide, which is highly oxidized. In metal chemistry, the rusting and corrosion of metals involve the oxidation of the metal to form a metal oxide, such as with iron (III) oxide, which is rust. Redox reactions are highly important in biological processes such as the entire process of cellular respiration, in which glucose, which is C6H12O6, is oxidized by oxygen to make CO2 and water. Of course, this does not depend on oxidation alone because oxygen gets reduced to form water. While photosynthesis is not the reverse of cellular respiration, it does involve the creation of glucose and oxygen from water and CO2 but it takes light energy to do this. The whole process of storing biological energy happens because of redox reactions. Energy substances like nicotinamide adenine dinucleotide or NAD+ get reduced to make things like NADH, which contributes greatly to the creation of a biological proton gradient, which helps to make adenosine triphosphate or ATP, which is the energy currency of all cellular organisms. A reduced biological substance in biological systems is one that has energy, while an oxidized biological substance has spent energy. Free radical reactions in biology are redox reactions in which free oxygen species are created in order to destroy pathogens by attaching electrons to any molecule in the pathogen. The problem is that these can build up and affect the human host, becoming dangerous if they do not attach to another redox molecule, such as an antioxidant. Antioxidants are, in effect, reducers that get rid of oxygen free radicals.
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