Ch 14Biomolecules — Class 12 Chemistry, concept-first.

Every living thing is built from biomolecules -- carbohydrates, proteins, lipids and nucleic acids -- assembled from just five major elements: carbon, hydrogen, oxygen, nitrogen and phosphorus.

Carbohydrates are the most abundant organic compounds found in every living organism. They are also called saccharides, a name that comes from the Greek word 'sakcharon' meaning sugar, because a large…

A carbohydrate molecule is almost always optically active because it possesses one or more chiral (asymmetric) carbon atoms -- carbons attached to four different groups.

Carbohydrates are classified into three major groups based on their product of hydrolysis. Monosaccharides are the simple sugars that cannot be hydrolysed into any smaller carbohydrate unit; oligosacc…

Glucose is a simple sugar that serves as the major energy source for the human body. It is the most important and most abundant monosaccharide, occurring free in honey and in sweet fruits such as grap…

Fructose is another commonly encountered monosaccharide, sharing the same molecular formula as glucose (C₆H₁₂O₆) but differing in its properties: it is levorotatory and is a ketohexose rather than an…

Disaccharides are sugars that yield two molecules of monosaccharides on hydrolysis, a reaction usually catalysed by dilute acid or by a specific enzyme.

Polysaccharides consist of large numbers of monosaccharide units bonded together by glycosidic bonds and are the most common form of carbohydrate found in nature.

Carbohydrates, being widely distributed throughout the plant and animal kingdoms, act mainly in two broad capacities: as energy sources and as structural polymers.

Proteins are the most abundant biomolecules in all living organisms. The term protein is derived from the Greek word 'proteios', meaning primary or holding first place, a name that reflects their cent…

Amino acids are compounds that contain both an amino group and a carboxylic acid group in the same molecule.

Amino acids are classified primarily on the nature of their R group, commonly called the side chain. Based on the chemical character of this side chain, amino acids are grouped as acidic, basic or neu…

Amino acids are colourless, water-soluble crystalline solids. Because each molecule carries both a carboxyl group and an amino group, their acid-base behaviour differs from that of ordinary amines or…

The amino acids that make up a protein are joined together covalently by peptide bonds. A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of a second amino aci…

Proteins are classified, based on their overall structure (shape), into two major types: fibrous proteins and globular proteins.

Proteins are polymers of amino acids, and their three-dimensional structure depends mainly on the sequence of amino acids (the residues) making up the chain.

Each protein has a unique three-dimensional structure held together by interactions such as disulphide bonds, hydrogen bonds, and hydrophobic and electrostatic interactions.

Proteins are the functional units of living things and play a vital role in essentially all biological processes.

A great many biochemical reactions occur continuously inside living cells: the digestion of food and the harvesting of energy from it, and the synthesis of the many molecules required for various cell…

Enzymes are biocatalysts that catalyse one specific biochemical reaction. In general, an enzyme speeds up its reaction by reducing the activation energy of that reaction, achieved by stabilising the h…

Lipids are organic molecules that are soluble in organic solvents such as chloroform and methanol, and insoluble in water. The word 'lipid' is derived from the Greek word 'lipos', meaning fat.

Based on their structures, lipids are classified as simple lipids, compound lipids and derived lipids.

Lipids serve a wide range of biological roles. (1) Lipids are an integral component of the cell membrane and are necessary for the structural integrity of the cell.

Vitamins are small organic compounds that cannot be synthesised by our body but that are essential for certain body functions; because the body cannot make them itself, they must be obtained through t…

Vitamins are classified into two groups based on their solubility, either in water or in fat.

The inherent characteristics of each and every species are transmitted from one generation to the next.

Nucleic acids are biopolymers of nucleotides. Controlled hydrolysis of either DNA or RNA yields three types of component: a nitrogenous base, a pentose sugar and a phosphate group.

In the early 1950s, Rosalind Franklin and Maurice Wilkins used X-ray diffraction to unravel the structure of DNA.

Ribonucleic acids are similar in overall composition to DNA, but cells contain up to eight times as much RNA as DNA.

In addition to their well-known role as the structural subunits of the nucleic acids, nucleotides carry out a variety of other, independent functions in every cell.

A hormone is an organic substance (for example a peptide or a steroid) that is secreted by one tissue, enters the bloodstream, and induces a physiological response (for example growth or a change in m…

Sample papers and previous-year board questions for this subject.