6-N methyl lysine is a component of myosin, which is the contractile protein found in muscles. 6-N methyl lysine is an amino acid which occurs naturally in biofluids of human beings.

Vitamin-D3 or Cholecalciferol is synthesized in skin. At first previtamin-D is produced non-enzymetically in skin from 7-dehydrocholesterol with the help of UV rays of sunlight. Then it undergoes several reactions for some time to form cholecalciferol.

Cholesterol is an important sterol found in animal tissues. A sterol is the one in which the steroid nucleus (4 fused rings in which 3 rings have 6 carbons and 1 has 5 carbons) contains one or many hydroxyl groups but no carboxyl or carbonyl groups. It is an important component of plasma lipoproteins and plasma membrane. Cholesterol has a polar hydroxyl group on C-3 and also a hydrocarbon side chain on C-17.

Hyaluronic acid is the straight chain polymer of N-acetylglucosamine and D-glucoronic acid,  which is linked together by (β-1 -> 3) linkages. Hyaluronic acid or hyaluronate is a glycosaminoglycan,  which is found in abundance in animal tissues and also in bacteria.

Gangliosides are glycosphingolipids which are obtained from glucosylceramide. Gangliosides can contain more than one molecule of sialic acid along with galactose, glucose and ceramide. They are present in the nervous tissues in the form of membrane lipids.

Maltose (C₁₂H₂₂O₁₁) is a reducing disaccharide which is obtained from the hydrolysis of starch with the help of amylases. Maltose in α and β forms are linked with α-1, 4-glycosidic linkage. Maltose is a crystalline solid, white in color and has melting point of about 160-165°C.

The secondary structure of protein is formed by the folding of linear polypeptide chain into regular structure. The folding of polypeptide chain occurs because NH and CO group in the peptide chain are linked with hydrogen bonds. The α-helix is a rod-like structure. There is an imaginary axis at the middle of the helix. Around the imaginary axis, the polypeptide chain is wound tightly.

Depending on the composition, simple proteins are those proteins, which consist of amino acid residues only. They do not contain any other chemical components. Chymotripsinogen is one such simple protein.

Retinoic acid, a Vitamin-A derivative is obtained from oxidation of retinal. 9-cis retinoic acid and trans-retinoic acid control development, growth and differentiation of tissues. It also controls gene expression.

Pyridoxine or Vitamin-B6 plays a major role in the metabolism of amino acids and glycogen. It acts as the coenzyme in decarboxylation and transamination of amino acids. It also plays a significant role in the action of steroid hormone.

Non-polar aliphatic amino acids have hydrophobic and non-polar R groups. Glycine is a non-polar aliphatic amino acid. Polar uncharged amino acids have hydrophilic R groups. Glutamine is a polar uncharged amino acid. Aromatic amino acids are non-polar and contain aromatic side chains. Tyrosine is an aromatic amino acid. Negatively charged amino acids possess R groups with net negative charge. Glutamate is a negatively charged amino acid. Positively charged amino acids have R groups, which are hydrophilic and with positive charge. Histidine is a positively charged amino acid.

Xerophthalmia is a disease in which the cornea and conjunctiva of the eye get dried due to prolonged Vitamin-A deficiency. In this condition the eye fails to produce tears. Vitamin-A deficiency also causes dryness in mucous membrane, skin and delayed growth and development.

Oleic acid belongs to the class of monounsaturated fatty acids also known as monoenoic acids. Oleic acid consists of one double bond. Its systematic name is cis-9-Octadecenoic acid. Oleic acid is commonly found in natural fats.

Mucin contains O-glycosidic bond between the hydroxyl side-chain of Thr or Ser and the anomeric carbon. Mucins are capable of forming gels and therefore is an important ingredient of gel-like secretions.

The proteins having one or more oligosaccharide chains bound covalently to side-chains of polypeptides are called glycoproteins. Glycoproteins like TSH, HCG, FSH, etc., act as hormones. Other glycoproteins include transferrin, immunoglobin, lectin, calnexin, etc.

Cellulose on hydrolysis produces cellobiose and β-D-glucose. The first step involves breaking of β-glycosidic bonds with the help of β-1, 4 glucanase to form cellobiose. Then, the β-1, 4 glycosidic bond is cleaved with the help of β-glucosidase to form glucose.

Vitamin B2 acts as the coenzyme in reactions where oxidation and reduction take place. Its deficiency causes abrasion at corners of lips, tongue and mouth. Vitamin A occurs in the retina of vertebrates in the form of visual pigments. Its deficiency causes night blindness. Vitamin C is an antioxidant and its deficiency causes low and scurvy healing of wounds. Vitamin D maintains balance of calcium and its deficiency causes rickets due to improper mineralization of bones. Vitamin B12 acts as the coenzyme in metabolism of folic acid and its deficiency causes pernicious anaemia.

Starch is found in amyloplasts and chloroplast of plant cells in higher plants in the form of compact and insoluble granules. Dextrans occur in yeast and bacteria in the form of a stock polysaccharide. Glycogen is found in abundance in the liver of animals and forms the most essential food reserve in animals. It is also called animal starch. Chitin is found in abundance in insects and arthropods like crabs. Vertebrates cannot digest chitin. Inulin occurs in roots and tubers of onions, garlic, dahlias and dandelion. It is white powdery in nature and can be used to determine the functioning of kidney by measuring Glomerular Filtration Rate.

Cellulose (a fibrous structural polysaccharide) is an unbranched and linear polymer of β-D-glucose attached with a (β-1 -> 4) glycosidic linkage. It is also known as anhydride of β-D-glucose.

Linoleic acid, arachidonic acid and linolenic acid are together known as Essential Fatty Acids (EFA). These fatty acids are not synthesized in the body and ingested by humans and animals for proper working of the cells. Two fatty acids: Linoleic acid (belonging to ω-6 fatty acid) and α-Linolenic acid (belonging to ω-3 fatty acid) are necessary in humans.