Amino Acids Classification PDF

PROTEIN CHEMISTRY AMINO ACIDS CLASSIFICATION BY/ MEDICAL BIOCHEMISTRY & MOLECULAR BIOLOGY DEPARTMENT HELWAN UNIVERSITY DR./MARWA KAMEL  Outlines Amino acids Amino acids Structure classification Amino acids...

PROTEIN CHEMISTRY AMINO ACIDS CLASSIFICATION BY/ MEDICAL BIOCHEMISTRY & MOLECULAR BIOLOGY DEPARTMENT HELWAN UNIVERSITY DR./MARWA KAMEL  Outlines Amino acids Amino acids Structure classification Amino acids Properties  OBJECTIVES Classify amino acids. Demonstrate structure of amino acids. Outline the properties of amino acids.  Amino Acids are the Building Blocks of Proteins AA AA AA AA AA AA One Protein Amino Acid AA AA AA AA AA The 20 Key Amino Acids More than 300 amino acids occur naturally, but 20 of them that make up proteins. These 20 amino acids are the building blocks of proteins. Amino acid structure Each amino acid has 4 different groups attached to α- carbon ( which is C-atom next to COOH). These 4 groups are : ▪ Amino group (NH2) ▪ Carboxyl group(COOH) ▪ Hydrogen atom R ▪ Side Chain (R) Amino acid structures differ at the side chain (R- groups). Amino acids are α- amino acids (The amino group attached to the α- carbon which is C-atom next to COOH group). L-amino acids (The amino group is on left side configuration) Some D-amino acids occur in nature, but not in proteins. α- L-Form Amino Acid Structure Carboxylic group - COO Amino group + H3N a H R Amino acids classification  Classification of Amino Acids Chemical Based on different methods According Polarity of the side chain to polarity Based on whether amino acid can Nutritional be synthesized or not in the body Based on the fate of amino acids Metabolic in the body Chemical Classification 1- According to number of carbon atoms. 2- Amino acids and Imino acid. 3- Acidic , Basic and Neutral amino acids. 4- Sulfur and Hydroxy containing amino acids. 5- Aromatic ,Heterocyclic and Aliphatic AAs. 6- Branched and Nonbranched chain AAs. 7- Amide group-containing amino acids. According to number of carbon atoms 2 Carbons containing A.A Glycine 3 Carbons containing A.A Alanine Serine Cysteine  Phenyl alanine Tyrosine Tryptophan  Histidine 4 Carbons containing A.A Methionine Threonine 5 Carbons containing A.A Arginine Valine 6 Carbons containing A.A Lysine Leucine Isoleucine Imino acid: Proline Acidic , Basic and Neutral amino acids: Acidic Amino Acids (di-carboxylic groups)  Basic Amino Acids (di-amino groups) Sulfur containing amino acids: Cysteine Methionine Hydroxy amino acids: Serine Tyrosine Threonine Aromatic amino acids (contain benzene ring) Phenyl alanine Tyrosine Tryptophan Heterocyclic amino acids(contain other type of ring) Histidine Proline Tryotophan Aliphatic amino acids (contain No ring) Other amino acids Branched chain amino acids Valine Leucine Isoleucine Amide group-containing amino acids: e.g. Glutamine and Asparagine N.B Derived Amino Acids: β-alanine in vitamin structure. γ-amino butyric acid (GABA) neurotransmitter. Hydroxy-proline, hydroxy-lysine found in proteins.(structure of collagen) Ornithine, Citrulline in urea cycle.  Cystine formation of 2 mlecules of cysteine. Classification based on Polarity of side chain Amino Acids Hydrophilic aa Hydrophobic aa Basic side chain aa Acidic side chain aa Polar, uncharged side chain aa  Classification according to polarity Hydrophilicity R-Group Polar Non-Polar Hydrophilic Hydrophobic Able to react with water Unable to react with water Can form Hydrogen bond with water Can not form hydrogen bond with water Classification according to polarity Polar Non polar Occur on the Buried in the surface of the interior of proteins cytosolic proteins Present in direct contact with Away from water water Share in hydrophobic interactions Polar (Hydrophilic) side chain They have polar groups in their side chain that can participate in hydrogen bond formation with water. They include ; uncharged side-chain (OH-SH-Amide): e.g. Serine, Threonine, Tyrosine, Cysteine, Asparagine and Glutamine.  charged side-chain a) Amino acids with a positively (+ve) charged side-chain (basic amino acids) Lysine, Arginine and Histidine. b) Amino acids with a negatively (-ve) charged side-chain (acidic amino acids) Glutamic acid and Aspartic acid. Non-polar (Hydrophobic side-chain): Other amino acids with a side chain that does not participates in hydrogen bonds formation with water.  Classification based on nutritional requirements (Biological classification) i) Essential amino acids: These amino acids cannot be synthesized in the body and have to be present essentially in the diet. e.g. Valine, Isoleucine, Leucine, Lysine, Arginine, Methionine, Threonine, Tryptophan Phenylalanine, and Histidine. ii) Semi-essential amino acids: These amino acids can be synthesized in the body but the rate of synthesis is lesser than the requirement (e.g. during growth, repair or pregnancy) e.g. Arginine and Histidine. iii) Non-essential amino acids: Other amino acids that are synthesized in the body, thus their absence in the diet does not affect the growth. e.g.