Biological oxidation: the essence of the process and its forms

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.