Amino Acids: Structure, Classification, and Function, Essays (high school) of Biology

Download Amino Acids: Structure, Classification, and Function and more Essays (high school) Biology in PDF only on Docsity! Structure of Amino Acids DR. K IRAN MEENA 05/9/2019 8:00-9:00 AM Specific Learning Objectives 1. General Structure of amino acids 2. Amino acids classification based on: •Standard and Non-standard amino acids (aa) •Essential and non-essential aa •Ketogenic and Glucogenic aa •Side chain functional group 3. Function of essential amino acids Genetic information is transcribed from a DNA sequence into mRNA and then translated to amino acid sequence of a protein Fig. 2.1. Textbook of Biochemistry with Clinical Correlations, 4th edition by Thomas M Devlin General Structure of Common Amino Acids •General structure of amino acids , group and a variable side chain •Side chain determines: protein folding, binding to specific ligand and interaction with its environment •Amino acids consists of a constant COOH (R is side chain) •At neutral pH, H2N- protonated to H3N+-, and –COOH deprotonated to –COO- Fig.4.2. Biochemistry. 4th edition by Donald Voet and Judith G. Voet Amino-Acids Classification Based on Standard and Non- Standard Amino Acids 1. Standard amino-acids: Those 20 amino acids are encoded by universal genetic code 2. Non-Standard amino-acids: Two amino acids incorporated into proteins by unique synthetic mechanism •Selenocysteine: Incorporated when mRNA translated included SECIS (selenocysteine insertion seq) element, causes the UGA codon to encode selenocysteine instead of stop codon) •Pyrrolysine: used by methanogenic archaea in enzyme that they use to produce methane. It is coded for UAG stop codon. Non-Standard Amino Acids •Selenocysteine, 21st protein L-α amino acids •Selenium atom replaces the sulfur of its elemental analog, cysteine •Selenocysteine is not the product of a posttranslational modification, but is inserted directly into a growing polypeptide during translation. • Selenocysteine is charged on a special tRNA called tRNASec specific for UGA (STOP)codon inserted into growing polypeptide during translation Other Classification of Amino Acids •Non-protein aa: Not naturally encoded by genetic code but found in free state as intermediates of metabolic pathway for standard aa: Ornithine and citrulline are intermediates in urea biosynthesis. • Non α-aa: -NH2 group not attached to α-carbon atom but some other carbon atom. Ex. γ-aminobutyric acid (GABA) and β-alanine. •Modified protein aa: Amino acids modified after they incorporated into protein. Proline and lysine undergo hydroxylation to become hydroxyproline and Hydroxylysine. Essential for formation of mature collagen. AA Classified on Basis of Nutritional Requirement •Essential amino acids: Not synthesised in the body and must be supplied in diet •Non-essential amino acids: Synthesized in body and there is no diet dependency for them •Semi-essential amino acids: Not synthesised in the body in adequate amounts and requires dietary supplementation. Amino-Acids Classification Based on Side Chain Groups •Based on type of functional group (R group) present amino acids are classified as: Aliphatic, aromatic, acidic, basic, acid amide, sulfur and cyclic amino acids. •Based on characteristic of functional group amino acids are classified as: polar and non-polar amino acids. •Based on site of attachment of functional group. They are also classified as: alpha, beta, gamma and delta amino acids. www.khanacademy.org Amino Acids Classification based on hydrophobic and hydrophilic property Table 3.1. Harper’s Illustrated Biochemistry 30 edition Isopropyl R group Branching in isobutyl side chain on γ carbon of amino acid Branching in isobutyl side chain on β carbon of amino acid Nonpolar/Hydrophobic Methyl R group Cont-- γ β Cont-- Guanidinium R group Imidazolium R group Positively charged R groups ε-NH+ 3 R group Mentioned in amino acids with basic groups section Imino group belongs to a five-member ring Phenol R group Cont-- Benzene ring R group Heterocyclic structure, indole R group Function of Essential Amino acids Non-polar amino acids: 1. Aromatic aa: a) Phenylalanine: precursor for tyrosine, dopamine, nor-epinephrine, epinephrine and melanin. •Genetic disorder phenylketonuria is the inability to metabolize phenylalanine because of a lack of phenylalanine hydroxylase. a) Tryptophan: precursor for neurotransmitter (serotonin), hormone (melatonin) and vitamin niacin. Trp and Tyr residues anchoring membrane proteins within cell membrane. •Fructose malabsorption causes improper absorption of Trp in intestine causes reduced level of Trp in blood. c) Isoleucine: diverse physiological functions, such as assisting wound healing, detoxification of nitrogenous wastes, stimulating immune function, and promoting secretion of several hormones. 3. Sulfur-containing aa: a) Methionine: Substrate for other amino acids such as cysteine and taurine, versatile compounds such as S-adenosyl methionine and antioxidant glutathione. •Homocysteine can be used to regenerate methionine or to form cysteine. •Improper conversion of methionine can lead to atherosclerosis due to accumulation of homocysteine. Polar uncharged aa: 1. Threonine: Its residue ssusceptible to numerous posttranslational modifications. •The hydroxyl side-chain undergo O-linked glycosylation. •Threonine residues undergo phosphorylation through the action of a threonine kinase. In its phosphorylated form, it can be referred to as phosphothreonine. Its role in cell signal transduction and neural activity. Polar Charged amino-acids: 1. Positive charge/Basic aa: a) Histidine: precursor for histamine, an amine produced in the body necessary for inflammation. •Histidine ammonia-lyase converts histidine into ammonia and urocanic acid. deficiency in this enzyme in rare metabolic disorder histidinemia. Interaction with students Distributed subtopics of today’s lecture to students for participate in group discussion in next lecture. Reference Books 1) Harper’s Illustrated Biochemistry-30th edition 2) Textbook of Biochemistry with Clinical Correlations. 4th edition. Thomas M. Devlin. 3) Biochemistry. 4th edition. Donald Voet and Judith G. Voet. 4) Biochemistry 7th edition by Jeremy M. Berg, John L. Tymoczko and Lubert Stryer 5) Lehninger Principles of Biochemistry 6) Netter's essential biochemistry 1st Ed 7) https://en.wikipedia.org/wiki/aminoacids 31 THANK YOU