CBSE 2025 · Region 6 · Set 1 · Q30 · 4 marks
The $\displaystyle \alpha$-amino acids are the building blocks of proteins. All $\displaystyle \alpha$-amino acids exist as zwitter ion due to which they show amphoteric behaviour. All amino acids are joined through peptide bond. Proteins are broadly classified as globular proteins and fibrous proteins. Globular proteins are water soluble, whereas fibrous proteins are not. The complete structure of protein is discussed at four different levels i.e. primary, secondary, tertiary and quaternary structures. Protein loses its biological activity in denatured form.(a)Define the following :(i)Peptide linkage(ii)Denatured protein(b)Why do amino acids show amphoteric behaviour ?(c)How can you differentiate between Fibrous protein and Globular protein ?(ii)Write the names of two different secondary structures of proteins.
The $\displaystyle \alpha$-amino acids are the building blocks of proteins. All $\displaystyle \alpha$-amino acids exist as zwitter ion due to which they show amphoteric behaviour. All amino acids are joined through peptide bond. Proteins are broadly classified as globular proteins and fibrous proteins. Globular proteins are water soluble, whereas fibrous proteins are not. The complete structure of protein is discussed at four different levels i.e. primary, secondary, tertiary and quaternary structures. Protein loses its biological activity in denatured form.
(a)
Define the following :
(i)
Peptide linkage
(ii)
Denatured protein
(b)
Why do amino acids show amphoteric behaviour ?
(c)
How can you differentiate between Fibrous protein and Globular protein ?
(ii)
Write the names of two different secondary structures of proteins.
Marking-scheme solution
(i)
A linkage which joins amino acids through -CO-NH- bond
(ii)
When a protein in its native form, is subjected to physical change like change in
temperature or chemical change like change in pH, it loses its biological activity.
(b)
Due to zwitter ion formation which can react with both acids and bases./ Due to
the presence of both carboxylic group and amino group.
(i)
Fibrous protein: parallel polypeptide chain structure / insoluble in water
Globular protein: spherical polypeptide chain structure/ soluble in water
(c)
(ii)
α-helix and β-pleated sheet
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CBSE Class 12 Chemistry past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.