View source for The most important chemical reactions in metabolism

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The metabolic pathways of the human organism form an ''extensive network'' of interconnected reactions that often share ''common intermediates''. Chemical transformations of individual substances are usually classified according to a general mechanism common to all substances undergoing a given reaction. For example, ''decarboxylation''' is the '''splitting of CO<sub>2</sub> from the carboxyl group''', where the substrate may be different '''[[carboxylic acids]].''
===Alcohols, carbonyl compounds and carboxylic acids===
[[Alcohols and phenols| Alcohols]], [[Carbonyl compounds|carbonyl compounds]] and [[Carboxylic acids|carboxylic acids]] are important substrates for many reactions of metabolic pathways of organisms.


'''[[Alcohols and phenols| Alcohols]]''' contain the functional group '''−OH'''. Depending on the number of OH groups in the molecule, alcohols can be ''one-'', ''two-'' or ''polybasic''. Furthermore, depending on which carbon atom the OH group binds to, we distinguish between ''primary'', ''secondary'' and ''tertiary'' alcohols.
[[File:Alkoholy- primárny sekundárny terciarny.png|center|alcohols primary, secondary, tertiary]]
''Aldehydes''' with '''ketones''' form a group of ''carbonyl''' compounds. The functional group of aldehydes is the group '''−CHO''', in ketones '''−C=O'''.
Of this group of substances, the most important substrates are probably the reactions of [[Carboxylic acid|''' carboxylic acids]], characterized by the presence of the functional group ''−COOH''', and their '''derivatives''.
<gallery perrow="5">
File:Carbonsäure - Carboxylic acid.svg|carboxyl group
File:Aldehyde general structure.svg|alt=aldehyde group|Aldehyde group
File:Ketone-group-2D-skeletal.svg|ketone group
</gallery>

====Significant reactions of alcohols, aldehydes and carboxylic acids====
# Formation of anions and acyls derived from carboxylic acids
# Dehydrogenation and hydrogenation (oxidation and reduction)
# Esterification
[[File:Acile.PNG|thumb|Acile]]

===== Formation of anions and acyls derived from carboxylic acids=====
The carboxyl group is capable of ''dissociation''', with the degree of dissociation for individual acids given by  [[Theory of Acids and Bases|dissociation constant]]. Carboxylic acids are '''''weak''', which means that their dissociation is only partial. The acid thus gives rise to the ''anion''' (group''''' −COO<sup>−</sup>''').
After splitting off the whole −OH group from the carboxyl group, its '''acyl''' is formed.

===== Dehydrogenation and hydrogenation (oxidation and reduction)=====
During the chemical reaction, '''dehydrogenation'', the '''<nowiki/>''H is removed from the molecule'''. The obtained hydrogen can then be used for the formation of a proton gradient in mitochondria and for '''energy gain''' ([[ATP]]). '''The introduction of hydrogen''' into a molecule is called '''hydrogenation''. 
In the body, dehydrogenation and hydrogenation occur, for example, in the following processes:

:; Oxidation of single bonds to double bonds:
::::−CH 2−CH 2− {{return reaction}} −CH=CH− + 2 H<sup>+</sup> +<sub>2</sub> e<sup>−</sup><sub></sub>
::These reactions occur, for example, in [[Krebs cycle (FBLT)|''' Krebs cycle''']], at [[Β-oxidation|''' β-oxidation of fatty acids''']] or '''desaturation reactions''', which aim at the synthesis of unsaturated fatty acids.

:; Mutual conversion of alcohols, aldehydes / ketones and carboxylic acids
:: Alcohols, carbonyl compounds and carboxylic acids '' form a series'' differing from each other in the degree of oxidation / reduction. 
:: The general scheme of their mutual transformation is as follows (oxidation takes place towards the carbonyl compound and carboxylic acid, reduction in the opposite direction):
::::* '''Primary alcohol {{reversible reaction}} aldehyde {{reversible reaction}} carboxylic acid'''
:::::: R−CH<sub>2</sub>−OH {{return reaction}} R−CHO {{return reaction}} R−COOH
::::* '''Secondary alcohol {{reversible reaction}} ketone'''
:::::: R 1<sup></sup>−CH(OH)−R 2<sup></sup >{{return reaction}} R<sup>1</sup>−CO−R<sup>2</sup>
::::* '''Tertiary alcohol'''
:::::: "Slight" oxidation does not take place (it can be oxidized only with simultaneous splitting of the carbon chain).

