Definition and Discovery of Amino Acids
Amino acids are organic compounds that combine to form proteins. They were first identified in the early 1800s and were named for their presence in protein hydrolysates, or products of protein breakdown. It was discovered that proteins could be broken down into their constituent amino acid building blocks through processes like acid hydrolysis or enzymatic breakdown. There are currently over 500 known amino acids, but only 20 are used by the human body to build proteins.
Essential vs Non-Essential Amino Acids
Amino Acid are categorized as either essential or non-essential. Essential amino acids cannot be synthesized by the human body and must be obtained through dietary intake. The nine essential amino acids for humans are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. Non-essential amino acids can be synthesized in sufficient amounts by the human body. Examples include alanine, asparagine, aspartate, cysteine, glutamine, glutamate, glycine, proline, serine, tyrosine, and arginine. While non-essential, some amino acids like cysteine and tyrosine are considered conditionally essential under certain physiological states.
Protein Synthesis and the Role of Amino Acids
Protein synthesis, also known as protein biosynthesis, is the process whereby living cells build proteins. It is a vital process that occurs in all living organisms and is regulated by the central dogma of molecular biology. Protein synthesis involves transcription of DNA to messenger RNA (mRNA), which leads to translation of mRNA into a polypeptide chain. During translation, amino acids are covalently linked through peptide bonds in the order specified by the three-base genetic codon on the mRNA. Transfer RNA (tRNA) molecules carry specific amino acids and match them to their complementary mRNA codon during chain assembly on the ribosome. This ensures that the correct amino acid sequence is produced to make a functional protein molecule. Proteins have fundamental structural and functional roles in living organisms and their synthesis from amino acids is a precisely controlled and regulated process.
Amino Acid Structure and Properties
All 20 proteinogenic amino acids share a basic structure consisting of an alpha carbon bonded to an amino group, a carboxylic acid group, a hydrogen atom and a variable side chain known as the R group. The R group gives each amino acid its unique chemical properties. Amino acids are amphoteric, meaning they can act as both acids or bases depending on pH. At biological pH, the amino group is protonated (NH3+) while the carboxyl group is deprotonated (COO-), giving amino acids a net positive charge. This allows amino acids to interact with other cellular molecules through electrostatic forces. Their side chains also allow for various interactions like hydrogen bonding, hydrophobic effects and metal chelation. Understanding amino acid structure-function relationships is key to explaining their roles in protein folding and function.
Metabolism and Transport of Amino Acids
Once digested and absorbed, amino acids circulate in the bloodstream bound to albumin proteins. They are transported into tissues and cells where protein synthesis and breakdown occur. Inside cells, amino acids participate in an array of metabolic pathways beyond protein synthesis like biosynthesis, methylation reactions and amino acid catabolism. For example, alanine and glutamine act as nitrogen shuttles during nutrient metabolism. Excess amino acids or their carbon skeletons can be converted to specialty molecules, neurotransmitters or enter energy producing pathways. Carefully regulated amino acid transport mechanisms move them into cellular compartments and organelles like mitochondria where metabolism occurs. Imbalances in amino acid availability can impair numerous metabolic functions and physiological processes.
The Importance of Amino Acids in Human Health and Disease
As the building blocks of proteins, amino acids play indispensable roles in maintaining structure and function throughout the human body. Diets lacking in essential amino acids cannot support new protein synthesis and tissue growth. Certain conditions like kidney disease require carefully controlled protein and amino acid intake. Genetic disorders of amino acid metabolism are also known, impacting neurological and physical development if left untreated. Severe deficiencies can even cause death. Some amino acids like tryptophan, glutamine and arginine also serve as precursors to important biomolecules like serotonin, glutathione and nitric oxide with wide-ranging impacts on health, cognition and disease risk. Amino acid derivatives are applied clinically as nutritional supplements for various purposes. Overall, amino acids underpin the very make-up of the human body and closely influence general well-being on a molecular level. Dysregulation of their metabolism contributes to many pathological states.
In the amino acids represent the basic building blocks of the proteins required for life. Through their peptide bonds and variable side chains, they enable the intricate structures responsible for the vast array of cellular processes in living organisms. As metabolic intermediates and precursors, amino acids also modulate countless other biochemical reactions crucial for overall health and development. Understanding their roles provides valuable insight into nutrition, genetics and disease pathogenesis at the molecular level.
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