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A. Give the structure… (Class 12 Chemistry SQP 2024-25, Q25)

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ChemistryCBSE Class 12 · Sample paper, session 2024-25 · 3 marks · Short answer

CBSE Class 12 Chemistry sample paper 2024-25: question 25

From the official CBSE sample question paper for 2024-25, section C, question 25, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 3 marks · Short answerBiomolecules

a. Give the structure of all the possible dipeptides formed when the following two amino acids form a peptide bond. (2)
Alanine
Glycine
b. Keratin, insulin, and myosin are a few examples of proteins present in the human body. Identify which type of protein is keratin and insulin and differentiate between them based on their physical properties. (1)

Figure in the paper: Structures of alanine () and glycine () drawn in skeletal form. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

Open one hint at a time and try again before the next.

Hint 1

A peptide bond forms between the –COOH of one amino acid and the –NH₂ of the other.

Hint 2

Swap which amino acid supplies the –COOH to get the second dipeptide.

Hint 3

Proteins are classified by shape into fibrous and globular. Link the shape to water solubility.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (a) Two dipeptides are possible, depending on which amino acid gives its –COOH to the peptide bond (–CO–NH–).
    Ala–Gly (alanylglycine):

    1 mark

  2. Gly–Ala (glycylalanine):

    1 mark

  3. (b) Keratin is a fibrous protein. Its polypeptide chains lie side by side, held by H-bonds and disulphide links, giving a fibre-like structure. It is generally insoluble in water.

    ½ mark

  4. Insulin is a globular protein. Its chains coil to give a spherical shape, and it is generally soluble in water.

    ½ mark

Answer: (a) Ala–Gly: H₂N–CH(CH₃)–CO–NH–CH₂–COOH and Gly–Ala: H₂N–CH₂–CO–NH–CH(CH₃)–COOH; (b) keratin fibrous (water-insoluble), insulin globular (water-soluble)

Where the marks are

  • Structure of Ala–Gly (1 mark)
  • Structure of Gly–Ala (1 mark)
  • Keratin is fibrous and insoluble in water (½ mark)
  • Insulin is globular and soluble in water (½ mark)

Revise the chapter

  • Chapter: Biomolecules (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Biomolecules, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.