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Summary of Biological Oxidation

COENZYME SYSTEM INVOLVED IN BIOLOGICAL OXIDATION
Biological oxidation is catalyzed by enzymes which function in combination with coenzymes and/or electron carrier proteins.

Different enzymes associated with biological oxidation are :
1. Oxidoreductases - These enzymes catalyse the removal of hydrogen from the substrate and add it to another substance, thus bringing about oxidation reduction reaction. Ex. Glyceraldehyde-3-Phosphate dehydrogenase.

2. Oxidases - These enzymes catalyse the removal of hydrogen from the substrate and add directly to the molecular oxygen. Ex. Cytochrome oxidases, tyrosinase, uricase.

3. Oxygenases - These enzymes incorporate oxygen into the substrates.
            (a) Mono - oxygenases - Adds only one atom of oxygen to the substrate. These are also known 
                 as mixed function oxidases.
            (b) Di - oxygenases - Adds both the atoms of oxygen to the substrate. Ex. Homogentisic acid di-
                 oxygenase.

4. Aerobic dehydrogenases - These enzymes remove hydrogen from the substrate and add it either directly to oxygen or any other artificial acceptors like methylene blue. The product formed is hydrogen peroxide.

5. Anaerobic dehydrogenases - These enzymes use other substrates or substances to donate the hydrogen. They transfer hydrogen’s to some other hydrogen acceptor, but not directly to oxygen. Thus the hydrogen acceptors are NAD, FAD and FMN. Heme proteins like cytochromes also receive hydrogen’s.
The cytochromes are ‘b’, ‘c1‘, ‘c’, ‘a’ and ‘a3‘.

6. Hydro peroxidases - These enzymes have either hydrogen peroxide (H2O2) or organic peroxide as their substrate.

Biological oxidation is the combination of oxidation-reduction transformations of substances in living organisms. Oxidation-reduction reactions are those which take place with a change in the oxidation state of atoms through the redistribution of electrons between them. [OR]

Biological oxidation is catalyzed by enzymes which function in combination with coenzymes and/or electron carrier proteins.

Free energy - A process will only happen spontaneously, without added energy, if it increases the entropy of the universe as a whole (or, in the limit of a reversible process, leaves it unchanged) – this is the Second Law of Thermodynamics. But to me at least, that's kind of an abstract idea. How can we make this idea more concrete and use it to figure out if a chemical reaction will take place ? 

Basically, we need some kind of metric that captures the effect of a reaction on the entropy of the universe, including both the reaction system and its surroundings. Conveniently, both of these factors are rolled into one convenient value called the Gibbs free energy

Endergonic and exergonic reactions
Reactions that have a negative ∆G release free energy and are called exergonic reactions. (Handy mnemonic: exergonic means energy is exiting the system.) A negative ∆G means that the reactants, or initial state, have more free energy than the products, or final state. Exergonic reactions are also called spontaneous reactions, because they can occur without the addition of energy.