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Karnataka 2nd PUC Chemistry Question Bank Chapter 14 Biomolecules
2nd PUC Chemistry Biomolecules NCERT Textbook Questions
What are monosaccharides?
The simplest carbohydrates which cannot be decomposed into smaller products are known as monosaccharides. the simple carbohydrates which cannot be hydrolysed into still simpler compounds. About twenty different monosaccharides occur in nature. Monosaccharides are generally crystalline solids, sweet in taste and soluble in water. Their solubility in water is due to extensive hydrogen bonding between water molecules and the -OH groups present in the molecules.
What are reducing sugars?
Reducing sugars are carbohydrates which reduce Fehling solution to red precipitate of CH2O and Tollen’s reagent to shining metallic silver. All monosaccharides (both aldoses and ketoses) and disaccharides, except sucrose, are reducing sugar. Thus, D-(+)- glucose, D – (+) galactose, D-(-) fructose, D-(+) -maltose and D-(+) -lactose are reducing sugars.
Write two main functions of carbohydrates in plants.
- Cell walls of plants are made up of cellulose.
- In the form of starch, carbohydrates act as storage molecules in plants.
- Classify the following into monosaccharides and disaccharides.
- Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose.
- Monosaccharides: Ribose, 2-deoxyribose, fructose.
- Disaccharides: maltose, galactose, lactose.
What do you understand by the term glycosidic linkage?
The oxygen linkage through which two monosaccharides are joined together by the loss of a water molecule to form a molecule of disaccharide is called the glycosidic linkage. The glycosidic linkage in maltose molecule is shown below.
What is glycogen? How is it different from starch?
Glycogen is a condensation polymer of α-D glucose. Starch is not a single compound but is a mixture of two components—a water-soluble component called amylase (15- 20%) and water-insoluble component amylopectin (80 – 85%). Amylose is a linear polymer of α – D – glucose. But both glycogen and amylopectin are branched polymers of α – D – glucose; father glycogen is more highly branched than amylopectin as amylopectin chains consist of 20 – 25 glucose units, glycogen chains consist of 10 – 14 glucose units.
What are the hydrolysis products of
(i) sucrose and (ii) lactose?
Both sucrose and lactose are disaccharides sucrose on hydrolysis give one molecule of α – D glucose and one molecule of β – D – fructose but lactose on hydrolysis give one molecule of β – D glucose and one molecule of β – D galactose.
What is the basic structural difference between starch and cellulose?
The basic difference between starch and cellulose lies in the nature of the glucose molecules present. Starch consists of two compounds i.e., amylose and amylopectin. In both of them, α-D(+) glucose molecules are present Amylose contains linear chains of these molecules linked in a C1-C4 manner. In amylopectin, these linear chains are further linked in a C1-C6 manner. In cellulose, β-D(+) glucose molecules are linked to one another in a C1-C4 manner. Thus, starch and cellulose have different arrangements of constituents.
What happens when D-glucose is treated with the following reagents?
(ii) Bromine water
Enumerate the reactions of D-glucose which cannot be explained by its open-chain structure.
(a) D (+) – the glucose does not undergo certain characteristic reactions of aldehydes, e.g., glucose does not form NaHSO3 addition product.
(b) Glucose reacts with NH2OH to form an oxime but glucose pentaacetate does not. This implies that the aldehydic group is absent in glucose pentaacetate.
(c) D – (+) – glucose exists in two stereoisomeric forms, i.e., α -glucose and β-glucose.
(d) Both α – D – glucose, and β – D – glucose undergo mutarotation in an aqueous solution. Although the crystalline forms of α- and β -D (+) – glucose are quite stable in an aqueous solution but each form slowly changes into an equilibrium mixture of both.
(e) D (+) – glucose forms two isomeric methyl glucosides. Aldehydes normally react with two moles of methanol per mole of the aldehyde to form an acetal but D (+) – glucose when treated with methanol in presence of dry HCl gas, reacts with only one mole of methanol per mole of glucose to form a mixture of two methyl D – glucosides i. e., methyl – α – D – glucoside (melting point 43 8 K, specific rotation +158°) and methyl – β – D – glucoside (melting point 308 K, specific rotation – 33°).
What are essential and non-essential amino acids? Give two examples of each type.
