Biomolecules Class 12 Chemistry Exam Questions

Please refer to the below Biomolecules important questions for Class 12 Chemistry. These questions and answers have been prepared as per the latest NCERT Book for Class 12 Chemistry. Students should go through chapter wise Class 12 Chemistry Important Questions designed as per the latest examination pattern issued by CBSE.

Short Answer Questions :

Question. Which one of the following is a monosaccharide :
starch, maltose, fructose, cellulose
Answer : Fructose is a monosaccharide because it cannot be hydrolysed to simpler polyhydroxy aldehydes or ketones.

Question. Write such reactions and facts about glucose which can not be explained by open chain structure. 
Answer : The following reactions of D-glucose cannot be explained on the basis of its open chain structure :
(i) D-Glucose does not react with sodium bisulphite (NaHSO₃).
(ii) It does not give 2, 4-DNP test and Schiff’s test.
(iii) The pentaacetate of D-glucose does not react with hydroxylamine.
(iv) D-Glucose shows the phenomenon of mutarotation, i.e., when its aqueous solution is kept for sometime its optical activity changes.
(v) On reaction with 1 mole of methanol, it yield two monomethyl derivatives which are known as methyl a-D-glucoside and methyl-b-Dglucoside.

Question. When RNA is hydrolysed, there is no relationship among the quantities of different bases formed. What does this fact suggest about the structure of RNA? 
Answer : When a RNA molecule is hydrolysed then there is no relationship between the quantities of four bases viz. adenine (A), guanine (G), cytosine (C), and uracil (U). This fact suggests that RNA has single stranded structure.

Question. Define the following term :
Invert sugar 
Answer : An equimolar mixture of glucose and fructose, obtained by hydrolysis of sucrose in presence of an acid or the enzyme invertase is called invert sugar.

Question. List two characteristic features of enzymes.
Answer : (i) Enzymges are highly specific for a particular reaction and for a particular substrate.
(ii) Very small amount of enzyme is required for the process of a reaction.

Question. What is meant by ‘reducing sugars’?
Answer : Carbohydrates which reduce Tollen’s reagent are reducing sugars. All monosaccharides, aldoses or ketoses are reducing sugars.

Question. Define the following term :
Nucleoside 
Answer : Nucleoside contains pentose sugar, and base whereas nucleotide contains pentose sugar, base as well as phosphate group.
Nucleoside = Base + Sugar
Nucleotide = Base + Sugar + Phosphate.

Question. Name the deficiency diseases resulting from lack of Vitamins A and E in the diet.
Answer : Vitamin – A : Night blindness Vitamin E : Muscular weakness.

Question. Amino acids may be acidic, alkaline or neutral, How does this happen? What are essential and non-essential amino acids? Name one of each type. 
Answer : Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecules.
(a) Equal number of amino and carboxyl groups makes it neutral (b) more number of amino groups than carboxyl groups make it basic and (c) more carboxyl groups as compared to amino groups make it acidic.
Amino acids which cannot be synthesised in the body and must be obtained through diet are known as essential amino acids, e.g., valine and leucine. There are ten essential amino acids. Amino acids which can be synthesised in the body are known as non-essential amino acids, e.g., alanine and glutamic acids.

Question. Write the main structural difference between DNA and RNA. Of the two bases, thymine and uracil, which one is present in DNA?
Answer : Structural differences between DNA and RNA
(i) The sugar in DNA is deoxyribose while that in RNA is ribose.
(ii) DNA has a double-stranded helical structure, while RNA has a single-stranded helical structure.
Functional differences between DNA and RNA
(i) DNA is the chemical basis of heredity and is responsible for maintaining the identity of different species.
(ii) RNA molecules are responsible for protein synthesis but the message for the synthesis of a particular protein is present in DNA.
In DNA, thymine is present.

Question. Name of the purines present in DNA. 
Answer : Adenine and guanine

Question. Write the name of vitamin whose deficiency causes bone deformities in children.
Answer : Vitamin D

Question. Name two water soluble vitamins, their sources and diseases caused due to their deficiency in diet. 
Answer : Examples of water soluble vitamins :
Vitamin B and vitamin C.

Question. Write the name of the vitamin whose deficiency causes bleeding of gums. 
Answer : Vitamin C

Question. (a) What is the structural difference between a nucleoside and a nucleotide?
(b) The two strands in DNA are not identical but are complementary. Explain.
Answer : (a) Nucleoside contains pentose sugar, and base whereas nucleotide contains pentose sugar, base as well as phosphate group.
Nucleoside = Base + Sugar
Nucleotide = Base + Sugar + Phosphate.
(b) DNA is a double helix in which the two strands of DNA are held by the hydrogen bonds between the bases on the two strands. Thymine (T) pairs with adenine through two hydrogen bonds and cytosine
(C) pairs with guanine (G) through three H–bonds. Hence, the two strands of DNA are complementary to each other.

Question. Name the bases present in RNA. Which one of these is not present in DNA? 
Answer : The bases present in RNA are adenine (A), guanine (G) cytosine (C) and Uracil (U).
Uracil is not present in DNA

Question. Differentiate between fibrous proteins and globular proteins. What is meant by the denaturation of a protein?
Answer : Characteristic differences between globular and fibrous proteins can be given as :

Denaturation : The loss of biological activity of a protein by changing the pH, temperature or by adding some salt due to disruption of the native structure of protein is called denaturation.
During denaturation secondary and tertiary structure of protein is destroyed but primary structure remains intact.

Question. What is the structural feature characterising reducing sugar? 
Answer : The reducing sugars have free aldehydic or ketonic groups.

Question. Name the products of hydrolysis of sucrose. Why is sucrose not a reducing sugar?
Answer : (i) Glucose and fructose.