- Other remaining amino acids. Essential AA Nonessential AA Isoleucine Alanine Leucine Asparagine Lysine Aspartic Acid Methionine Cysteine Phenylalanine Glutamic acid Threonine Glutamine Tryptophan Glycine Valine Proline Arginine Serine Histidine Tyrosine  Biological value of protein When a protein contains the essential amino acids, it has a high biological Value. When one or more of the essential amino acids are missing or present in low numbers, the protein is has a low biological value. Animal sources provide a complete source of protein (i.e. containing all essential amino acids), whereas vegetable sources generally lack one or more of the essential amino acids.  Classification based on metabolic fate The carbon skeleton of amino acids can be used either for glucose production , ketone bodies production Or both ▪ Pure ketogenic Leucine and Lysine ▪ Glucogenic and ketogenic (Mixed) Isoleucine, Tyrosine, Phenylalanine and Tryptophan ▪ Pure Glucogenic The remaining amino acids are glucogenic Which amino acid is not basic? a. Histidine b. lysine c. asparagine d. arginine e. Non of the above Proline amino acid: a- Is a dicarboxylic monoamino acid. b- Has a positively charged R-group c- Is considered an imino acid d- Non of the above Which of the following is not an essential amino acid? A-histidine B-lysine C-tryptophan D-alanine Phenyl alanine amino acid : a- is a heterocyclic amino acid b- has a negatively charged R-group c- is a non polar amino acid d- is a non essential amino acid An aromatic amino acid is (A)Lysine (B) Tyrosine (C) Taurine (D) Arginine  An essential amino acid in man is (A)Aspartate (B) Tyrosine (C) Methionine (D) Serine Non essential amino acids (A) Are not components of tissue proteins (B) May be synthesized in the body from essential amino acids (C) Have no role in the metabolism Which one of the following is semiessential amino acid for humans? (A)Valine (B) Arginine (C) Lysine (D) Tyrosine An example of polar amino acid is (A)Alanine (B) Leucine (C) Arginine (D) Valine A ketogenic amino acid is (A)Valine (B) Cysteine (C) Leucine (D) Threonine  Properties of Amino Acids Soluble in Amphoteric Colorless polar solvent Property Isoelectric Buffering point activity 1-Amino Acids Solubility Soluble in polar Insoluble in solvents like non polar water and alcohol solvents due to presence of charged groups  2-Amino acids are colorless But colorless Amino Aromatic acids do amino acids not absorb absorb visible light ultraviolet light (wave length 280nm)  3-Amphoteric Property The property of amino acid to COO - a behave as an acid +H (proton donor) or 3N H as a base (proton acceptor) R group  Amphoteric property Alkaline Carboxyl group donates a proton Amino acid becomes negatively charged media(low H AA migrates to the anode in an electric concentration) field. Acidic Amino group accept a proton Amino acid becomes positively charged media(high H AA migrates to the cathode in an electric concentration) field. Acidic environment Neutral environment Alkaline environment NH2 H+ NH2 H+ NH2 R-C-H R-C-H R-C-H COOH COO- COO- +1 0 -1 Isoelectric point Juang RH (2004) BCbasics 4-Isoelectric point  Zwitter ion amino acids are zwitter ions (dipolar ions) when they are electrically neutral: Amino group = -NH3+ Carboxyl group = -COO-  Higher pH Isoelectric point More basic Basic solution (Lower Hydrogen Concentration) AAs Carry Negative charge  Lower pH Isoelectric More acidic point Acidic solution (high hydrogen Concentration) AAs carry Positive chargre All the followings are true about Zwitter ion EXCEPT a- is formed at the isoelectric point b- is a dipolar ion c- is formed at a specific pH for each amino acid d- migrates to the cathode in an electric field At neutral pH, a mixture of amino acids in solution would be predominantly: (A) Dipolar ions (B) Nonpolar molecules (C) Positive and monovalent (D) Hydrophobic  Summary 1- Biological classification of amino Acids: Essential and non-Essential 2- Metabolic classification of Amino Acids glucogenic, ketogenic, mixed 3- By polarity : polar (charged- non charged) and non polar 4-Properties of Amino Acids: -Amphoteric property In a Basic solution (Lower Hydrogen Concentration) AAs Carry Negative charge. Acidic solution (high hydrogen Concentration)AAs carry Positive charge. - Isoelectric point (I.E.P) The specific pH at which the AA can exist in dipolar form with zero net charge.