NCERT Solutions for Class 12 Chemistry Part 1 Chapter 14
Biomolecules Class 12
Chapter 14 Biomolecules Exercise Solutions
In text : Solutions of Questions on Page Number : 412
Glucose or sucrose are soluble in water but cyclohexane or benzene (simple six membered ring compounds) are insoluble in water. Explain.
A glucose molecule contains five -OH groups while a sucrose molecule contains eight -OH groups. Thus, glucose and sucrose undergo extensive H-bonding with water.
Hence, these are soluble in water.
What are the expected products of hydrolysis of lactose?
How do you explain the absence of aldehyde group in the pentaacetate of D-glucose?
But pentaacetate of D-glucose does not react with NH2OH. This is because pentaacetate does not form an open chain structure.
The melting points and solubility in water of amino acids are generally higher than that of the corresponding halo acids. Explain.
Due to this dipolar behaviour, they have strong electrostatic interactions within them and with water. But halo-acids do not exhibit such dipolar behaviour.
Where does the water present in the egg go after boiling the egg?
Why cannot vitamin C be stored in our body?
What products would be formed when a nucleotide from DNA containing thymine is hydrolysed?
When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained. What does this fact suggest about the structure of RNA?
A DNA molecule is double-stranded in which the pairing of bases occurs. Adenine always pairs with thymine, while cytosine always pairs with guanine. Therefore, on hydrolysis of DNA, the quantity of adenine produced is equal to that of thymine and similarly, the quantity of cytosine is equal to that of guanine.
Exercise : Solutions of Questions on Page Number : 423
What are monosaccharides?
Monosaccharides are carbohydrates that cannot be hydrolysed further to give simpler units of polyhydroxy aldehyde or ketone.
What are reducing sugars?
Write two main functions of carbohydrates in plants.
Two main functions of carbohydrates in plants are:
(i) Polysaccharides such as starch serve as storage molecules.
(ii)
Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose
Monosaccharides:
Ribose, 2-deoxyribose, galactose, fructose Disaccharides:
What do you understand by the term glycosidic linkage?
Glycosidic linkage refers to the linkage formed between two monosaccharide units through an oxygen atom by the loss of a water molecule.
What is glycogen? How is it different from starch?
Glycogen is a carbohydrate (polysaccharide). In animals, carbohydrates are stored as glycogen.
Starch is a carbohydrate consisting of two components - amylose (15 - 20%) and amylopectin (80 - 85%).
What are the hydrolysis products of (i)sucrose and (ii)lactose?
(i)
(ii) The hydrolysis of lactose gives β-D-galactose and β-D-glucose.
What is the basic structural difference between starch and cellulose?
Amylopectin is a branched-chain polymer of 𝖺-D-glucose units, in which the chain is formed by C1-C4 glycosidic linkage and the branching occurs by C1-C6 glycosidic linkage.
What happens when D-glucose is treated with the following reagents?
Answer :
(i)
(ii) When D-glucose is treated with Br2 water, D- gluconic acid is produced.
(iii)
Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.
(1) Aldehydes give 2, 4-DNP test, Schiff's test, and react with NaHSO4to form the hydrogen sulphite addition product. However, glucose does not undergo these reactions.
(2) The pentaacetate of glucose does not react with hydroxylamine. This indicates that a free -CHO group is absent from glucose.
(3)
What are essential and non-essential amino acids? Give two examples ofeach type.
Essential amino acids are required by the human body, but they cannot be synthesised in the body. They must be taken through food. For example: valine and leucine
Define the following as related to proteins
Answer :
The primary structure of protein refers to the specific sequence in which various amino acids are present in it, i.e., the sequence of linkages between amino acids in a polypeptide chain. The sequence in which amino acids are arranged is different in each protein. A change in the sequence creates a different protein.
In a biological system, a protein is found to have a unique 3-dimensional structure and a unique biological activity. In such a situation, the protein is called native protein. However, when the native protein is subjected to physical changes such as change in temperature or chemical changes such as change in pH, its H-bonds are disturbed. This disturbance unfolds the globules and uncoils the helix. As a result, the protein loses its biological activity. This loss of biological activity by the protein is called denaturation. During denaturation, the secondary and the tertiary structures of the protein get destroyed, but the primary structure remains unaltered.
