Which chemical reactions are considered the most important?

We should state right away that this ques­tion is very much a rhetor­i­cal one (i.e. one to which you can spend an end­less amount of time look­ing for an an­swer, with­out ever find­ing one). How­ev­er, we can still try to an­swer it, by stat­ing that the most im­por­tant re­ac­tions in the world are the ones that are re­spon­si­ble for life on earth. They all take place in the or­gan­isms of liv­ing crea­tures. They in­clude the fol­low­ing pro­cess­es (note that they are not re­ac­tions, but pro­cess­es, each one of which in­volves an enor­mous num­ber of the most var­ied re­ac­tions):

1. Pho­to­syn­the­sis
2. Res­pi­ra­tion – cel­lu­lar and non-cel­lu­lar
3. Biosyn­the­sis of pro­tein
4. Hy­drol­y­sis
5. Fer­men­ta­tive pro­cess­es

Again, we should clar­i­fy that any re­ac­tion that takes place in a liv­ing or­gan­ism is im­por­tant, but in the ab­sence of just one of the pro­cess­es list­ed above, life on the plan­et would be im­pos­si­ble. Let’s ex­am­ine these pro­cess­es in more de­tail.

Pho­to­syn­the­sis

This process takes place in plant cells, and its sum­ma­ry re­ac­tion is the fol­low­ing: in the in­ter­ac­tion of wa­ter and car­bon diox­ide un­der the im­pact of a huge quan­ti­ty of fer­men­ta­tive sys­tems, the syn­the­sis of glu­cose takes place and oxy­gen is re­leased. In bi­ol­o­gy text­books for the 10th grade this process is de­scribed as fol­lows:

СO₂ + Н₂O = C₆H₁₂O₆ + O₂

This equa­tion can­not be called ac­cu­rate, as it does not take into ac­count all of the com­plex bio­chem­i­cal re­ac­tions which cause the re­ac­tion to pro­ceed in the way it does. Just think, if you mix car­bon diox­ide with wa­ter with­out cre­at­ing spe­cial con­di­tions that are only pos­si­ble in a liv­ing or­gan­ism, you won’t get any­thing more than fizzy wa­ter. Ad­di­tion­al­ly, even with the par­tic­i­pa­tion of spe­cial fer­ments, glu­cose is not the only prod­uct of re­ac­tion – oth­er or­gan­ic sub­stances also form, most of which are car­bo­hy­drates. How­ev­er, for il­lus­tra­tive pur­pos­es this equa­tion can be used – cal­cu­la­tions can be car­ried out with it.

It is dif­fi­cult to un­der­es­ti­mate how use­ful this re­ac­tion is – both glu­cose and oxy­gen (a side prod­uct of re­ac­tion, by the way) have fun­da­men­tal im­por­tance. If glu­cose is re­quired for a plant to pro­vide en­er­gy ex­change in cells, oxy­gen is re­quired by all liv­ing or­gan­isms which in­hab­it our plan­et (with the ex­cep­tion of anaer­obes – or­gan­ism which live and mul­ti­ply in an oxy­gen-free en­vi­ron­ment). Ad­di­tion­al­ly, in this re­ac­tion the con­cen­tra­tion of car­bon diox­ide on the plan­et drops, which is also a very good thing. De­struc­tion of plant life leads to a de­crease in pho­to­syn­the­sis – and in its turn, this caus­es the green­house ef­fect to de­vel­op.

Res­pi­ra­tion

Res­pi­ra­tion – what is this process from the point of view of chem­istry? In the tra­di­tion­al un­der­stand­ing, the res­pi­ra­tion process sim­ple in­volves the con­sump­tion of oxy­gen and the re­lease of car­bon diox­ide. This is es­sen­tial­ly cor­rect to a cer­tain ex­tent, but this de­scrip­tion is high­ly ab­stract and im­pre­cise – it ig­nores a huge amount of fun­da­men­tal­ly im­por­tant bio­chem­i­cal pro­cess­es.

We must also sep­a­rate the con­cepts of ex­ter­nal and cel­lu­lar res­pi­ra­tion. The gaseous ex­change be­tween the hu­man body and the en­vi­ron­ment is ex­ter­nal res­pi­ra­tion, while cel­lu­lar res­pi­ra­tion is the sum of an enor­mous num­ber of re­ac­tions, which take place both in the pres­ence of oxy­gen and with­out it. In any case, the goal of this res­pi­ra­tion process is to re­ceive en­er­gy, which cu­mu­lates in macro-en­er­gy bonds of adeno­sine phos­phor­ic acid (this com­pound is called ATP for short).

The process of in­ner res­pi­ra­tion can be pre­sent­ed as fol­lows: First stage – oxy­gen-free, or gly­col­y­sis – from one glu­cose mol­e­cule, two mol­e­cules of ARP and lac­tic acid are formed. The sec­ond stage is with oxy­gen, where the split­ting of lac­tic acid (syn­the­sized dur­ing gly­col­y­sis) caus­es 36 mol­e­cules of ATP to be formed. It is log­i­cal to as­sume that with­out en­er­gy, the hu­man body would not func­tion – so oxy­gen is a vi­tal el­e­ment to life.

Biosyn­the­sis of pro­tein

All high­er an­i­mals are es­sen­tial­ly made of pro­tein – a poly­mer which in its turn con­sists of a large amount of amino acids. The syn­the­sis of pro­teins in­cludes a huge amount of re­ac­tions which takes place thanks to ri­bo­somes, mRNA and tRNA. This can be il­lus­trat­ed in the fol­low­ing way – thanks to dif­fer­ent types of ri­bonu­cle­ic acids, amino acids are trans­port­ed to ri­bo­somes, with the sub­se­quent at­tach­ment of monomers to the pro­tein mol­e­cule. So if this process be­comes im­pos­si­ble for some rea­son, the cre­ation of liv­ing or­gan­isms will not be pos­si­ble.

Click here to find chem­i­cal ex­per­i­ments for learn­ing prop­er­ties of pro­tein.

Hy­drol­y­sis

This process in­volves the dis­so­ci­a­tion (break­down) of com­plex mol­e­cules or ion­ic struc­tures un­der the im­pact of wa­ter (it of­ten takes place with the for­ma­tion of new sub­stances). To ex­am­ine this process in the con­text of the ar­ti­cle, we should note that the ini­tial stages of di­ges­tion are also hy­drol­y­sis.

It takes place as fol­lows: in most cas­es, or­gan­ic com­pounds en­ter the hu­man body – starch, cel­lu­lose, pro­teins, glyc­erin and high­er fat­ty acids, but only monomers are ab­sorbed in the in­tes­tine (if poly­mers were present be­fore the di­ges­tion process). So we can see that for the di­ges­tion process to take place nor­mal­ly, it must be sup­plied with monomer­ic com­pounds.

With­out the hy­drol­y­sis process with the split­ting of com­plex com­pounds, this would be im­pos­si­ble.

Fer­men­ta­tive pro­cess­es

With­out bi­o­log­i­cal cat­a­lysts known as en­zymes, any meta­bol­ic process would take place a hun­dred or a thou­sand times more slow­ly – the me­tab­o­lism would slow down enor­mous­ly. But with en­zymes (if they dis­play nor­mal ac­tiv­i­ty) ev­ery­thing takes place pre­cise­ly and with­in set time­frames.

Con­clu­sion

All chem­i­cal re­ac­tions are sig­nif­i­cant, but the ones in these ex­am­ples are vi­tal to main­tain life on earth. The en­tire or­gan­ism re­lies on them!