Classification and Function of Amino Acids

Classification of amino acid

There are no any hard and fast rules for the classification of amino acids hence,different approaches can be used which are given as below:

A) On the basis of composition of side chain (ie; R group)

1) Simple amino acid :

Those amino acids which do not have functional group in their side chain .eg; Glycine ,Alanine,Valine,Leucine,and Isoleucine

2)Hydroxyl amino acid:

that amino acid which contains hydroxyl group (-OH) inside chain eg: Serine,and Threonine

3) Sulphur amino acid:

That amino acid which contains sulphur atom in their side chain .eg: Cysteine and Methionine

4)Acidic amino acid:

That amino acid which contains a carboxyl group in their side chain eg: Aspartic acid and Glutamic acid

5) Basic amino acid:

That amino acid which contains an amino group in the side chain eg; Lysine and Arginine.

fig: basic amino acid

6) Amino acid amides:

These are the derivatives of acidic amino acids in which one of the carboxyl group is transfered into an amide group (CO-NH₂) eg: Asparagine, Glutamine

7)Aromatic amino acid:Those amino acids which contain a benzene ring in the side chain.eg:Phenylalanine and tyrosine.

8) Heterocyclic amino acids:

Those amino acids which contain at least one atom other than carbon in their side chain eg;Proline,Histidine, and Tryptophan.

B) Based on number of amino acid and carboxylic group:

According to this basis amino acids can be categorized into 3 groups and this classification was given by Goldstein in 1976

1) Mono-amino -Monocarboxylic amino acids:

• Eg:Glycine,alanine,valine,isoleucine,leucine,proline,phenylalanine,Tyrosine,tryptophan,methionine,serine,threonine,cysteine,asparagine,glutamine

  2)Monoamine-Dicarboxylic:amino acids

  Eg:Aspartic acid,Glutamic acid.

  3) Diamino monocarboxylic amino acids

  Eg;lysine,arginine ,and histidine.

  C) Based on polarity of side chain:

  This is a meaningful classification of amino acids.According to this classification on the amino acids are categorised, into4 groups:

  Eg:glycine,alanine,valine,leucine,isoleucine,proline, phenylalanine,tryptophan and methionine.

  2)Amino acid with polar and uncharged side chain:

  Eg:serine,threonine,tyrosine,asparagine,cysteine,glutamine(CATTS)

  3) Amino acid with positive charge:

  Eg:lysine,arginine, and histidine

  4) Amino acid with negative charge:

  Eg; aspartic acid and glutamic acid.

  D) Based on nutritional requirement

  According to this basis is amino acids are categorised into 3 groups.

  1) Essential amino acids:

• The amino acids which are not synthesized by our body andutilised as growth promoting factors and must be taken in a diet are essential amino acids.Eg:tryptophan,threonine,lysine,leucine,isoleucine,methionine,valine,phenylalanine.(I2L2VPIM)

  2)Semi-essential amino acids

  Some amino acids which are partially synthesized by our body and utilised growth promoting factors mainly in growing children are semi-essential amino acids.eg:Arginine and histidine.

  3) Nonessential amino acids

  The amino acids which can be synthesized by our body are non-essential amino acids.Eg:Glycine,alanine,asparagine,glutamine.Tyrosine,aspartic acid,glutamic acid,serine,proline,cysteine.

  Peptide and polypeptide

  The amino acids are joint together in the protein by the condensation of alpha carboxylic group 1-amino acid with the alpha- the NH2 group of another amino acid and hence produce the primary structure of the protein chain.The bond between the two adjacent amino acid is called as peptide bond and thus formed is called peptide chain,

  

• Each peptide chain is of considerable length and may contain from 20-millions residue ,Depending upon the no.Of amino acids molecule composing chain, the peptide is termed as
  • dipeptide (containing two amino acid residue)
  • Tripeptide(containing 3 amino acid residue)

  If a peptide is made up of not more than 20amino acids it is called oligopeptide and if a peptide chain is made up of more than 20 amino acids residue than it is called polypeptide.The polypeptide if they contain more than 100 amino acids residue then they are called as the macro peptide.