What are the common types of secondary structure of proteins?
There are two common types of secondary structure of proteins:
(i) 𝖺-helix structure
(ii) β-pleated sheet structure
What type of bonding helps in stabilising the 𝖺-helix structure of proteins?
The H-bonds formed between the -NH group of each amino acid residue and
Differentiate between globular and fibrous proteins.
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Fibrous protein |
Globular protein |
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1. |
It is a fibre-like structure formed by the polypeptide chain. These proteins are held together by strong hydrogen and disulphide bonds. |
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The polypeptide chain in this protein is folded around itself, giving rise to a spherical structure. |
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It is usually insoluble in water. |
2. |
It is usually soluble in water. |
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Fibrous proteins are usually used for structural purposes. For example, keratin is present in nails and hair; collagen in tendons; and myosin in muscles. |
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All enzymes are globular proteins. Some hormones such as insulin are also globular proteins. |
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Q16 :
Answer :
Therefore, in zwitter ionic form, the amino acid can act both as an acid and as a base.
What are enzymes?
Enzymes are proteins that catalyse biological reactions. They are very specific in nature and catalyse only a particular reaction for a particular substrate. Enzymes are usually named after the particular substrate or class of substrate and some times after the particular reaction.
Again, the enzymes used to catalyse the oxidation of one substrate with the simultaneous reduction of another substrate are named as oxidoreductase enzymes.
What is the effect of denaturation on the structure of proteins?
How are vitamins classified? Name the vitamin responsible for thecoagulation of blood.
On the basis of their solubility in water or fat, vitamins are classified into two groups.
(i) Fat-soluble vitamins: Vitamins that are soluble in fat and oils, but not in water, belong to this group. For example:
Vitamins A, D, E, and K
(ii) Water-soluble vitamins:Vitamins that are soluble in water belong to this group. For example: B group vitamins (B1, B2, B6, B12, etc.) and vitamin C
However, biotin or vitamin H is neither soluble in water nor in fat. Vitamin K is responsible for the coagulation of blood.
Why are vitamin A and vitamin C essential to us? Give their important sources.
The deficiency of vitamin A leads to xerophthalmia (hardening of the cornea of the eye) and night blindness. The deficiency of vitamin C leads to scurvy (bleeding gums).
What are nucleic acids? Mention their two important functions.
Nucleic acids are biomolecules found in the nuclei of all living cells, as one of the constituents of chromosomes. There are mainly two types of nucleic acids - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids are also known as polynucleotides as they are long-chain polymers of nucleotides.
Two main functions of nucleic acids are:
(i) DNA is responsible for the transmission of inherent characters from one generation to the next. This process of transmission is called heredity.
(ii)
What is the difference between a nucleoside and a nucleotide?
A nucleoside is formed by the attachment of a base to position of sugar. Nucleoside = Sugar + Base
On the other hand, all the three basic components of nucleic acids (i.e., pentose sugar, phosphoric acid, and base) are present in a nucleotide.
Nucleotide = Sugar + Base + Phosphoric acid
The two strands in DNA are not identical but are complementary. Explain.
Write the important structural and functional differences between DNA and RNA.
The structural differences between DNA and RNA are as follows:
DNA |
RNA |
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1. |
The sugar moiety in DNA molecules is β-D-2 deoxyribose. |
1. |
The sugar moiety in RNA molecules is β-D-ribose. |
2. |
DNA contains thymine (T). It does not contain uracil (U). |
2. |
RNA contains uracil (U). It does not contain thymine (T). |
3. |
The helical structure of DNA is double-stranded. |
3. |
The helical structure of RNA is single- stranded. |
The functional differences between DNA and RNA are as follows:
DNA |
RNA |
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DNA is the chemical basis of heredity. |
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RNA is not responsible for heredity. |
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DNA molecules do not synthesise proteins, but transfer coded |
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Proteins are synthesised by RNA |
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message for the synthesis of proteins in the cells. |
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molecules in the cells. |
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What are the different types of RNA found in the cell?
(i) Messenger RNA (m-RNA)
(ii) Ribosomal RNA (r-RNA)
(iii) Transfer RNA (t-RNA)