Biological oxidation: the essence of the process and its forms
Types and stages of biological oxidation
The living organisms of the planet cannot exist without energy. It is vital to every process and chemical reaction. Many living organism, including human beings, can receive energy from food. Let’s examine where energy comes from, and the reactions that take place at this time in the cells of living organisms.
The significance of biological oxidation and the history of how knowledge about it developed
At the basis of receiving energy lies the process of biological oxidation. This process has been studied in great detail, and there is even a whole science about it, biochemistry, which deals with all the subtleties and mechanisms of the process. 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.
Scientists first proposed the theory that complex chemical reactions took place inside each living organism in the 18th century. The problem was studied by the French chemist Antoine Lavoisier, who noticed that the processes of combustion and biological oxidation resembled each other.
The scientist traced the path of oxygen, which is absorbed by the living organism in the respiration process, and concluded that a process of oxidation took place in the organism, resembling the combustion process, but at a slower rate. Lavoisier discovered that molecules of oxygen, which is an oxidizer, interact with organic compounds (containing carbon and hydrogen), as a result of which their absolute transformation takes place, and the compounds break down.
Several aspects of the process remained unclear to scientists:
- why oxidation takes place at a low body temperature, unlike the similar combustion process;
- why the oxidation reaction is not accompanied by a flame and a large release of freed energy;
- how nutrients can “burn” in the organism of a living creature with a body that is around 80% water.
It took scientists many years to answer these and many other questions, and also to clarify what biological oxidation is. Chemists have now studied the connection of breathing with other metabolism processes, including the process of phosphorylation; the properties of enzymes that catalyze reactions of biological oxidation; localization of enzymes in the cell; and also the mechanism of the accumulation and transformation of energy.
Here you’ll find easy experiments for learning chemical properties of nutrients.
Biological oxidation and its forms
In different conditions, two types of biological oxidation can take place. Many fungi and microorganism receive energy by transforming nutrients by the anaerobic method. Anaerobic biological oxidation is a reaction that takes place without the presence of oxygen or its participation in the process in any way. This method of receiving energy is used by living organisms in an environment into which air does not enter – in clay, under the ground, in mud, in swamps, and in rotting substances. Anaerobic biological oxidation is called glycolysis.
The second, more complex method of transforming nutrients into energy is anaerobic biological oxidation, or tissue respiration. This reaction takes place in all aerobic organisms which use oxygen in the respiration process. The aerobic method of biological oxidation is impossible without molecular oxygen.
Paths of biological oxidation and participants of the process
In order to understand fully what the process of biological oxidation is, we should examine its stages.
Glycolysis is the oxygen-free splitting of monosaccharides, which precedes the process of cellular respiration and is accompanied by a release of energy. This stage is the initial one for every heterotrophic organism. After glycolysis, the fermentation process begins among anaerobes.
Oxidation of pyruvate — the process involves the transformation of pyruvic acid obtained in the glycolysis process into an acetyl coenzyme. The reaction takes place with the aid of the enzymic complex of pyruvate dehydrogenase. The localization is the mitochondrial cristae.
The breakdown of beta fatty acids — this reaction is carried out parallel with the oxidation of pyruvate in the mitochondrial cristae. The goal is to transform all fatty acids into acetyl coenzymes and deliver them to the cycle of tricarboxylic acids.
The Krebs cycle — first the acetyl coenzyme transforms into citric acid, then it is subjected to subsequent transformations: dehydration, decarboxylation and regeneration. All the processes repeat several times.
Oxidative phosphorylation is the final stage of the transformation in organisms of eukaryotic compounds. Adenosine diphosphate is transformed into adenosine triphosphoric acid. The energy required for this is supplied in the oxidation process of molecules of the dehydrogenase enzyme and of the dehydrogenase coenzyme formed in the previous stages. Then the energy is contained in the high-energy bonds of adenosine triphosphoric acid.
Oxidation of substances is carried out by the following methods:
- hydrogen is detached from the substrate which is being oxidized (dehydration process);
- the substrate gives up an electron;
- oxygen attaches to the substrate
In the cells of living organisms, all the above types of oxidation reactions are encountered, which are catalyzed by corresponding enzymes – oxidoreductases. The oxidation process does not take place in isolation, but is connected with the reduction reaction: combination reactions of hydrogen or electron take place simultaneously, i.e. oxidation-reduction reactions. The oxidation process is every chemical reaction that is accompanied by giving up electrons with an increase in oxidation states – the oxidized atom has a higher oxidation state. With the oxidation of a substance, reduction can also take place – electrons attach to the atoms of another substance.