An example of oxidation is the formation of ''dihydroxyacetone phosphate'' (DHA-P) from '''glycerol-3-phosphate''' (cofactor is [[FAD (flavin adenine dinucleotide)|''' FAD''']]), through which glycerol enters [[Glycolysis|glycolysis]] or [[Gluconeogenesis|gluconeogenesis]] according to the current needs of the organism.

===== Esterification=====
Esterification is the reaction of a carboxylic acid with an alcohol, producing an '''ester'' and '''water'':
[[File:Esterif 01.png|center|540px]]



===The most important carboxylic acids, their anions and acyls===
==== Saturated monocarboxylic acids====
{| class = wikitable
! C !! Systematic name!!   Trivial name!!  Latin name !! Acyl!!   Anion 
|--------------------------------------------------------------------------------------------------
| 1 || methane || ant ||  ''ac. formicum'' || formyl || formate
|--------------------------------------------------------------------------------------------------
| 2 ||	 Ethan || Vinegar ||  ''ac. aceticum'' || acetyl || acetate
|---------------------------------------------------------------------------------------------------
|3 || Propane || propionic || ''ac. propionicum'' || propionyl || propionate
|---------------------------------------------------------------------------------------------------
|4 ||	Butane || butter || ''ac. Butyricum'' || Butyryl || butyrate
|---------------------------------------------------------------------------------------------------
|5 || pentane ||  Valérová || ''ac. Valericum'' || Valeryl || valerate
|---------------------------------------------------------------------------------------------------
|12 || Dodecanese || Laurova || ''ac. Lauricum'' || Lauryl || laurate
|---------------------------------------------------------------------------------------------------
|16 || hexadecane || Palmito || ''ac. palmiticum'' || Palmitoyl || palmitate
|---------------------------------------------------------------------------------------------------
|18 || Octadecane ||  Stearova || ''ac. stearicum'' || stearoyl || Stearate
|}

==== Saturated dicarboxylic acids====
{| class = wikitable
! C !! Systematic name!! Trivial name!! Latin name !! Acyl!! Anion
|-----------------------------------------------------------------------------------------------
|2 ||	Etandi || Štavelová || ''ac. oxalicum'' || oxalyl ||  oxalate
|-----------------------------------------------------------------------------------------------
|3 ||	Propandiová || Malonova || ''ac. malonicum'' || Malonyl || malonate
|-----------------------------------------------------------------------------------------------
|4 ||	Butandi || amber || ''ac. succinicum'' ||  succinyl ||  succinate
|-----------------------------------------------------------------------------------------------
|5 ||	Pentondia || glutaric || ''ac. glutaricum'' || Glutaryl || glutarate
|-----------------------------------------------------------------------------------------------
|6 ||	hexandium || adip || ''ac. adipicum'' || Adipoyl || adipate
|}

==== Unsaturated monocarboxylic acids====
{| class = wikitable
! C               !! Systematic name!! Trivial name!! Latin name !! Acyl!! Anion
|----------------------------------------------------------------------------------------------------------------------------------------------------------
|18:1 || ''cis''-octadec-9-eno|| oil || ''ac. oleicum'' || oleoyl || oleate
|----------------------------------------------------------------------------------------------------------------------------------------------------------
|18:2 (ω−6) || ''cis'',cis''-octadeka-9,12-dienova || linoleic || ''ac. linoleicum'' || Linoloyl || linolate
|----------------------------------------------------------------------------------------------------------------------------------------------------------
|18:3 (ω−3) || ''cis'',cis'',cis''-octadeka-9,12,15-trienová || Linolenic || ''ac. linolenicum'' || Linolenoyl || Linolenate
|----------------------------------------------------------------------------------------------------------------------------------------------------------
|20:4 (ω−6) || ''cis'',''cis'',''cis'',''cis''-eikosa-5,8,11,14-tetraenová || arachidonová  || ''ac. arachidonicum'' || arachidonyl || arachidonát
|}

==== Unsaturated dicarboxylic acids====
{| class = wikitable
! C !! Systematic name!! Trivial name!! Latin name !! Acyl!! Anion
|-------------------------------------------------------------------------------------------------
|4 || ''cis''-butendi || Malein || ''ac. maleicum'' || Maleinyl || maleate
|-------------------------------------------------------------------------------------------------
|4 || ''trans''-butendi || Fumarova || ''ac. fumaricum'' || Fumaroyl || fumarate
|} 

