Amino acids are organic compounds that combine together to form proteins. They contain amino (NH2) and carboxyl (COOH) functional groups, along with a side chain (R group) specific to each amino acid. The general structure is H2NCHRCOOH. Based on their R groups, amino acids are generally classified into nonpolar (hydrophobic), polar (hydrophilic), and charged amino acids. Nonpolar ones include glycine, alanine, valine etc. Polar ones include serine, threonine etc. Positively charged (basic) ones include lysine, arginine etc. Negatively charged (acidic) ones include aspartic acid, glutamic acid etc.
Essential and Non-Essential Amino Acids
Of the hundreds of different amino acids, only 20 are used by our body to synthesize proteins. These are further classified as essential and non-essential amino acids. Essential amino acids cannot be synthesized by the human body and must be obtained from dietary sources. They include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Non-essential amino acids can be synthesized in sufficient quantities in the human body. They include alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine, tyrosine and arginine.
Biosynthesis and Catabolism of Amino Acids
Living organisms have evolved complex biosynthesis and catabolic pathways to synthesize and break down amino acids. Amino acids are biosynthesized from intermediates of major metabolic pathways like glycolysis, Krebs cycle and pentose phosphate pathway. For example, certain amino acids are derived from glycolytic intermediate phosphoenolpyruvate or pyruvate. The amino group is obtained from ammonia through glutamine synthase or glutamic acid. The carbon skeletons are provided by intermediates of the citric acid cycle or other biosynthetic precursors. Biosynthesis requires aminoacyl tRNA synthetases, amino acid kinases and amino transferases as enzymes. Catabolism involves transamination and deamination to ammonia and Krebs cycle intermediates by amino acid transaminases and deaminases respectively.
Protein Synthesis and Role of Amino Acids
Proteins, made of amino acid polymers joined by peptide bonds, are required for the structure, function and regulation of the body. Amino acids are first activated by attachment to transfer RNA (tRNA) molecules with the help of aminoacyl tRNA synthetases. This ensures their delivery to the ribosomes, the sites of protein synthesis. Here, mRNA provides the code for the amino acid sequence. Aminoacyl-tRNAs, matching the mRNA codons, are added one by one by peptide bond formation catalyzed by peptidyl transferase. The newly forming polypeptide grows at its free amino end. Protein synthesis continues till a stop codon is reached. The proteins then fold into their characteristic 3D structures to perform diverse biological functions.
Amino Acids as Precursors and Enzymes
In addition to protein synthesis, amino acids also function as precursors for other important biomolecules. Glutamate, glutamine and proline act as precursors for glutathione, a major cellular antioxidant. Arginine, ornithine and citrulline are precursors for nitric oxide synthesis. Cysteine and methionine are precursors for coenzyme A and taurine, both involved in metabolic regulation. Tyrosine is the precursor for neurotransmitters dopamine, epinephrine and norepinephrine. Tryptophan is the precursor for serotonin and melatonin. Many amino acids also function directly as enzymes or enzyme cofactors. For example, cysteine acts as a catalytic or regulatory site in enzymatic reactions. Lysine acts as enzyme cofactor.
Health Effects of Amino Acids
A balanced supply of amino acids is essential for growth, maintenance and repair of tissues. Deficiency of essential amino acids leads to muscle wasting and weakness. Chronic deficiency can lead to loss of appetite, weight loss and increased risk of infection. Some specific health effects are related to certain amino acids. Supplementation with branched chain amino acids like leucine, isoleucine and valine helps delay fatigue and promotes muscle growth. Lysine supplementation improves calcium absorption and bone health. Arginine improves circulation and cardiovascular health. Glutamine reduces stress and enhances the immune system.
amino acids are organic building blocks that form the basis of protein synthesis and cellular biochemistry. They are essential for growth and maintenance of tissues. A delicate balance of amino acid availability and metabolism enables living cells to thrive. Understanding amino acid biosynthesis, transport and functions helps appreciate the molecular foundation of life.
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About Author:
Alice Mutum is a seasoned senior content editor at Coherent Market Insights, leveraging extensive expertise gained from her previous role as a content writer. With seven years in content development, Alice masterfully employs SEO best practices and cutting-edge digital marketing strategies to craft high-ranking, impactful content. As an editor, she meticulously ensures flawless grammar and punctuation, precise data accuracy, and perfect alignment with audience needs in every research report. Alice's dedication to excellence and her strategic approach to content make her an invaluable asset in the world of market insights.
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