CBSE Class 12 Chemistry Biomolecules Questions Answers

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1. Name the sugar present in milk.

A: Lactose,

2. How many monosaccharide units are present in it?

A: two monosaccharide units are present.

3.What are such oligosaccharides called?

A: Such oligosaccharides are called disaccharides

4. How do you explain the presence of all the six carbon atoms in glucose in a Straight chain?

A: On prolonged heating with HI, glucose gives n-hexane.

3. Name the linkage connecting monosaccharide units in polysaccharides.

A: Glycosidic linkage.

4. Under what conditions glucose is converted to gluconic and saccharic acid?

A: Glucose is converted to gluconic acid by bromine water and to saccharic acid by conc. HNO3.

5. Which sugar is called invert sugar?

A: Sucrose.

6. During curdling of milk, what happens to sugar present in it?

A: It converts into Lactic acid.

7. Monosaccharide contain carbonyl group hence are classified, as aldose or ketose. The number of carbon atoms present in the monosaccharide molecule are also considered for classification. In which class of monosaccharide will you place fructose?

A: Fructose is a ketohexose.

8. The letters ‘D’ or ‘L’ before the name of a stereoisomer of a compound indicate the correlation of configuration of that particular stereoisomer. This refers to their relation with one of the isomers of glyceraldehyde. Predict whether the following compound has ‘D’ or ‘L’configuration.  

CBSE Class 12 Chemistry Haloalkanes Haloarenes 5

A: ‘L’ configuration

9. What are constituents of Starch?

A: Amylose and Amylopectin

10. What D N A & R N A Stand for?

A: Deoxy ribonucleic acid and Ribonucleic acid.

11. What are Zwitter ions?

A: A Zwitter ion is a dipolar ion formed by neutralization of acidic and basic centers present within the molecule.

12. .What is non reducing sugar? Give example.

A: The groups like CHO, - C= O, which are not freely available in the molecule do not answer tollens or Fehling’s test are called non reducing sugar. E.g. maltose and lactose

13. Define mutarotation? Give example.

A: The anomers of glucose i.e. alpha and beta are having specific rotation of + 1110and + 19.20 respectively. The mixtures of these two have a rotation of +52.40. this is called a mutarotation.

14. Amino acids are amphoteric in behavior? Explain.

A: they form zwitter ion (dipolar ion) and behave as neutral molecule at pH 7(isoelectric point).


1. Define native state and denaturation of protein. What happens when?

a. Protein is cooled to zero degree C? 

b. Protein is heated to 800 C

A: protein in the native state has definite configuration and biological activity. The higher structure of protein is affected without disturbing the primary structure is called denaturation.

a. no change

b. the coagulation of the protein takes place.

2. Which forces are responsible for stability of alpha Helix of protein? Why it is called 3.613 helix?

A: H-bonding. It has 3.6 amino acids in one single turn, and a 13 member ring is formed by H bonding.

3. What are essential amino acids? Give example and what happens when it is polymerized?

A: amino acids required by the body and cannot be synthesized in our body are called essential amino acids. e.g. Lysine. When it is polymerized polypeptide chains are formed.

4. Glucose and sucrose are soluble in water but Cyclohexane and benzene are not soluble. Why?

A : Glucose and sucrose form H bonding with water

5.(i) Write the sequence of base on mRNA molecule synthesized on the following strand of DNA:



(ii)Name a powerful antioxidant which is a water soluble vitamin.

A: Vitamin C


1. (i)Protein found in a biological system with a unique three-dimensional structureand biological activity is called a native protein. When a protein in its native form,is subjected to a physical change like change in temperature or a chemical changelike, change in pH, denaturation of protein takes place. Explain the cause.

Ans: A(i) Due to physical or chemical change, hydrogen bonds in proteins are disturbed, globules unfold and helix gets uncoiled therefore protein loses its biological activity. This is called denaturation of proteins.

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