NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules- It is fascinating to know that the living systems (like humans, plants, animals) are made up of non-living atoms and molecules. These molecules can be very complex as well as simple in nature and are simply known as biomolecules for eg. Carbohydrates, Proteins, Lipids and Nucleic acids, etc. The NCERT solutions for class 12 chemistry chapter 14 biomolecules deals with characteristics, functions, and structures of biomolecules. The basic definition of biomolecules is that they are the chemicals that are produced by living organisms to sustain life, promote growth and reproduce. It is an important and very basic chapter of biochemistry which you may study in your higher classes. Although this chapter will involve cramming you need not worry as you will get all NCERT solutions for class 12 chemistry chapter 14 biomolecules here.
This chapter holds 4 marks in the CBSE Board exams. In this chapter, there are a total of 8 topic wise questions and 25 questions in the exercise. The NCERT solutions for class 12 chemistry chapter 14 Biomolecules are presented in a very comprehensive manner. These NCERT solutions help students in their preparation of CBSE boards exams as well as in the competitive exams like NEET, JEE Main, etc. After completing the NCERT solutions for class 12 chemistry chapter 14 Biomolecules you will be able to explain the characteristics of biomolecules like proteins, carbohydrates, and nucleic acid; classify proteins, carbohydrates, nucleic acid, and vitamins on the basis of their structures; describe the role of biomolecules in biosystem and also able to explain difference between RNA and DNA. By referring to the NCERT solutions for class 12 , students can understand all the important concepts and practice questions well enough before their examination.
Important points of NCERT solutions for Class 12 Chemistry Chapter 14 Biomolecules
- Carbohydrates and proteins are essential constituents of our food.
- Carbohydrates are optically active polyhydroxy molecules or ketones or aldehydes. Carbohydrates are classified into 3 groups- monosaccharides, disaccharides, and polysaccharides.
- Proteins are the polymers of 20 different -amino acids. These amino acids are linked by peptide bonds.
- Vitamins additional food factors required in the diet.
Topics and Sub-topics of NCERT Class 12 Chemistry Chapter 14 Biomolecules
14.5 Nucleic Acids
NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules Exercises 14.1 to 14.8
Question 14.3 How do you explain the absence of aldehyde group in the pentaacetate of D-glucose?
When pentaacetate of glucose is made to react with hydroxylamine , it does not react indicating the absence of free —CHO group.
In aqueous solution, the cyclic structure (have -OH group at C-1 ) should get converted to open chain structure which has an aldehyde group at C-1. It then should react with hydroxylamine and give glucose oxime. But such case is not observed. This suggests that in aqueous solution open chain structure doesn't exist and as a result, the aldehyde group is absent in pentaacetate of glucose.
Question 14.4 The melting points and solubility in water of amino acids are generally higher than that of the corresponding halo acids. Explain.
Amino acids have both acidic and basic group(amine) which lead to the formation of zwitterions and make them dipolar compounds. Due to this property, they form strong molecular bonds themselves and also with water. This result high melting point and good solubility in water as compared to haloacids.
Halo acids doesn't exhibit the property of dipolar compounds. Only carboxyl group of haloacid is involved in H-bonding, not the halogen atom. That's why they have low melting points and less solubility than amino acids.
Question 14.5 Where does the water present in the egg go after boiling the egg?
Due to denaturation of proteins, globules unfold and helix gets uncoiled which changes its biological activity. In denaturation, secondary and tertiary structures are destroyed whereas primary structure remains the same.
Due to this process (denaturation of proteins) coagulation of egg take place while boiling. In egg, the globular protein changes into a rubber-like structure which is responsible for absorption of water.
Question 14.6 Why cannot vitamin C be stored in our body?
Vitamin C is a water-soluble vitamin which is excreted from the body in the form of urine and cannot be stored. So they must be supplied in the diet regularly.
Question 14.1 What are monosaccharides?
Monosaccharides are the carbohydrates that cannot be hydrolysed further to give simpler units of polyhydroxy aldehyde or ketone. Nearly 20 monosaccharides are known to occur in nature. The general formula of monosaccharides is where, n =3 to 7. Some common examples of monosaccharides are glucose, fructose.
Question 14.2 What are reducing sugars?
The carbohydrate which can reduce Fehling’s solution and Tollens’ reagent is referred to as reducing sugar. Also, all monosaccharides whether ketose or aldose are reducing sugars.
Question 14.6 What is glycogen? How is it different from starch?
Glycogen is a polysaccharide carbohydrate which is stored in the body of animals or human beings. Whenever our body requires glucose (energy), glycogen breaks down to glucose with the help of the enzyme. It is present in liver, brain and muscles. Whereas starch is a polysaccharide carbohydrate stored in plants.
Question 14.8 What is the basic structural difference between starch and cellulose?
Cellulose is a long straight-chain polysaccharide made of - D - glucose units and has 1,4 - glycoside linkage.
Whereas starch is made up of 2 components:- Amylose and amylopectin.
Amylose is a long straight chain made of - D - glucose units and joined by 1,4 - glycosidic linkage.
Amylopectin is a branched structure and chains are formed at 1,4 - glycoside linkage and branching occurs at 1.6 - glycosidic linkage.
Question 14.10 Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.
Below are the few reactions which cannot be explained by the open structure of glucose:-
1. Even if glucose has an aldehyde group, it does not give Schiff’s test and as a result, it does not form the hydrogen sulphite addition product with NaHSO 3 .
