Amino Acids PDF

Amino Acids Amino Acids There are about 300 amino acids occur in nature. Only 20(22) of them occur in proteins Importance They are the building blocks of proteins. :. Structure Each amino acid has 4 different groups attached to α- carbon ( which is C-atom next to COOH). These 4 gro...

Amino Acids Amino Acids There are about 300 amino acids occur in nature. Only 20(22) of them occur in proteins Importance They are the building blocks of proteins. :. 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). COOH group ( -COOH Hydrogen atom (-H Side Chain ("R-group") : : ) ) General formula of amino acid Physical properties: Solubility: All amino acids are soluble in water, dilute acids, dilute alkalis and ethanol. Malting point: Amino acids have high matting point > 200Cº that means they are very stable molecules  Amphoteric properties of amino acids Amino acids are amphoteric. They are capable of behaving as both an acid and a base, since they have both a proton donor group and a proton acceptor group. In neutral aqueous solutions the proton typically migrates from the carboxyl group to the amino group, leaving an ion with both a (+) and a (-) charge, forming “ Zwitter ion” i.e. contain both positive and negative charge. :  Zwitter ion is electrically neutral (net charge is zero) and can’t migrate into electric field.  Isoelectric point (IEP) Is the pH at which the zwitter ion is formed. e.g IEP of alanine is 6 : Classification of Amino Acids: Amino acids can be classified by several ways for example: classify according to: Nature of side chain ("R-group" Polarity of side chain ("R-group" Nutritional classification Metabolic classification.. ) ) 1/ Aliphatic Amino Acids: This include Glycine(gly Alanine (ala, A) : )  Valine (Val) Leucine (Leu Isoleucine (Ile) ) 2) Hydroxyl amino acids: The R group of these amino acids containing hydroxyl group -OH and this includes Serine (Ser) Threonine (Thr) Tyrosine (Tyr) : 3) Sulfur amino acids The R group of these amino acids containing sulfur and this includes: Methionine (Met) Cysteine (Cys, C) Cystine is 2 molecules Cysteine linked by disulfide bond  4) Acidic amino Acids: The R group of these amino acids containing acidic group (COOH) and this includes Glutamic Acid(Glu Aspartic Acids(Asp) ) :  5) Basic amino acids: The R group of these amino acids containing basic group (NH2) and this includes Histidine (His) Lysine (Lys) Arginine (Arg) :  6) Aromatic amino acids: The R group of these acid containing aromatic rings and this include: Phenylalanine (Phe) Tyrosine (Tyr) Tryptophan (Trp,)   7) Imino Acids: This include proline (Pro The side chain of proline and its α-amino group form a ring structure proline. ) Classification according to Polarity : According to polarity of side chain("R group") amino acids classify in to A) Polar amino acid B) Non polar amino acids: s : , A- Polar amino acids: The R group of this class contains polar hydrophilic group so can forms hydrogen bond with H2O In those amino acids, R may contain: 1- OH group : as in serine, threonine and tyrosine 2- SH group : as in cysteine 3- Amide group: as in glutamine and aspargine 4- NH2 group or nitrogen (basic amino acids ): as lysine, arginine and histidine 5- COOH group ( acidic amino acids): as aspartic and glutamic. B- Non polar amino acids: The R group of this class is alkyl hydrophobic group which can’t enter in hydrogen bond formation 9 amino acids are non polar glycine, alanine, valine, leucine, isoleucine, phenyl alanine, tryptophan, proline and methionine.. Nutritional classification 1) Essential Amino Acids: These amino acids can’t be formed in the body and so, it is essential to be taken in diet. Their deficiency affects growth, health and protein synthesis. Those amino acids are: Isoleucine ,Leucine ,Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine : 2) Semi essential amino acids: These are formed in the body but not in sufficient amount for body requirements especially in children. This include: Arginine Histidine 3) Non essential amino acids: These are the rest of amino acids that are formed in the body in amount enough for adults and children. They are the remaining 10 amino acids.  Non-Essential amino acids Essential amino acids 1) Alanine (from pyruvic acid) 1) Arginine 2) Asparagine (from aspartic acid) 2) Histidine 3) Aspartic Acid (from oxaloacetic acid) 3) Isoleucine 4) Cysteine 4) Leucine 5) Glutamic Acid (from oxoglutaric acid) 5) Lysine 6) Glutamine (from glutamic acid) 6) Methionine 7) Phenylalanine 7) Glycine (from serine and threonine) 8) Threonine 8) Proline (from glutamic acid) 9) Tryptophan 9) Serine (from glucose) 10) Valine 10) Tyrosine (from phenylalanine) Metabolic classification: According to metabolic or degradation products of amino acids they may be: 1- Ketogenic amino acids: which give ketone bodies. Lysine and Leucine are the only pure ketogenic amino acids. 2- Mixed ketogenic and glucogenic amino acids: which give both ketonbodies and glucose. These are: isoleucine, phenyl alanine, tyrosine and tryptophan. 3- Glucogenic amino acids: Which give glucose. They include the rest of amino acids. These amino acids by catabolism yields products that enter in glycogen and glucose formation.