Amino Acid Chemistry
•Download as PPTX, PDF•
0 likes•17 views
Understanding the chemistry and classification of Amino Acids.
Recommended
More Related Content
Similar to Amino Acid Chemistry
Similar to Amino Acid Chemistry (20)
Recently uploaded
Recently uploaded (20)
Amino Acid Chemistry
- 1. Amino Acid and Protein Chemistry KARTHIK G KAMATH K ASSISTANT PROFESSOR OF BIOCHEMISTRY
- 2. Objectives Define amino acids Describe general structure of amino acids Describe standard amino acids Classify amino acids based on their structure
- 3. Amino acids Group of organic compounds containing amino and carboxylic acid groups Carboxylic acid – acidic Amino - alkaline
- 4. General Structure of Amino Acids α-amino acids – both amino and carboxylic acid groups attached to same carbon atom α-carbon atom binds to a side chain – R R is different for each amino acids
- 5. Standard Amino Acids 300 amino acids occur in nature Only 20 are found repeatedly in protein structure – standard amino acids Due to universal nature of the genetic code available for incorporation of only 20 amino acids during protein synthesis In turn controlled by DNA
- 6. Classification of amino acids based on structure (composition) Amino acids with aliphatic side chain Monoamino monocarboxylic acids Leu, Ile and Val contain branched aliphatic side chains Referred as branched chain amino acids
- 7. Hydroxyl group containing amino acids Tyrosine – aromatic in nature Usually considered under aromatic amino acids
- 8. Acidic amino acids Dicarboxylic monoamino acids Aspargine and glutamine are amides
- 9. Aromatic amino acids Histidine can also be considered
- 10. Objectives Classification based on polarity Classification based on nutrition Classification based on their metabolic fate Describe proteins
- 11. Classification of amino acids based on polarity Polarity is important for protein structure
- 12. Classification of amino acids based on polarity
- 13. Classification of amino acids based on nutrition All standard amino acids need not be taken in diet
- 14. Classification of amino acids based on their metabolic fate
- 15. Functions of amino acids Amino acids also carry out functions other than protein formation D-penicillinamine – antibiotic N-acetylcysteine – antioxidant . Treatment of cystic fibrosis & chronic renal insufficiency Gabapentin - anticonvulsant
- 16. Amino acids Functions Ornithine, citrulline, argininosuccinic acid Intermediates in biosynthesis of urea Thyroxine, triiodothyronine Thyroid hormone – tyrosine S-adenosylmethionine Methyl donor Homocysteine Intermediate in methionine metabolism Homoserine Intermediate in threonine, aspartate & methionine metabolism
- 17. Objectives Define peptides Describe peptides Describe biologically important peptides Define proteins Classification of proteins based on function
- 18. Peptides Molecules with less than 10 amino acids Display wide variety of biological functions Glutathione Tripeptide Widely distributed in nature and exists in reduced / oxidized states
- 19. Functions of glutathione Serves as coenzyme – prostaglandin PGE2 synthase Prevents oxidation of sulfhydryl groups of proteins. Essential for protein function Along with glutathione reductase participates in correct disulfide bond formation Maintains RBC membrane structure and integrity Protects Hb from oxidative damage Involved in amino acid transport in intestine and kidney via meister cycle Involved in detoxification process Scavenges toxic amounts of peroxides and free radicals through glutathione peroxidase
- 20. Other peptides Peptides Description Biological function Thyrotropin releasing hormone Tripeptide secreted by hypothalamus Stimulates pituitary to release TSH Vasopressin Nonapeptide produced by post. pituitary Stimulates kidneys to retain water and increase BP Oxytocin Nonapeptide secreted by post. pituitary Causes contraction of uterus Angiotensins Angiotensin I – decapeptide Angiotensin II – octapeptide Stimulates release of aldosterone form adrenal glands Methionine enkephalin Pentapeptide found in brain Inhibits sense of pain Bradykinin & kallidin Nona and decapeptides Powerful vasodilators Peptide antibiotics Gramicidin, bacitracin, tyrocidine & actinomycin Aspartame Dipeptide – aspartic acid and phenylalanine 200 x sweeter than sucrose. Used as artificial sweetener GI hormones Gastrin, secretin etc.
