Lecture 4 Chapter 2 Amino Acids PDF

Lecture 4 chapter 2 Dr Ghada Mohamed 1  Amino Acids q Structure: There are about 300 amino acids occurring in nature. Only 20 of them occur in proteins. Dr Ghada Mohamed 2  Amino Acid...

Lecture 4 chapter 2 Dr Ghada Mohamed 1  Amino Acids q Structure: There are about 300 amino acids occurring in nature. Only 20 of them occur in proteins. Dr Ghada Mohamed 2  Amino Acids q Structure: Each amino acid has the following 4 groups or atoms attached to alpha (α) carbon: 1-Amino group: (NH2). 2-Carboxyl group: (COOH). 3-Hydrogen atom (H). 4- Side chain or radical group (R). Dr Ghada Mohamed 3 Dr Ghada Mohamed 4 ØCharacters of amino acids: All are α-Amino acids: i.e. the amino group attached to the second carbon (next to the carboxyl group). L-Amino acid i.e. α-amino group is on the left side configuration. Dr Ghada Mohamed 5 Dr Ghada Mohamed 6  Chemical classification: 1- According to if the amino acid is acidic, basic or neutral amino acids: Acidic amino acids: contain more than one -COOH group. EX: Aspartate and glutamate. Dr Ghada Mohamed 7  Basic amino acids: contain more than one -NH2 group. EX: ornithine, lysine, Arginine and histidine. Neutral amino acids: contain one COOH and one -NH2 groups. EX: glycine, alanine, etc. Dr Ghada Mohamed 8 Dr Ghada Mohamed 9 2-According to if the amino acid is branched or non branched: Branched amino acids: valine, Leucine and lsoleucine. Non-branched amino acids: Rest of amino acids. Dr Ghada Mohamed 10 Dr Ghada Mohamed 11 3-according to if amino acid is: aromatic, heterocyclic or aliphatic. Aromatic amino acids: which contain phenyl or phenol ring EX: Phenylalanine (phenyl ring) , Tyrosine (phenol ring). Dr Ghada Mohamed 12  Heterocyclic amino acids: which contain other type of rings: EX: Tryptophan ,Histidine,Proline and Hydroxyproline). Dr Ghada Mohamed 13  Aliphatic amino acids: include other amino acids which contain no ring. Dr Ghada Mohamed 14 4-Nutritional classification of amino acids: Based upon whether the amino acids synthesized in body or not 1 - Essential amino acids 2 - Semi - Essential amino acids 3 - Non - Essential amino acids Dr Ghada Mohamed 15 1 - Essential amino acids: Those are not synthesized in the body and must be supplied in diet. Their deficiency will affect the normal growth and health Ex: 1 - Therionine 2 - Valine 3 - Leucine 4 - Isoleucine 5 - Lysine 6 - Methionine 7 - Phenylalanine 8 - Typtophan Dr Ghada Mohamed 16 Dr Ghada Mohamed 17 2 - Semi - Essential amino acids: Not essential for adult but essential of child Synthesized in the body in amount enough for adult, but not enough for children Ex: Histidine, Arginine. Dr Ghada Mohamed 18 3 - Non - Essential amino acids: Can be synthesized in the body and so are not essential to be present in diet. Ex: the rest of amino acids Dr Ghada Mohamed 19 Dr Ghada Mohamed 20 5- Metabolic classification: Based upon the fate (metabolism) of the amino acids inside the body Carbon skeleton is converted either to glucose or ketone bodies so amino acids are classified metabolically into: 1- Ketogenic amino acid 2- Mixed amino acids (Ketogenic and Glucogenic) 3- Glucogenic amino acids Dr Ghada Mohamed 21 1- Ketogenic amino acid: This amino acid can be metabolised to ketone bodies (Leucine and lysine). 2- Mixed amino acids (Ketogenic and Glucogenic): Those amino acids can be metabolised to both glucose and ketone bodies (Threonine, isoleucine, phenylalanine, tyrosine, and tryptophan). Dr Ghada Mohamed 22 3- Glucogenic amino acids: Those amino acids can be metabolised to glucose (The rest of amino acids) Dr Ghada Mohamed 23 Ø Functions (Biomedical Importance) of amino acids: 1- Structural function: Amino acids enter in the structure of : Body peptides and proteins: as plasma proteins, tissue proteins, enzymes Hormones: as thyroxine and catecholamines. Amines: as histamine that is vasodilator. 2- Neurotansmitters: as glycine and glutamate. 3- Detoxication: as glycine. 4- Health and growth: in infants and adults. Dr Ghada Mohamed 24 o Physical properties: 1. Solubility: Amino acids may be soluble in water, dilute acids 2.Optical activity: All amino acids – except glycine are optically active because they contain asymmetric carbon atom. Dr Ghada Mohamed 25 3. Amphoteric properties and isoelectricpoint of amino acids Ø Amphoteric properties: i.e have both basic (-NH2) and acidic (-COOH) groups. Mono amino-mono carboxylic acids present in aqueous solutions as zwitter ion: Dr Ghada Mohamed 26 Ø Isoelectric pH (isoelectric point( Pi): It is the pH at which the zwitter ion is formed. Each amino acid has certain pH at Which zwitter ion is formed. The amino acid carries both positive and negative charges. It is electrically neutral and cannot migrate in electric field. Dr Ghada Mohamed 27 Dr Ghada Mohamed 28