E) Synthesis of α - amino acids

Protein can be hydrolyzed by refluxing with dilute hydrochloric acid to give a mixture of α - amino acids. The resulting mixture can be separated by  (a)    fractional crystallization.  (b)    Fractional distillation of their ester followed by hydrolysis (Fischer’s method) (c)    Selective precipitation as salt with phosphotungstic and picric acid.  (d)    Distribution of amino acid between n – butanol saturated with water (Dakin’s method).  (e)    Column, paper and gas chromatography.  (f)    Electrophoresis.

By amination of α- halo acid

ByStreckerSynthesis

(i)

 

6)Conceptaboutpeptidesandproteins, its general characteristic. Biological role of peptides and proteins.

Proteins consist of amino acids which are characterized by the -CH(NH₂)COOH substructure. Nitrogen and two hydrogens comprise the amino group, -NH₂, and the acid entity is the carboxyl group, -COOH. Amino acids link to each when the carboxyl group of one molecule reacts with the amino group of another molecule, creating a peptide bond -C(=O)NH- and releasing a molecule of water (H₂O). Amino acids are the basic building blocks of enzymes, hormones, proteins, and body tissues. A peptide is a compound consisting of 2 or more amino acids. Oligopeptides have 10 or fewer amino acids. Polypeptides andproteins are chains of 10 or more amino acids, but peptides consisting of more than 50 amino acids are classified as proteins.

In the animal kingdom, peptides and proteins regulate metabolism and provide structural support. The cells and the organs of our body are controlled bypeptide hormones (see table below). Insufficient protein in the diet may prevent the body from producing adequate levels of peptide hormones and structural proteins to sustain normal bodily functions. Individual amino acids serve as neurotransmitters and modulators of various physiological processes, while proteins catalyze most chemical reactions in the body, regulate gene expression, regulate the immune system, form the major constituents of muscle, and are the main structural elements of cells. Deficiency of good quality protein in the diet may contribute to seemingly unrelated symptoms such as sexual dysfunction, blood pressure problems, fatigue, obesity, diabetes, frequent infections, digestive problems, and bone mass loss leading to osteoporosis. Severe restriction of dietary protein causes kwashiorkor which is a form of malnutrition characterized by loss of muscle mass, growth failure, and decreased immunity.

Many structures of the body are formed from protein. Hair and nails are made of keratins which are long protein chains containing a high percentage (15%-17%) of the amino acid cysteine. Keratins are also components of animal claws, horns, feathers, scales, and hooves. Collagen is the most common protein in the body and comprises approximately 20-30% of all body proteins. It is found in tendons, ligaments, and many tissues that serve structural or mechanical functions. Collagen consists of amino acid sequences that coil into a triple helical structure to form very strong fibers. Glycine and proline account for about 50% of the amino acids in collagen. Gelatin is produced by boiling collagen for a long time until it becomes water soluble and gummy. Tooth enamel and bones consist of a protein matrix (mostly collagen) with dispersed crystals of minerals such as apatite, which is a phosphate of calcium. By weight, bone tissue is 70% mineral, 8% water and 22% protein. Muscle tissue consists of approximately 65% actin and myosin, which are the contractile proteins that enable muscle movement. Casein is a nutritive phosphorus-containing protein present in milk. It makes up approximately 80% of the protein in milk and contains all the common amino acids.