AMINO ACID CHEMISTRY lecture 1 PDF

# Chemistry of Amino Acids and Protein ## Presenter **DR/Walaa Keshk** Professor of Medical Biochemistry Faculty of medicine, Tanta university ## Resources * Harvey, Richard A., Ph. D. (2011). Lippincott's illustrated reviews: Biochemistry. Philadelphia: Wolters Kluwer Health, * Chatterjea, M....

# Chemistry of Amino Acids and Protein ## Presenter **DR/Walaa Keshk** Professor of Medical Biochemistry Faculty of medicine, Tanta university ## Resources * Harvey, Richard A., Ph. D. (2011). Lippincott's illustrated reviews: Biochemistry. Philadelphia: Wolters Kluwer Health, * Chatterjea, M.N. and Shinde, R. (2008) Textbook of Medical Biochemistry. 7th Edition, Jaypee Brothers Medical Publishers, New Delhi. ## Intended Learning Outcomes 1. Define General Nature of Amino Acids 2. Classify Amino Acids 3. Demonstrate Properties of Amino Acids 4. Define Peptides and mention an example ## Proteins * Most important cell constituents. * Responsible for almost every function in the body. * High molecular weight organic compounds formed of linear chains of L. amino acids that are linked together by peptide bonds. * Contain **Carbon**, **Hydrogen**, **Oxygen**, **Nitrogen** (characteristic of proteins). * Each protein has specific and unique sequence of amino acids that defines both its three-dimensional structure and its biologic function. ## Amino Acid * Over 300 amino acids occur in nature * Only 20 are involved in protein synthesis (standard or primary a.a.). * They contain both acidic carboxyl group (-COOH) and a basic amino group (-NH2). * They differ from each other in their **R-groups**. * All the amino acids found in proteins are of the L-configuration. ## Amino Acid Structure A diagram of an amino acid structure with the following annotations: * **Hydrogen** * **Amino** * **Carboxyl** * **R-group (variant)** * **Acid (carboxyl group)** * **Amino (amino group)** * **Distinct Side Chain** ## Which part of the amino acid gives it uniqueness? * a) Amino group * b) Carboxyl group * c) **Side chain** * d) None of the mentioned ## Classifications of Amino Acids (a.a) * Chemical classification * Structure of the side chain of the amino acids * According to chemical nature of the amino acid * Nutritional (biological) classification * Metabolic classification (their fate in the body) * Nature or polarity of the side chain of the amino acids. ## 1) Chemical Classification of Amino Acids ### a. Aliphatic * Contain no ring * Glycine * Alanine * Serine * Threonine * Cysteine ### b. Aromatic * Contain benzene ring * Phenylalanine * Tyrosine ### c. Heterocyclic * Contain ring but other than benzene * Tryptophan * Histidine ### d. Imino acids * Proline ## Sulfer Containing a.a * Cysteine * Methionine ## Which of the following is a Sulphur containing amino acid? * a) Aspartate * b) Tyrosine * c) **Methionine** * d) Serine ## Branched chain a.a * Valine * Leucine * Isoleucine ## Hydroxy-a.a * Serine * Thereonine * Tyrosine ## 2) Their Chemical Nature of the Amino Acid in Solution ### Neutral (Monoamino and monocarboxylic) * Glycine * Alanine * Valine * Leucine * Isoleucine * Serine * Threonine * Cysteine * Methionine * Proline ### Acidic (Dicarboxylic monoamino) * Glutamic * Aspartic ### Basic (Diamino mono carboxylic) * Arginine * Histidine * Lysine ## 3) Nutritional Classification * **Non essential amino acids**: can be synthesized in the body, so they are not needed in the diet. * **Semi-essential amino acids**: Can be synthesized within the body but in insufficient for the physiological requirements of the body as in children (high rate of growth) (Arginine and Histidine) but not essential in adult. * **Conditionally essential amino acids**: the are normally non-essential, but become essential during times of physiological stress. They are Arginine, Glycine, Cysteine, Tyrosine, Proline, and Glutamine. * **Essential amino acids**: cannot be synthesized in the body, so they have to be taken in the diet, and their deficiency impairs protein synthesis results in diseases. ## Essential Amino Acids * Lysine * Isoleucine * Leucine * Valine * Tryptophan * Phenylalanine * Methionine * Threonine * Arginine * Histidine ## Non-Essential Amino Acids * Glycine * Alanine * Serine * Tyrosine * Cysteine * Asparagine * Aspartic * Glutamic acid * Glutamine * Proline ## 3. An essential amino acid in man is......... * a) Aspartate * b) Tyrosine * c) **Methionine** * d) Serine ## 3. Which of the following is an acidic amino