2. The pentaacetate of glucose does not react with hydroxylamine, which indicates the absence of free —CHO group.
3. It is found that glucose exists in two different crystalline forms which are named as α and β. This property can only be explained by the cyclic structure of glucose.
Question 14.11 What are essential and non-essential amino acids? Give two examples of each type.
The amino acids which are required for the body and can be synthesised in the body are known as non-essential amino acids. E.g Glycine, Alanine. Whereas, the amino acids which are required for our body but cannot be synthesised by our body and should be taken through diet are known as essential amino acids. E.g. Valine, Leucine
Question 14.12(i) Define the following as related to proteins
i) Peptide linkage
Peptide linkage is an amide bond formed between –COOH group and –NH 2 group. The reaction between two molecules of either different or similar amino acids proceeds by the combination of the amino group of one molecule with the carboxyl group of the other molecule. This will result in the elimination of a water molecule and formation of a peptide bond –CO–NH–.
Question 14.12(ii) Define the following as related to proteins
(ii) Primary structure
Primary structure of proteins: Each and every polypeptide present in a protein has amino acids linked with each other in a specific sequence and it is this sequence of amino acids that are known to be the primary structure of that protein. Any change in this primary structure that is, the sequence of amino acids creates a different protein.
Question 14.12(iii) Define the following as related to proteins
When a protein in its raw form, is subjected to change like change in temperature e.g boiling in hot water or chemical change like a variation in pH, the hydrogen bonds are disturbed. This results in unfolding of globules and uncoiling of the helix and thus protein loses its biological activity. This is called denaturation of the protein .
Question 14.13 What are the common types of secondary structure of proteins?
Secondary structures of proteins are found to exist in two types of structure:-
(i) Helix structure:- α-Helix is a way in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right-handed screw or helix with the –NH group of each amino acid and residue hydrogen bonded to the of an adjacent turn of the helix.
(ii) pleated sheet:- In this structure, all peptide chains are stretched out to maximum extension and then laid side by side which is held together by strong intermolecular hydrogen bonds.
Question 14.15 Differentiate between globular and fibrous proteins .
The difference between fibrous protein and globular protein is given below :-
| Fibrous Protein || Globular Protein |
| When the polypeptide chains run parallel and are held together with the help of hydrogen and disulphide bonds. || In case of a globular protein, the chains of polypeptides coil around and give a spherical shape |
| These proteins are generally insoluble in water. || These proteins are generally soluble in water. |
| E.g. keratin, myosin || E.g., Insulin, albumins |
Question 14.16 How do you explain the amphoteric behaviour of amino acids?
Amino acid has both acidic group and basic group . Thus in aqueous solution, the carboxyl group can lose a proton and the basic group (amine group) can accept a proton. In this way, it forms zwitter ion which can act in both ways i.e., acidic as well as basic. Hence amino acids are amphoteric in nature.
Question 14.17 What are enzymes?
Enzymes are the biocatalysts i.e., they catalyse biological reactions. Enzymes are very specific in nature and a particular enzyme can be used for a particular substrate. They are generally named after the name of a compound on which they act. For e.g conversion of maltose to glucose requires enzyme maltase.
Question 14.18 What is the effect of denaturation on the structure of proteins?
In denaturation of protein, globules get unfolded and helix gets uncoiled and also globular protein converts into fibrous protein. The primary structure remains the same but secondary and tertiary structure of the protein are destroyed so its biological activity changes.
Question 14.19 How are vitamins classified? Name the vitamin responsible for the coagulation of blood.
On the basis of their solubility in water vitamins are classified as:-
- Water-soluble vitamins:- Water soluble vitamins such as Vitamin C need to taken through diet regularly as they are excreted in the form of urine.
- water-insoluble and fat-soluble vitamin:- Since these vitamins are not soluble in water so we don't need to take them regularly through diet. They are stored in liver and adipose. E.g. Vitamin D
Vitamin K is responsible for the coagulation of blood.
Question 14.21 What are nucleic acids? Mention their two important functions.
Nucleic acids are biomolecules found in nuclei of a cell. They are of two types
(i) DNA - Deoxyribonucleic acid
(ii) RNA - Ribonucleic acid.
The two important functions of nucleic acid are:-
(i) DNA present in chromosomes is responsible for heredity by transferring genes.
(ii) Both the nucleic acids are responsible for the protein synthesis in a cell.
Question 14.22 What is the difference between a nucleoside and a nucleotide?
| Nucleoside || Nucleotide |
| 1. It has base and sugar. || 1. It has base, sugar and phosphoric acid. |
| 2. The base is attached to 1 ' position of sugar. |
| 2. In this, the base is attached to 1' positon and phosphoric acid to 5' position of sugar moiety. |
Question 14.23 The two strands in DNA are not identical but are complementary. Explain.
The two strands in DNA are not identical but they held together because they form hydrogen bonds with each other. So they are not identical but complementary to each other. Cytosine forms a hydrogen bond with guanine and adenine forms a hydrogen bond with thymine. SO, that's why the two strands act as a complementary for each other.
Question 14.24 Write the important structural and functional differences between DNA and RNA.
Structural differences between DNA and RNA:-
(i) The sugar moiety in DNA is D-2-deoxyribose whereas sugar moiety in RNA is D-ribose.
(ii) DNA contains thymine but it is absent in RNA.
(iii) The helical structure of DNA is double-stranded whereas it is single-stranded in case of RNA.
Functional differences between DNA and RNA:- The main function of DNA is to provide heredity but the main function of RNA is a synthesis of protein in a cell.
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