NCERT Class 12 Chemistry Chapter 14 Biomolecules Notes to each chapter is provided in the list so that you can easily browse through different chapters NCERT Class 12 Chemistry Chapter 14 Biomolecules Solutions and select need one. NCERT Class 12 Chemistry Chapter 14 Biomolecules Question Answers Download PDF. NCERT Chemistry Class 12 Solutions.
NCERT Class 12 Chemistry Chapter 14 Biomolecules
Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. NCERT Class 12 Chemistry Chapter 14 Biomolecules Solutions are part of All Subject Solutions. Here we have given NCERT Class 12 Chemistry Part: I, Part: II Notes. NCERT Class 12 Chemistry Chapter 14 Biomolecules Notes, NCERT Class 12 Chemistry Textbook Solutions for All Chapters, You can practice these here.
Biomolecules
Chapter: 14
| Part – II |
1. What are monosaccharides?
Ans: Monosaccharides are also known as simple sugars. A carbohydrate that cannot be hydrolysed further to give a simpler unit of polyhydroxy aldehyde or ketone is called a monosaccharide. The simplest form of sugar, and the basic units that make up all carbohydrates.
2. What are reducing sugars?
Ans: Reducing sugars are carbohydrates that can donate electrons to another molecule, typically containing an aldehyde or ketone group. They are called ‘reducing sugars’ because the presence of the aldehyde group makes them undergo oxidation readily to form carboxylic acid and in the process the reactive reagents are reduced easily.
3. Write two main functions of carbohydrates in plants.
Ans: Two main functions of carbohydrates in plants are:
(i) Energy Storage: Carbohydrates, particularly in the form of starch, store energy for plants, which can be used during periods of low photosynthesis or during growth.
(ii) Structural material: Carbohydrates are a structural component of plant cell walls, with cellulose being the primary structural material.
4. Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose.
Ans: Monosaccharides: Ribose, 2-deoxyribose, galactose, fructose.
Disaccharides: maltose, lactose.
5. What do you understand by the term glycosidic linkage?
Ans: A glycosidic linkage is formed when a glycosyl donor and a glycosyl acceptor bond together, and a water molecule is lost in the process. This bond connects the anomeric carbon of one sugar to a hydroxyl group of another, forming disaccharides or polysaccharides. It plays a crucial role in the structure and function of carbohydrates.
6. What is glycogen? How is it different from starch?
Ans: Glycogen is a polysaccharide. It is a polymer of D-glucose. It stores food in animals and human beings. It is composed of many glucose units linked together by glycosidic bonds. Glycogen is synthesised and stored primarily in the liver and muscle cells.
The differences between glycogen and starch are:
Glycogen is a highly branched complex carbohydrate with a protein centre, starch is composed of two different complex carbohydrates (amylose and amylopectin). Amylose is linear and less abundant, while amylopectin is branched and more abundant in starch’s polysaccharide composition.
7. What are the hydrolysis products of:
(i) sucrose. and
Ans:
(ii) lactose?
Ans:
8. What is the basic structural difference between starch and cellulose?
Ans: The main structural difference between starch and cellulose is the type of linkage between the glucose units that make up each molecule. Starch has α-glycosidic bonds, making it helical and digestible by humans. In contrast, cellulose is a linear polymer wheres starch is a branched chain polymer.
9. What happens when D-glucose is treated with the following reagents?
(i) HI.
Ans:
(ii) Bromine water.
Ans:
(iii) HNO3
Ans:
10. Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.
Ans: The following reactions of D-glucose which cannot be explained by its open chain structure:
(i) The pentaacetate of glucose does not react with hydroxylamine. This indicates that a free CHO group is absent from glucose.
(ii) Mutarotation: The ability of D-glucose to interconvert between α and β anomers in solution, leading to changes in optical rotation, indicates the presence of a cyclic structure.
(iii) When glucose is treated with methanol in presence of dry hydrogen chloride gas, it forms two isomeric monomethyl derivatives known as methyl a-D-glucoside and methyl ẞ-D-glucoside. These glucosides do not reduce Fehling’s solution and also do not react with hydrogen cyanide or hydroxylamine indicating the absence of a free -CHO group.