acids * a) **Glutamate** * b) Tryptophane * c) Cysteine * d) Serine ## 4) Metabolic Classification | Classification of Amino | Amino Acid | |---|---| | Purely Ketogenic | Leucine | | Both Ketogenic and Glucogenic | Phenylalanine | | | Isoleucine | | | Tyrosine | | | Tryptophan | | | Lysine* (Predominantly Ketogenic) | | Glucogenic | Any amino acid that do not belong to the above groups | ## 5. Nature or Polarity of Side Chain of Amino Acid ### Hydrophilic (Polar) * **Negatively charged:** * Aspartic acid * Glutamic acid * **Positively charged:** * Lysine * Arginine * Histidine * **Uncharged:** * Serine * Threonine * Aspargine * Glutamine * Cysteine * Proline ### Hydrophobic (Nonpolar) * **Aliphatic Side Chain:** * Alanine * Valine * Leucine * Isoleucine * Proline * **Aromatic Side Chain:** * Tyrosine * Phenylalanine * Tryptophan ## Importance of Amino Acids * Formation of proteins and peptides. * Formation of glucose * Transport of ammonia: glutamine and alanine * Detoxification reactions: Glycine, cysteine and methionine * Formation of biologically important compounds: as neurotransmitter * Amino acids are not stored in the body. The amino acid "reserve" is the muscle mass. ## Properties of AA 1. Optically active except glycine (no asymmetric carbon atom). 2. Ionization of Amino Acids: * Acid base behavior: have carboxyl (-COOH) and amino group (-NH2) * **Buffering activity**: can act as weak acid or weak base. **histidine** serves as the best buffer at physiological pH. * Amphoteric properties (zwitter ion formation) ## Zwitter Ions or Ampholytes Molecules which carry equal number of ionizable groups of opposite charge and therefore bear no net charge are called **Zwitter ions** or **ampholytes**. Zwitter is a german word which means hermaphrodite. ## 3. The isoelectric point of an amino acid is defined as the pH.......... * a) **Where the molecule carries no electric charge** * b) Where the carboxyl group is uncharged * c) Where the amino group is uncharged * d) Of maximum electrolytic mobility ## 3. Which of the following amino acids is glucogenic and ketogenic * a) **Alanine** * b) Tyrosine * c) glycine * d) Leucine ## 2- Chemical properties 1. **Transamination**: * by transaminases requires pyrodoxal phosphate (vitamin B6). * A diagram showing the transamination reaction with the following annotations * Amino Acid - 1 * Ketoacid - 1 * PLP * Transaminase (aminotransferase) * Ketoacid - 2 * Amino Acid - 2 2. Oxidative **deamination**: amino acid is converted to the corresponding α-keto acid. * A diagram showing the oxidative deamination reaction with the fotllwing annotations: * Glutamate * αKetoglutarate * Glutamate dehydrogenase * NAD(P)* * NH3 * NAD(P)H + H* 3. **Transdeamination** * Transamination + Oxidative Deamination = Transdeamination 4. **Decarboxylation**: * $R-CHNH_2-COOH --> R-CHNH_2 + CO_2$ * A.A. gives the corresponding amine. e.g * Histidine to histamine (vasodilator and imp, in allergic reaction). * Glutamate to GABA (inhibitory neurotransmitter) * Pyridoxal phosphate is the coenzyme for this reaction. 5. **Peptide formation** * Peptides are chains (polymer) of amino acids joined by peptide bonds. * **Peptide bond formed**: between the carboxyl group of one AA and the amino group of the next with H2O molecule release (condensation reaction). * A diagram illustrating the formation of a peptide bond. * **oligopeptide** (2-10), **polypeptide** (11-49) with a free amino group (amino terminal) and the other end has a free carboxyl group (carboxylic terminal). * A diagram of an oligopeptide chain with the following annotations: * Amino-terminal residue * Carboxyl-terminal residue ## A tripeptide has * a) 3 amino acids and 1 peptide bond * b) 3 amino acids and 2 peptide bonds * c) **3 amino acids and 3 peptide bonds** * d) 3 amino acids and 4 peptide bonds ## A transaminase enzymes requires * a) **Pyrodoxal phosphate** * b) Biotin * c) Folic acid * d) Vitamin C ## Glutathione * Tripeptide formed of **Glutamate** - **cysteine** - **glycine**. * Found in 2 forms: reduced (G-SH) and oxidized (GS-SG) states. * **Importance** * Reduced form serve as antioxidant * Maintain normal red blood cells structure * Keep hemoglobin in ferrous state. * Transport of amino acids across the cell membrane of the kidney and intestine. ## The amino acid required for the formation of glutathione * a) Glycine, alanine, tyrosin * b) Cysteine, glycine, asparate * c) **Glutamate, cysteine, glycine** * d) Glutamate, glycine, alanine.