Sucrose is not a reducing sugar because reducing groups of glucose and fructose are involved in glycosidic bond formation.

Question. The deficiency of which vitamin causes the disease, ‘pernicious anaemia’?
Answer : Vitamin B₁₂

Question. (a) Write the important structural difference between DNA and RNA.
(b) Mention the names of the bases produced on hydrolysis of DNA.
Answer : (a) Structural differences between DNA and RNA
(i) The sugar in DNA is deoxyribose while that in RNA is ribose.
(ii) DNA has a double-stranded helical structure, while RNA has a single-stranded helical structure.
Functional differences between DNA and RNA
(i) DNA is the chemical basis of heredity and is responsible for maintaining the identity of different species.
(ii) RNA molecules are responsible for protein synthesis but the message for the synthesis of a particular protein is present in DNA. (Structural difference).
(b) DNA an hydrolysis gives pentose sugar, Phosphoric acid and nitrogen containing heterocyclic bases viz. adenine, guanine, cytosine and thymine.

Question. Define the following term :
Vitamins 
Answer : Organic compounds required in the diet in small amounts to perform specific biological functions for normal maintainance of optimum growth and health of the organism are called vitamins.

Question. Name two fat soluble vitamins, their sources and the diseases caused due to their deficiency in diet. 
Answer : Examples of fat soluble vitamins are vitamin A and D.

Question. What is a glycosidic linkage?
Answer : The two monosaccharides are joined together by an oxide linkage formed by the loss of water molecule. Such linkage is called glycosidic linkage.

Question. What is meant by biocatalysts? 
Answer : Substances which catalyse chemical reactions taking place in living organisms are called biocatalysts. e.g., enzymes

Question. How are the vitamins classified? Mention the chief sources of vitamins A and C. 
Answer : Vitamins are classified into two groups depending upon their solubility in water or fat.
(i) Fat soluble vitamins.
(ii) Water soluble vitamins.
Sources of vitamin A : Fish, liver oil, carrots, butter and milk.
Sources of vitamin C : Citrus fruits, amla and green leafy vegetables.

Question. Describe the following terms in reference of proteins :
(i) Primary structure
(ii) Denaturation 
Answer : (i) Primary structure : The specific sequence in which the various amino acids present in a protein are linked to one another is called its primary structure. Any change in the primary structure creates a different protein.
Secondary structure : The conformation of the polypeptide chain is known as secondary structure. The two types of secondary structure are a-helix and b-pleated sheet structure.
In a-helix structure, the polypeptide chain forms all the possible hydrogen bonds by twisting into a right handed screw (helix) with the —NH groups of each amino acid residue hydrogen bonded to the >C=O group of an adjacent turn of the helix. In b-pleated sheet structure, all peptide chains are stretched out to nearly maximum extension and then laid side by side which are held together by intermolecular hydrogen bonds.
(i) Denaturation : The loss of biological activity of a protein by changing the pH, temperature or by adding some salt due to disruption of the native structure of protein is called denaturation.
During denaturation secondary and tertiary structure of protein is destroyed but primary structure remains intact.

Question. Which of the two components of starch is water soluble? 
Answer : Amylose is water soluble and amylopectin is insoluble in water.

Question. B-complex is an often prescribed vitamin. What is complex about it and what is its usefulness?
Answer : B-complex is a group of vitamins which contains vitamins B₁, B₂, B₆, B₁₂, biotin, folic acid, pantothenic acid and nicotinic acid. It is required to release energy from food and to promote healthy skin and muscles. Its deficiency causes beri beri and pernicious anaemia.

Question. Mention one important function of nucleic acids in our body. 
Answer : DNA is reserve of genetic information and responsible for heredity transmission.

Question. (a) What type of bonding helps in stabilising of a-helix structure of proteins?
(b) Differentiate between globular and fibrous proteins. 
Answer : (a) Hydrogen bonding
(b) Characteristic differences between globular and fibrous proteins can be given as :

Question. Name the deficiency disease resulting from lack of vitamin A in the diet.
Answer : Vitamin – A : Night blindness Vitamin E : Muscular weakness.

Question. Write the structural and functional difference between DNA and RNA. 
Answer : Structural differences between DNA and RNA
(i) The sugar in DNA is deoxyribose while that in RNA is ribose.
(ii) DNA has a double-stranded helical structure, while RNA has a single-stranded helical structure.
Functional differences between DNA and RNA
(i) DNA is the chemical basis of heredity and is responsible for maintaining the identity of different species.
(ii) RNA molecules are responsible for protein synthesis but the message for the synthesis of a particular protein is present in DNA.

Question. Deficiency of which vitamin causes nightblindness?
Answer : Vitamin A

Question. Define the following terms as related to proteins :
(i) Peptide linkage
(ii) Primary structure
(iii) Denaturation
Answer : (i) This is called peptide linkage or peptide bond e.g.,

(ii) Primary structure : The specific sequence in which the various amino acids present in a protein are linked to one another is called its primary structure. Any change in the primary structure creates a different protein.
Secondary structure : The conformation of the polypeptide chain is known as secondary structure. The two types of secondary structure are a-helix and b-pleated sheet structure.
In a-helix structure, the polypeptide chain forms all the possible hydrogen bonds by twisting into a right handed screw (helix) with the —NH groups of each amino acid residue hydrogen bonded to the >C=O group of an adjacent turn of the helix. In b-pleated sheet structure, all peptide chains are stretched out to nearly maximum extension and then laid side by side which are held together by intermolecular hydrogen bonds.
(iii) Denaturation : The loss of biological activity of a protein by changing the pH, temperature or by adding some salt due to disruption of the native structure of protein is called denaturation.
During denaturation secondary and tertiary structure of protein is destroyed but primary structure remains intact.