Molecular Biology

What are Amino Acids



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Amino acids are biologically  significant compounds that are constituents of all proteins in the body.  There are 20 amino acids that form the building blocks of all proteins.  Each amino acid is composed of a CH group that to it attached an amino group and a carboxyl group in addition to an aliphatic chain that is characteristic for each and each amino acid. 


All 20 amino acids are chiral except for one amino acid which is glycine and is not chiral.  The bond between two amino acids is called a peptide bond.  It is formed when an amino group of one amino acid is attached to the carboxyl group of another amino acid.  Proteins are macromolecules that are composed of chains of amino acids that are connected with each other via peptide bonds. 


In the body part of the 20 amino acids are synthesized inside the tissues.  These amino acids are called non-essential amino acids.  Other amino acids are not synthesized in the body.  These amino acids must be given in the diet as a supplement to food.  Amino acids are a source of energy in the body to synthesize glucose in a process which is called gluconeogenesis. 


In this process glucose is synthesized rather than metabolized from various precursors.  Gluconeogenesis is an energy consuming process that requires many enzymes and ATP molecules.  Amino acids are usually deaminated in the liver to form ammonia molecules which is a lewis base that is toxic in high blood concentrations. 


In liver failure the process of ammonia detoxification and other toxic compounds detoxification is ceased due to the dysfunction of the liver.  Thus these toxic compounds can accumulate in the blood to high concentrations that can cause brain damage, a condition which is called hepatic encephalopathy. 


Ammonia which is the deamination product of amino acids metabolism has some benefits, in spite of its being toxic in high concentrations.  Ammonia can function as one of the available buffers in the body.  It can ameliorate acidosis of the blood. 


Amino acids besides its being important as building blocks for all proteins inside the body including the important class of proteins the enzymes have an additional function which is important to the body in general and for the nervous system in particular.  Some of the metabolites of amino acids can have significant role in the body physiology and homeostasis. 


Amino acids can function as neurotransmitters in the nervous system.  Glycine for example is an inhibitory amino acid in the nervous system.  Also there is a non-typical amino acid which is not incorportated  in the the usual structure of proteins and which is called gama aminobutyric acid or GABA.  Its function is an inhibitory neurotransmitter in the nervous system. 


It is the main inhibitory neurotransmitter that is known in the nervous system.  It has a relaxing effect on the body.  Agonists to GABA such as the drug xanax function by stimulating GABA receptors in the nervous system.  GABA's agonists are usually used to treat anxiety and panic conditions. 


In addition to this important neurotransmitter several other neurotransmitters exist which are important in modulating the function of the nervous system.  These also are derivatives of amino acids by certain modification in their structure that includes actions such as hydroxylation and decarboxylation using enzymatically catalyzed reactions.


The catecvholamines are derivatives of the amino acid tyrosine.  They include the neurotransmitters dopamine and epinephrine in addition to norepinephrine.  These neurotransmitters are obtained from the amino acid tyrosine by enzymatic reactions that lead to these compounds. 


Another neurotransmitter that is called serotonin is a derivative of the amino acid tryptophan.  Serotonin is an important neurotransmitter in the clinical condition of depression.  Its deficiency in the blood was found to be the culprit for the etiology of this disorder.  In addition patients of depression that were treated with serotonin agonists showed improvement from their depressive symptoms.

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