(iv) Despite having an aldehydic group, glucose does not give Schiff’s test and it does not react with sodium bisulphite and ammonia.
11. What are essential and non-essential amino acids? Give two examples of each type.
Ans: Essential Amino Acids: Those amino acids which are not synthesised by our body are called essential amino acids.
There are nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Non-essential amino acids: They are synthesised by our body. They are also called dNon-essential amino acids. There are eleven non-essential amino acids alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.
12. Define the following as related to proteins:
(i) Peptide linkage.
Ans: Peptide linkage: The amide bond formed when the carboxylic group of one amino acid molecule reacts with the amino group of another amino acid molecule with the elimination of water molecule is called a peptide bond or peptide linkage. The linkage of multiple amino acids through peptide bonds forms a peptide chain, represented as −CO−NH−.
(ii) Primary structure.
Ans: Primary Structure of Protein: The sequence in which the amino acids are arranged in a protein is called the primary structure of protein.
(iii) Denaturation.
Ans: Denaturation: When a protein is subjected to some physical or chemical treatment which disrupts its higher structures without affecting its primary structure, the process is called denaturation. Thus, the protein will lose its biological activity, e.g., on keeping an egg in boiling water for some time, the egg albumin gets denatured. Thus, precipitation occurs which is irreversible.
13. What are the common types of secondary structure of proteins?
Ans: The two most common types of secondary structure in proteins are alpha helices and beta pleated Structure:
Alpha helices: An alpha helix is an element of secondary structure in which the amino acid chain is arranged in a spiral. The linked kinemage displays a single alpha helix from the N-terminal end, resembling the “helical wheel” shown in the figure.
Beta pleated Structure: Beta-Pleated Sheets of Protein is a type of secondary structure of a protein. It consists of various beta strands linked by hydrogen bonds between adjacent strands.
14. What type of bonding helps in stabilising the a-helix structure of proteins?
Ans: In the a-helix configuration, the peptide chain of amino acids coil as a right-handed screw because of the formation of hydrogen bonds between amide groups of the same peptide chain. A common secondary structural element of proteins consisting of a right-handed helix stabilised by internal hydrogen bonds.
15. Differentiate between globular and fibrous proteins.
Ans: Differentiate between globular and fibrous proteins are:
| Globular proteins | Fibrous proteins |
| Less sensitive to changes in pH,temperature,etc. | More sensitive to changes in pH, temperature, etc. |
| They are folded balls like structures. | Their molecules have long thread-like structures. |
| It’s insoluble in water. | It’s soluble in water. |
| They may have three dimensional. | They have helical or sheet structure. |
16. How do you explain the amphoteric behaviour of amino acids?
Ans: If an amino acid is placed in a strong acid solution (pH = 1), the amino group accepts a proton. If an amino acid is placed in a strong basic solution (pH = 11), the carboxylic acid group loses a proton. In this form, amino acids behave both as acids and bases so they are amphoteric in nature.
17. What are enzymes?
Ans: Enzymes are basically proteins that are produced by living organisms to bring about certain metabolic and biochemical reactions in the body. They are biological catalysts that speed up reactions inside the body. Enzymes are made up of amino acids. Enzymes are proteins that act as biological catalysts. Enzymes catalyse reactions at high rates through their active sites.
18. What is the effect of denaturation on the structure of proteins?
Ans: Denaturation of Proteins: Proteins are very sensitive to the action of heat, change of pH, presence of electrolytes and radiations (particularly of short wavelength). Whenever proteins are subjected to such changes in the surroundings, they undergo some structural changes leading to disruption of three dimensional structure. This leads to a permanent loss of protein activity in many cases, as the protein cannot regain its functional structure.
When a protein’s natural structure is altered due to changes in its environment, leading to a loss of its biological function, it’s called protein denaturation. Denaturation does not alter the primary structure, but results from rearrangement of secondary and tertiary structures.
19. How are vitamins classified? Name the vitamin responsible for the coagulation of blood.
Ans: Vitamins are classified as:
Oil or Fat-soluble vitamins: These vitamins are stored in the body’s fatty tissues and can build up to toxic levels if consumed in excess. They include vitamins A,D,E and F are oil ( or fat soluble).
