Biomolecules

• A living system grows, sustains and reproduces itself.
• Nucleic acids are important molecules that perform two important functions.
• A nucleoside is different from a nucleotide in a specific way.
• The two strands in DNA are not identical but are complementary.
• DNA and RNA have important structural and functional differences.
• There are different types of RNA found in the cell.
• The most amazing thing about a living system is that it is composed of non-living atoms and molecules.
• The pursuit of knowledge of what goes on chemically within a living system falls in the domain of biochemistry.
• Living systems are made up of various complex biomolecules like carbohydrates, proteins, nucleic acids, lipids, etc.
• Proteins and carbohydrates are essential constituents of our food.
• These biomolecules interact with each other and constitute the molecular logic of life processes.
• Some simple molecules like vitamins and mineral salts also play an important role in the functions of organisms.
• Structures and functions of some of these biomolecules are discussed in this Unit.
• Biomolecules like carbohydrates, proteins and nucleic acids are essential for the growth, sustainability and reproduction of living systems.
• A living system grows, sustains and reproduces itself by the harmonious and synchronous progress of chemical reactions.
• Carbohydrates are primarily produced by plants and form a very large group of naturally occurring organic compounds.
• Some common examples of carbohydrates are cane sugar, glucose, starch, etc.
• Polysaccharides are carbohydrates which yield a large number of monosaccharide units on hydrolysis.
• Examples of polysaccharides include starch, cellulose, glycogen, gums, etc.
• Polysaccharides are not sweet in taste, hence they are also called non-sugars.
• Carbohydrates can also be classified as either reducing or non-reducing sugars.
• All carbohydrates which reduce Fehling’s solution and Tollens’ reagent are referred to as reducing sugars.
• All monosaccharides whether aldose or ketose are reducing sugars.
• Monosaccharides are further classified on the basis of number of carbon atoms and the functional group present in them.
• If a monosaccharide contains an aldehyde group, it is known as an aldose and if it contains a keto group, it is known as a ketose.
• The number of carbon atoms constituting the monosaccharide is also introduced in the name as is evident from the examples given in Table 10.1.
• Glucose occurs freely in nature as well as in the combined form.
• Glucose is present in sweet fruits and honey.
• Ripe grapes also contain glucose in large amounts.
• Glucose is prepared as follows: from sucrose (Cane sugar) and from starch.
• Glucose is an aldohexose and is also known as dextrose.
• Glucose is the monomer of many of the larger carbohydrates, namely starch, cellulose.
• Glucose is probably the most abundant organic compound on earth.
• Glucose was assigned the structure given below on the basis of the following evidences: its molecular formula was found to be C 6 H 12 O 6, on prolonged heating with HI, it forms n-hexane, suggesting that all the six carbon atoms are linked in a straight chain, and it reacts with hydroxylamine to form an oxime and adds a molecule of hydrogen cyanide to give cyanohydrin.
• Glucose gets oxidised to six carbon carboxylic acid (gluconic acid) on reaction with a mild oxidising agent like bromine water, indicating that the carbonyl group is present as an aldehydic group.
• Acetylation of glucose with acetic anhydride gives glucose pentaacetate which confirms the presence of five –OH groups, and on oxidation with nitric acid, both glucose and gluconic acid yield a dicarboxylic acid, saccharic acid, indicating the presence of a primary alcoholic (–OH) group in glucose.
• The exact spatial arrangement of different –OH groups was given by Fischer after studying many other properties, and its configuration is correctly represented as I.
• Gluconic acid is represented as II and saccharic acid as III.
• The distinction between a polypeptide and a protein is not very sharp.
• Polypeptides with fewer amino acids are likely to be called proteins if they ordinarily have a well defined conformation of a protein such as insulin which contains 51 amino acids.