There are twenty amino acids (AA) which have been found to occur in all proteins and for which genetic codon exits. Each of these has one or more genetic codon which is present within the molecule of specific messenger RNA which themselves is produced under the direction of a gene occurring in DNA molecules. DNA is a sequence of four nucleotides namely, adenine, guanine, cytosine, and thymine. Their exact sequence determines genetic codon. Each set of three nucleotides in the DNA codes for one amino acid attached to one another. These are arranged in 64 different combinations, more than enough to code 20 amino acids. Out of 64 codons, there are three codon UAA, UAG, and UGA which do not code for any amino acid and hence are known as a stop codon. Every gene starts with initiation codon AUG which encode the AA methionine. In this way, amino acids are playing an essential role within DNA molecule and also helpful in its synthesis by manufacturing purines and pyrimidines e.g. alanine, serine, aspartic acid etc.
Amino acids needed by the human body
Amino acids needed by the human body are essential elements of our diet. These are basically proteins which are one of the basic nutrients needed to maintain the body’s health. About three-quarters of the body solids are proteins. These include structural protein, enzyme nucleoproteins, proteins that transport oxygen, proteins of muscles that cause muscles contraction and many other types that perform specific intracellular and extracellular functions throughout the body. The amino acids needed by our body are essential amino acids and they must be provided by food and they include histidine, leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
Physiological functions of some of the individual amino acids in our body both essential and non-essential:
Histidine amino acid
- Is required in our body since it is the important precursor of histamine.
Valine, leucine and Isoleucine amino acids
- These result in the formation of elements necessary for the citric acid cycle.
- The error in metabolism of these gives rise to Maple syrup Urine diseases.
Methionine amino acid
- It is converted into S-adenosylmethionine which acts as a methyl donor and results in the formation of adrenaline.
Phenylalanine and Tyrosine amino acids
- Are used to make the neurotransmitter norepinephrine and epinephrine, which relay nervous system messages throughout the body.
- They can also be used to make melanin pigment which is responsible for hair, eyes, and skin color.
- They also make thyroxin, which helps to regulate the metabolic rate.
Glycine amino acid
- It is the part of the molecule of glutathione which is a coenzyme in many biochemical reactions and helps in maintenance of cell integrity by protecting hemoglobin, catalase, and lipoproteins of the cell membrane.
- It takes part in the syntheses of heme, purines, and creatine.
- It performs detoxicating reaction by conjugating with benzoic acid in the liver to form hippuric acid which is then excreted in the urine.
- It has a very important neurotransmitter role of inhibitory nature in the central nervous system.
Alanine amino acid
- It is used in the synthesis of cysteine, choline, and cephaeline.
- It takes part in the synthesis of purines and pyrimidines.
- It gives rise to glycine and pyruvic acid.
- It gives rise to glutathione, glutamine, GABA and alpha-ketoglutaric acid etc. All these have wide ranges of functions in our body.
Glutamine amino acid
- It is converted to glutamic acid.
- Its formation in the brain prevents the accumulation of ammonia, which is very toxic to nervous tissue.
Tryptophan amino acid
- It contains the indole ring and helps in the formation of niacin, a member of Vitamin B complex.
- It forms serotonin which has potent action on the brain and other parts of the body.
- It forms oxaloacetic acid.
- It acts as an excitatory transmitter.