- 21. Proteins Most abundant organic molecules in the living organism Polymers made up of amino acids
- 22. Classification of proteins 3 majors basis – function, composition & shape
- 23. Objectives Classify proteins based on shape Classify proteins based on composition Classify proteins based on nutrition
- 24. Classification of proteins based on shape Into 2 groups Globular Proteins Fibrous Proteins • Spherical/oval in shape • Soluble in water / solvents • Digestible • E.g. • Serum albumin • Serum globulin • Thymus histones • Elongated and fibre like shape • Insoluble in water • Resistant to digestion • E.g. • Collagen • Elastin • keratin
- 25. Classification based on composition Can be broadly classified into three sub groups Simple proteins – composed of only amino acid residues Conjugated proteins – along with amino acid these contain a non-protein moiety (prosthetic group) Derived proteins – denatured/degraded products of simple / conjugated proteins
- 26. Simple proteins Sl.n Sub class Description Examples 1 Albumins Soluble. Coagulated by heat Serum albumin, lactalbumin 2 Globulins Neutral/dil. solutions Serum globulin, vitelline 3 Glutelins Dil. acids/alkalies Glutelin, oryzenin 4 Prolamines 70% alcohol Gliadin, zein 5 Histones Strongly basic proteins Thymus histones 6 Globins Considered along with histones 7 Protamines Resembles histones, smaller in size Sperm proteins 8 Lectins Carb binding proteins Agglutinin 9 Collagens Connective tissue proteins 10 Elastins Found in tendons and arteries 11 Keratins Hair and nail
- 27. Conjugated proteins Along with amino acid residues also contains non-protein moiety known as prosthetic group / conjugating group Nucleoproteins – Nucleic acid is the prosthetic group. E.g. histones, nucleoprotamines Glycoproteins – prosthetic group is carbohydrates. E.g mucin, ovomucoid Lipoproteins – in combination with lipids. E.g. serum lipoproteins Phosphoproteins – phosphoric acid. E.g. casein, vitelline Chromoproteins – prosthetic group coloured in nature. E.g. Hb, cytochromes Metalloproteins – metal ions. E.g. ceruloplasmin, carbonic anhydrase
- 28. Derived proteins Denatured or degraded products of simple & conjugated proteins They are of 2 types Primary derived proteins Secondary derived proteins
- 29. Classification of proteins based on nutrition Nutritive value is determined by composition of essential amino acids
- 30. Objectives Describe transamination Explain transamination Describe deamination Explain deamination Explain fate of ammonia
- 31. Introduction Amino acids undergo transamination followed by deamination to release ammonia Amino group is utilized to produce urea. Which is the end product of protein metabolism
- 32. Transamination Transfer of amino group from amino acids to ketoacid Process involves interconversion of pair of amino acids & keto acids Reaction is catalysed by transaminases
- 33. Salient features of transamination 1. All transaminases require pyridoxal phosphate (PLP) 2. Specific transaminases exists for each pair. Only aspartate transaminase and alanine transaminase make significant contribution 3. Free ammonia is not liberated. Only transfer of amino group 4. Transamination is reversible 5. Very imp for redistribution of amino groups & production of non-essential amino acids 6. Diverts excess amino acids towards energy generation 7. Transamination concentrates ammonia into glutamate. Glutamate undergoes deamination 8. All amino acids except lysine, proline, threonine and hydroxyproline undergoes transamination 9. Not restricted to only α-amino acids 10. serum transaminases important for diagnostic purposes
- 34. Mechanism of transamination Occurs in 2 stages a) Transfer of amino group to PLP to form pyridoxamine phosphate b) The amino group then transferred to a keto acid to from a new amino acid
- 35. Deamination Removal of amino group from amino acid as ammonia Results in liberation of ammonia for urea synthesis May be oxidative or non-oxidative Transamination and deamination occur simultaneously – transdeamination
- 36. Oxidative deamination Deamination coupled with oxidation In liver and kidneys To provide ammonia for urea synthesis and α-keto acids for variety of reactions Glutamate produced during transamination serves as collection centre of amino groups Glutamate undergoes rapid oxidative deamination to liberate ammonia. Catalysed by glutamate dehydrogenase Conversion of glutamate to α-ketoglutarate occurs through an intermediate α-iminogluterate
- 37. Non-oxidative deamination Some amino acids can be deaminated to liberate ammonia without oxidation Amino acid dehydrases Serine, threonine and homoserine are OH-amino acids Undergo non-oxidative deamination catalysed by PLP-dependent dehdrases Serine Threonine homoserine Dehydratase NH3 Respective α-keto acids
- 38. Deamination of histidine Histidase acts on histidine to liberate ammonia Histidine Histidase NH3 Urocanate Amino acid desulfhydrases Cysteine & homocysteine coupled with desulfhydration to form keto acids Cysteine Desulfhydrases NH3+H2S Pyruvate
- 39. Fate of ammonia Ammonia exists as ammonium (NH4 +) ion Formation of ammonia Transport and storage of ammonia Occurs mainly b/w tissues and liver in the form of glutamine or alanine Glutamine can be deaminated by glutaminase Functions of ammonia Involved in synthesis of many products like – non-essential amino acids, purines & pyrimidines, amino sugars, aspargine etc. Very imp to maintain acid base balance
- 40. Disposal of ammonia Converted to non-toxic urea and excreted Toxicity of ammonia Harmful to the brain Slurring of speech and blurring of vision Tremors May lead to coma and finally, death
- 41. Objectives Describe urea cycle Explain the reactions of urea cycle Describe the regulation of urea cycle Describe the energetics of urea cycle Describe disorders of urea cycle
- 42. Urea cycle Urea is end product of protein metabolism Synthesized in liver Transported to kidneys for excretion in urine Also called as Krebs-Henseleit cycle Urea has 2 amino groups First two steps occur in mitochondria Rest in cytosol
- 43. Reactions of urea cycle CO2 + NH+ 4 Carbamyl phosphate Citrulline Aspartate Argininosuccinate Arginine Fumerate Ornithine Urea H2O Carbamyl phosphate synthase I Ornithine transcarbamylase Argininosuccinate synthase argininosuccinase Arginase MITOCHONDRIA CYTOSOL 2 ATP 2 ADP+Pi NAG ATP AMP+PPi
- 44. Regulation of urea cycle Carbamoyl phosphate synthase I is rate limiting step Allosterically activated by N-acetylglutamate and acetyl coA
- 45. Energetics of urea cycle Irreversible and consumes 4 ATPs 2 ATP is utilized for synthesis of carbamoyl phosphate One is converted to AMP to produce arginiosuccinate which is equal to 2 ATPs. Hence 4 ATPs are consumed
- 46. Metabolic disorders of urea cycle All disorders invariably lead to build up of blood ammonemia (hyperammonemia) Leading to toxicity Disorder Enzyme involved Hyperammonemia type I CPS I Hyperammonemia type II Ornithine transcarbamoylase Citrullinemia Argininosuccinate synthase Argininosuccinic aciduria Arginosuccinase Hyperargininemia Arginase
- 47. THANK YOU