  Representation of polypeptide chain

  During the representation of polypeptide chain in theN-terminal of the polypeptide chain is written to the left and the free C-terminal is written to the right.

  

• Functions of amino acids

  Aminoacid sare the chemical units or“building blocks”,as they are popularly called, that make up proteins.Amino acids contain about 16 percent nitrogen.Chemically,this is what distinguishes them from the other two basic nutrients,sugars and fatty acids,which do not contain nitrogen. To under and how vital amino acid are,we must understand and how essential proteins are to life.It is the protein that provides the structure for all living things.

  Supplemental amino acids are available in combination with various multi -vitamin formulas,as protein mixtures,in a wide variety of food supplements, and in a number of amino acid formulas. Each amino acid has specific functions in the body.The many functions and possible symptoms of deficiency of twenty-eight amino acids related compounds are described below

  a) Alanine:

• It aids in the metabolism of glucose, a simple carbohydrate that the body uses for energy.Epstein-Barr virus and chronic fatigue have been associated with excessive alanine levels and low levels of tyrosine and phenylalanine.One form of alanine, beta- alanine, is a constituent of pantothenic acid(vitamin65)and coenzyme A,a vital catalyst in the body.

  b) Arginine

  Arginineretardsthegrowthoftumoursamdcancerbyenhancingimmunefunction.Itincreasesthesizeandactivityofthethymusgland,whichmanufacturesTlymphocytes(T cells),crucialcomponentsofimmunesystem.ArgininemaybenifitthosesufferingfromAIDSandmaligantdiseasesthatsupressedtheimmunesystem.Itisalsousedinliverdisorderedlike cirrhosis of the liver and fatty liver, Seminal fluid contains arginine ,sexual maturity may be delayed by arginine deficiency.Conversely, arginine is useful in treating sterility in men., Arginine is important in muscle metabolism

  c)Asparagine: It is needed to maintain balance in the central nervous system. It prevents us from being either overly nervous or calm. It promotes the process by which one amino acid is transformed into another in the liver. This amino acid is mostly found in meat sources.

d)Aspartic acid; Because aspartic acid increases stamina , it is good for fatigue and plays a vital role in metabolism. Chronic fatigue may result from low levels of aspartic acid because this leads to lowered cellular energy.It is beneficial for neural and brain disorders.

e) Glutamic acid:

Glutamic acid is the excitatory neurotransmitter that increases the firing of neurons in the central nervous system.It is a major excitatory neurotransmitter in the brain and spinal cord and is the precursor of GABA. This amino acid is important in the metabolism of sugars and fats.and aids in the transportation of potassium across the blood-brain barrier.The glutamic acid is used as brain fuel. Glutamic acid helps to correct personality disorders and is used in the treatment of childhood behavioral disorders.

f)Glutamine:

glutamine is the most abundant free amino acid found in the muscles of the body. Because it can readily pass the blood -brain barrier ,it is known as brain fuel.In a brain, glutamine is converted into glutamic acid which is essential for cerebral function.

g) Valine:

Valine, an essential amino acid ,has a stimulant effect. It is needed for muscle metabolism, tissue repair,and the maintenance of a proper nitrogen balance in the body.Valine is found in high concentrations in muscle tissue. An excessively high level of valine may lead to such symptoms as a crawling sensation in the skin and even hallucinations.

h)Tyrosine:

Tyrosine is a precursor of the neurotransmitters norepinephrine and dopamine ,which regulate mood ,among other things. Tyrosine acts as a mood elevator , a lack of adequate amounts of tyrosine leads to a deficiency of norepinephrine in the brain, which in turns can result in depression.

Hence the amino acid is useful for the proper maintenance of body function.

References

Cassida, L.E Jr. Industrial microbiology. New age into publishers, 1996.

I, Stever. Biochemistry. new york: Wall freeman company, 1995.

JE, Smith. Biotechnology. Sinaeur Association, 2000.

Nelson, D L and M M Cox. Lihininger Principle of Biochemistry. Fifth. Freeman publication, 2004.