Amino Acids and Protein Chemistry PDF

Amino Acid and Proteins Chemistry Mustapha Umar Imam, MBBS, PhD Medical Biochemistry UDUS Outline Amino Acids Classification Properties Functions Proteins: complete and incomplete  Amino Acid Amino acids are organic compounds containing amine [- NH2] carboxyl [-COOH...

Amino Acid and Proteins Chemistry Mustapha Umar Imam, MBBS, PhD Medical Biochemistry UDUS Outline Amino Acids Classification Properties Functions Proteins: complete and incomplete  Amino Acid Amino acids are organic compounds containing amine [- NH2] carboxyl [-COOH] side chain [R group] The major key elements of amino acids are carbon, hydrogen, nitrogen, oxygen. About 500 amino acids are known only 20 are relevant for humans Amino Acid o The amino group is on the  -carbon atom, the one adjacent to the carboxyl group. o With the exception of glycine, where R = H, -amino acids have a chiral carbon and are stereoisomers o cannot be superimposed: enantiomers Amino Acid D-amino acidL-amino acid Classification Based on R group: simple, branched, acidic, basic etc Polarity: non-polar, polar uncharged, - ve, +ve etc Nutritional requirements: essential and non-essential Amino Acids Amino Acids Amino Acid Amino Acid  Amino acids are joined together by peptide bonds, two amino acids produce a dipeptide (three a tripeptide) configuration of up to as many as 11-100 amino acids is known as a polypeptide more than 100 amino acids produces proteins The condensation of two amino acids to form a peptide bond: Condensation and Hydrolytic Reactions pH dependent properties Zwitterions have both positive and negative charges Amino acids can have both N-H+ and COO-. Isoelectric point: pH at which amino acids exist as zwitterions differs for each amino acid Functions of Proteins Functions of Proteins Growth and maintenance of tissues Enzymes eg hexokinase Hormones eg insulin Regulation of fluid balance Acid-base regulation Transport proteins Immunity (antibodies) Source of energy Functions of Proteins neurotransmitters eg norepinephrine and epinephrine melanin fibrin precursor to the vitamin niacin. Complete Vs Incomplete proteins Protein The quality of a protein is determined by its ability to provide the 9 essential amino acids. Proteins from animal sources (eggs, dairy, meat, poultry, and fish) and one vegetable protein (soy) are all considered high-quality because they contain all of the essential amino acids in the necessary proportions.  Complete protein contain an adequate proportion of all the essential amino acids in a diet. Proteins from animal sources (meat, poultry, milk, and fish)  Incomplete protein lack one or more essential amino acids or contain them in inadequate proportions necessary for human metabolism. Proteins from plant sources (wheat, corn, rice, and beans) have a lower quality (except soy protein)  Complementary proteins Incomplete proteins from different plant sources may be combined in such a way that the result is equivalent in nutritional value to animal protein. Ile, Leu Lys Met Trp Legumes x x Cereals x x  Proteins When there are three or more amino acids, the protein starts to form three dimensional shapes. Primary Secondary: alpha helix and beta sheets Tertiary Quarternary Proteins Polypeptide Protein shape and function Denaturing Alteration of the protein’s shape and thus functions through the use of Heat Acids Bases Salts Mechanical agitation Primary structure is unchanged by denaturing Denaturing a Protein Take home message AA are the building blocks of proteins Amino acids contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur Amino acids have a central carbon with a carboxyl group, a hydrogen, a nitrogen-containing amine group, and a unique side chain 9 essential amino acids 11 nonessential amino acids Amino acids link together with peptide bonds by condensation and break apart by hydrolysis Animal proteins are more complete Take home message Attractions and interactions between the side chains cause the proteins to fold into precise three-dimensional shapes Protein shape determines its function Proteins are denatured and their shapes changed by Heat Acids Bases Salts Mechanical agitation Questions?