Water-soluble vitamins: These vitamins are not stored in the body and must be consumed regularly. Excess amounts are typically excreted through urine. They include vitamins B and C which are the water soluble vitamins.
20. Why are vitamin A and vitamin C essential to us? Give their important sources.
Ans: (i) The chemical name of vitamin a is retinol.
The sources of vitamin A are fish liver oil, carrots, butter, and milk. The sources of vitamin C are citrus fruits, amla, and green leafy vegetables. It can also be synthesised in the body from carotenoids present in carrots, tomatoes, ripe mangoes etc. Carotenoids are the precursors of vitamin A.
(ii) The chemical name of vitamin C is ascorbic acid.
The sources of vitamin C are Citrus fruits (oranges, lemons), strawberries, kiwi, bell peppers, broccoli, and tomatoes.
21. What are nucleic acids? Mention their two important functions.
Ans: Nucleic acids are naturally occurring chemical compounds that serve as the primary information-carrying molecules in cells. They play a crucial role in guiding protein synthesis. The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
There are two functions of nucleic acids:
(i) Development and reproduction of all forms of life.
(ii) Synthesis of proteins and are responsible for the transfer of genetic information i.e., the hereditary characteristics.
22. What is the difference between a nucleoside and a nucleotide?
Ans: The difference between a nucleoside and a nucleotide are:
| Nucleoside | Nucleotide |
| A nucleoside is made up of a five-carbon sugar and a nucleobase. It’s a structural component of DNA and is involved in many cellular processes. | A nucleotide is made up of a five-carbon sugar, a nucleobase, and one or more phosphate groups. It’s the building block of nucleic acids like DNA and RNA. |
| During their formation, 1-position of the pyrimidine or 9-position of the purine is linked to C, of the sugar (ribose or deoxyribose) by a ẞ-linkage. | These are formed by esterification of one of the hydroxyl groups (usually C-OH of the sugar part) of the nucleoside phosphoric acid. with |
| Involved in processes like energy metabolism and signalling. | Building block of nucleic acids (DNA and RNA), also involved in energy transfer (e.g., ATP). |
23. The two strands in DNA are not identical but are complementary. Explain.
Ans: (i) DNA has double helical structure in which two strands are twisted about each other held in position by H-bonds between the bases.
(ii) The two strands in a DNA molecule are held together by hydrogen bonds between the purine base of one strand and the pyrimidine base of the other and vice versa. Because of the different sizes and geometries of the bases, the only possible pairing in DNA is G (guanine) and C (cytosine) through three H-bonds (i.e., C = G) and between A (adenine) and T (thiamine) through two H-bonds (i.e., A = T). The base-pairing principle ensures complementary, not identical, sequences in DNA strands, where one strand determines the other’s sequence.
24. Write the important structural and functional differences between DNA and RNA.
Ans: The important structural and functional differences between DNA and RNA are:
| DNA | RNA |
| DNA(Deoxyribonucleic acid) is a molecule that contains genetic instructions for the development, functioning, growth, and reproduction of all known organisms and many viruses | RNA is a ribonucleic acid that helps in the synthesis of proteins in our body. This nucleic acid is responsible for the production of new cells in the human body. |
| In DNA, the sugar is deoxyribose. | In RNA the sugar unit is ribose. |
| The bases in DNA are Adenine (‘A’), Thymine (‘T’), Guanine (‘G’) and Cytosine (‘C’). | RNA shares Adenine (‘A’), Guanine (‘G’) and Cytosine (‘C’) with DNA, but contains Uracil (‘U’) rather than Thymine. |
| Uracil is absent in DNA. | Thymine is absent in RNA. |
| DNA is vulnerable to damage by ultraviolet light. | RNA is more resistant to damage from UV light than DNA. |
| Contains thymine (T) as one of the four bases along with adenine (A), guanine (G), and cytosine (C). | Contains uracil (U) in place of thymine, with the same other bases (A, G, C). |
| DNA is double-stranded, forming a double helix. | RNA exists as a single chain. |
25. What are the different types of RNA found in the cell?
Ans: The Different types of RNA found in cells are mRNA, transfer RNA (tRNA), and ribosomal RNA (rRNA).
