CBSE 2024 · Region 3 · Set 1 · Q30 · 4 marks
Proteins are the most abundant biomolecules of the living system. Proteins are the polymers of about twenty different $\displaystyle \alpha$-amino acids which are linked by peptide bonds. Ten amino acids are called essential amino acids. In zwitter ionic form, amino acids show amphoteric behaviour as they react both with acids and bases. On the basis of their molecular shape, proteins are classified into two types : Fibrous and Globular proteins. Structure and shape of proteins can be studied at four different levels i.e., primary, secondary, tertiary and quaternary, each level being more complex than the previous one. The secondary or tertiary structure of proteins get disturbed on change of pH or temperature and they are not able to perform their functions. This is called denaturation of proteins. Answer the following questions :(a)What are essential amino acids ?(b)What is meant by zwitter ionic form of amino acids ?(c)Give one example each for Fibrous protein and Globular protein.(ii)What type of linkages hold monomers of proteins together ?What is the structural feature which characterises a reducing sugar ?(ii)What is the structural difference between nucleoside and nucleotide ?
Proteins are the most abundant biomolecules of the living system. Proteins are the polymers of about twenty different $\displaystyle \alpha$-amino acids which are linked by peptide bonds. Ten amino acids are called essential amino acids. In zwitter ionic form, amino acids show amphoteric behaviour as they react both with acids and bases. On the basis of their molecular shape, proteins are classified into two types : Fibrous and Globular proteins. Structure and shape of proteins can be studied at four different levels i.e., primary, secondary, tertiary and quaternary, each level being more complex than the previous one. The secondary or tertiary structure of proteins get disturbed on change of pH or temperature and they are not able to perform their functions. This is called denaturation of proteins. Answer the following questions :
(a)
What are essential amino acids ?
(b)
What is meant by zwitter ionic form of amino acids ?
(c)
Give one example each for Fibrous protein and Globular protein.
(ii)
What type of linkages hold monomers of proteins together ?
What is the structural feature which characterises a reducing sugar ?
(ii)
What is the structural difference between nucleoside and nucleotide ?
Marking-scheme solution
(a)
Amino acids which cannot be synthesised in the body and must be obtained through diet.
(b)
Dipolar ion formation / Ion having both anionic and cationic parts
<smiles>[R]C(N)C(=O)[O-]</smiles>
(c)
Keratin, myosin - Fibrous
Albumin, Insulin - Globular
(ii)
Peptide linkage / structure
Free aldehydic or ketonic group/ Aldehydic (or carbonyl) group is not involved in glycosidic linkage.
(ii)
In nucleotide, phosphate group is attached to $\displaystyle 5$'-position of sugar moiety while phosphate group is absent in nucleoside / Nucleoside consist of a molecule of sugar linked to nitrogenous base Nucleotide consist of a molecule of sugar ,nitrogenous base and phosphoric acid
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CBSE Class 12 Chemistry past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.