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CBSE Class 12th Chemistry Notes for Chapter 14 Biomolecules


  • Carbohydrates are optically active polyhydroxy aldehydes or ketones or molecules which provide such units on hydrolysis. They are broadly classified into three groups: monosaccharides, disaccharides and polysaccharides.


  • Glucose, the most important source of energy for mammals, is obtained by the digestion of starch. Monosaccharides are held together by glycosidic linkages to form disaccharides or polysaccharides.


  • Proteins are the polymers of about twenty different ∝- amino acids which are linked by peptide bonds. Ten amino acids are called essential amino acids because they cannot be synthesised by our body, hence must be provided through diet.


  • Proteins perform various structural and dynamic functions in the organisms. Proteins which contain only ∝- amino acids are called simple proteins.


  • The secondary or tertiary structure of proteins gets disturbed on change of pH or temperature and they are not able to perform their functions. This is called denaturation of protein.


  • Enzymes are the biocatalysts that speed up the reactions in biosystems. They are very specific and selective in their actions and chemically all enzymes are proteins.


  • Vitamins are accessory food factors required in the diet. They are classified as fat soluble (A, D, E and K) and water soluble (B group and C). Deficiency of vitamins leads to many serious diseases.


  • Nucleic acids are polymers of nucleotides which in turn consist of a base, a pentose sugar and phosphate moiety. Nucleic acids are responsible for the transfer of characters from parents to offsprings. There are two types of nucleic acids: DNA and RNA. DNA contains a five carbon sugar molecule called 2-deoxyribose whereas RNA contains ribose.

Both DNA and RNA contain adenine, guanine and cytosine. The fourth base in DNA is thymine and in RNA is uracil. The structure of DNA is a double strand whereas RNA is a 

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