CBSE 2026 · Region 3 · Set 1 · Q29 · 4 marks
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. In addition, some simple molecules like vitamins and mineral salts also play an important role in the functions of organisms. All proteins are polymers of $\displaystyle \alpha$-amino acids. Proteins can be classified into two types on the basis of their molecular shape - Fibrous and Globular proteins. Vitamins are accessory food factors required in the diet. They are classified as fat-soluble and water-soluble. Deficiency of vitamins leads to many diseases. Nucleic acids are the polymers of nucleotides which in turn consist of a base, a pentose sugar and phosphate moiety. There are two types of nucleic acids - DNA and RNA. Nucleic acids are responsible for the transfer of characters from parents to offsprings.(a)Write the name of basic building units of proteins and nucleic acids. How can you differentiate between Fibrous and Globular proteins on the basis of their structures ?(b)What products would be formed when a nucleotide from DNA containing thymine is hydrolyzed ?(ii)Write one structural difference between DNA and RNA.(c)Give one example each of a fat-soluble vitamin and a water-soluble vitamin.
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. In addition, some simple molecules like vitamins and mineral salts also play an important role in the functions of organisms. All proteins are polymers of $\displaystyle \alpha$-amino acids. Proteins can be classified into two types on the basis of their molecular shape - Fibrous and Globular proteins. Vitamins are accessory food factors required in the diet. They are classified as fat-soluble and water-soluble. Deficiency of vitamins leads to many diseases. Nucleic acids are the polymers of nucleotides which in turn consist of a base, a pentose sugar and phosphate moiety. There are two types of nucleic acids - DNA and RNA. Nucleic acids are responsible for the transfer of characters from parents to offsprings.
(a)
Write the name of basic building units of proteins and nucleic acids. How can you differentiate between Fibrous and Globular proteins on the basis of their structures ?
(b)
What products would be formed when a nucleotide from DNA containing thymine is hydrolyzed ?
(ii)
Write one structural difference between DNA and RNA.
(c)
Give one example each of a fat-soluble vitamin and a water-soluble vitamin.
Marking-scheme solution
(a)
α - amino acids
Nucleotides
Fibrous protein :- When the polypeptide chains run parallel and are held
together by hydrogen and disulphide bonds, then fibre-like structure is
formed whereas Globular protein is the polypeptide which coil around to
give a spherical Shape.
(b)
Thymine base, a pentose sugar ($\displaystyle 2$-deoxyribose) and phosphoric acid.
(ii)
DNA is double stranded whereas RNA is single stranded.
(c)
Fat soluble : Vitamin. A/D/E/K
Water soluble : Vitamin. B /C
BiomoleculesProteinsUnderstandcase_studymedium
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CBSE Class 12 Chemistry past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.