==== Carboxylic acid derivatives====
{| class = wikitable
! C !! Systematic name!! Trivial name!! Latin name !! Acyl!! Anion 
|----------------------------------------------------------------------------------------------------------------------------
|3  || 2-oxopropane || pyrogrape || ''ac. pyruvicum'' || Pyruvyl || pyruvate
|----------------------------------------------------------------------------------------------------------------------------
|3  || 2-hydroxypropane || milk || ''ac. lacticum'' || lactoyl || lactate
|----------------------------------------------------------------------------------------------------------------------------
|4  || 3-oxobutaneous || acetoacetic ||                          || acetoacetyl || acetoacetate
|----------------------------------------------------------------------------------------------------------------------------
|4  || 3-hydroxybutane || β-hydroxybutyric ||                          ||                      || β-hydroxybutyrate
|----------------------------------------------------------------------------------------------------------------------------
|4  || 2-hydroxybutanedia || apple || ''ac. malicum'' || Maloyl || Malate
|----------------------------------------------------------------------------------------------------------------------------
|4  || 2-oxobutandium || oxaloacetic ||                          ||                      || oxaloacetate
|----------------------------------------------------------------------------------------------------------------------------
|5  ||  2-oxopentandia || α-ketoglutar ||                          || α-ketoglutaryl || α-ketoglutarate
|----------------------------------------------------------------------------------------------------------------------------
|6  || 2-hydroxypropane-1,2,3-tricarboxylic || lemon || ''ac. citricum'' ||                || citrate
|}


===Hydroxy acids and keto acids===
'''Hydroxy acids''' in addition to the −COOH group also contain the −OH group replacing one −H. 
'''Keto acids''' or '''oxo acids''' contain in the molecule in addition to the group −COOH also the group =O replacing one −H. 
Their mutual conversion is relatively common in metabolic pathways.

[[File:Keto-Enol-Tautomerie.png|right|280px]]
An example is the relatively common ''keto-enol tautomery'' in metabolism. It converts two forms of organic compounds:
* ''ketoform'' (or ''oxoform'') contains double-bonded oxygen as a group '''=O''',
* ''enolform'', which contains a double bond between carbons and one of them binds −OH group (i.e. contains the structure R<sup>1</sup>−CH=C(OH)−R<sup>2</sup>).
The mutual transformation of the two forms represents the '''migration of the hydrogen atom''' or the proton, accompanied by the '''swapping of the single bond''' and the adjacent '''double bond'''.


===Amino acids and oxo acids===
[[amino acids| Amino acids]] and oxo acids are substitution derivatives of carboxylic acids. Amino acids contain in the molecule in addition to the −COOH group also the group −NH 2, oxo acids group =O. Their mutual transformations are frequent in the organism, for example, there is a '''NH<sub>2</sub> group for group =O''' and vice versa.
[[File:Transaminace- transaminace.png|right|transamination]]
These transformations occur mainly in two processes:
:; Transamination
:: In this reaction, the amino acid is a donor −NH<sub>2</sub> of the oxo acid group. From the corresponding oxo acid, an amino acid is formed, and the original amino acid becomes an oxo acid:
::: AK1 + OxoK2 {{return reaction}} OxoK1 + AK2

:; Oxidative deamination
:: It is the formation of oxo acid from the amino acid '''by removing −NH<sub>2</sub> group'', which is released as '''ammonia (NH<sub>3</sub>)'''. Oxidative deamination is one of the important reactions through which amino acids initiate the process of their ''degradation'''. In the human body, they take place mainly in the liver, and the released ammonia is broken down in [[Urea cycle|''' urea synthesis''']].
::This reaction is mainly catalyzed by glutamate dehydrogenase.



===Decarboxylation and carboxylation===
Decarboxylation removes the carboxyl group, which is released as a '''CO<sub>2</sub>''' molecule and replaced by a proton. They are significant, for example, for
:* conversion of amino acids to ''biogenic amines'' (e.g. in the synthesis of many neurotransmitters),
:* dehydrogenation of 2-keto acids – pyruvate dehydrogenase reaction and two reactions of the Krebs cycle.

''Carboxylation''' is the opposite reaction, involving the introduction of a '''COOH'' group into the molecule. It occurs, for example, in
:* fatty acid synthesis,
:* [[Gluconeogenesis|gluconeogenesis]].

<noinclude>
[[Category:Biochemistry]]
[[Category:FBLT]]