Essential amino acids are those which the body fails to synthesise e.g. valine (val) and leucine (Leu). Non-essential amino acids are the acids which are synthesised by the body e.g. glycine (Gly) and alanine (Ala).
Define the following as related to proteins
1. Peptide linkage
2. Primary structure
1. Peptide linkage: Proteins are condensation polymers of α – amino acids in which the same or different α – amino acids are connected by peptide bonds. Chemically, a peptide bond is an amide linkage formed between – COOH group of one a – amino acid and – NH2 group of the other α – amino acid by loss of a molecule of water. Example
2. Primary structure: Proteins may contain one or more polypeptide chains. Each polypeptide chains has a large number of α – amino acids which are linked to one another in a specific sequence. The specific sequence in which the various α – amino acids present in a protein are linked to one another is called its primary structure. Any change in the sequence of α – amino acids creates a different protein.
3. Denaturation: Each protein in the biological system has a unique 3-D structure and has specific biological activity. This is called the native form of the protein. When a protein in its native form is subjected to physical changes like change in temperature, pH etc. hydrogen bonds are broken. Due to the cleavage of hydrogen bonds, the unfolding of the protein molecule takes place and it loses its biological activity.
This loss of biological activity is called Denaturation. During denaturation 2° and 3° structures are destroyed but the 1° structure remains intact. As a result of denaturation, globules proteins are converted into fibrous proteins. In other words, denaturation leads to coagulation. That is why coagulated proteins are called denaturated proteins. Example boiling of the egg causes coagulation of egg white.
What are the common types of secondary structures of proteins?
The conformations which the polypeptide chains assume as a result of hydrogen bonding is called the secondary structure of proteins. The two types of secondary structures are α -helix and β -pleated sheet structure.
α -helix structure:- In this structure, the -NH group of an amino acid residue forms H-bonds with the > c = o group of the adjacent turn of the right-handed screw. (α – helix)
β – pleated sheet structure:- This structure is called so because it looks like the pleated folds of a drapery. In this structure, all the peptide chains are stretched out to nearly the maximum extension and then laid side by side. These peptide chains are held together by intermolecular hydrogen bonds.
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 the
group of the adjacent turns of the α – helix help in stabilising the helix.
Differentiate between global and fibrous proteins.
|Fibrous protein||Gloublar protein|
|1. It is a fibre like structure formed by the polypeptide chain. these proteins are held together by strong hydrogen and disulphide bonds||1. The polypeptide chain in the protein is folded around itself, giving rise to a spherical structure|
|2. It is insoluble in water||2. It is usually soluble in water|
|3. Fibrous protein usually used, for example, keratin it Present in nails and hair collagen in undoms, and myosin in muscles.||3. All enzymes are globular proteins. some hormone such as insulin are also globular proteins|
How do you explain the amphoteric- behaviour of amino acids?
In an aqueous solution, the carboxyl group of an amino acid can lose a proton and the amino group can accept a proton to give a dipolar ion known as a zwitterion
Therefore, in zwitterion form, the amino acid can both an acid and a base.
Thus, amino acids show amphoteric behavior.
What are enzymes?
The enzyme is 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 sometimes after the particular reaction.
For example, The enzymes used to catalyse the hydrolysis of maltose into glucose are named malase.
Again, the enzymes used to catalyse the oxidation of one substrate with the simultaneous reduction of another substrate are named oxidoreductase enzymes. The name of the enzyme ends with 4-ase’.
What is the effect of denaturation on the structure of proteins?
During denaturation, 2° and 3° structures of proteins are destroyed but the 1° structure remains intact. As a result of denaturation, die globular proteins (soluble in H2O) are converted into fibrous proteins (insoluble in H2O) and their biological activity is lost. For example, a boiled egg which contains coagulated proteins cannot be hatched.
How are vitamins classified? Name the vitamin responsible for the coagulation of blood.
Vitamins are broadly classified as water-soluble and water-insoluble. Apart from these, they have been classified on the basis of the composition. Vitamin K is responsible for blood clotting.
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). 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.
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 acid are.
- DNA is responsible for the transmission of inherent characters from one generation to the next. This process of transmission is called heredity.
- Nucleic acids- (both DNA and RNA) are responsible for protein synthesis in the cell. Even though the proteins are actually synthesized by the. various RNA molecules in a cell, the message for the synthesis of a particular protein is present in DNA.
What is the difference between a nucleoside and a nucleotide?
A nucleoside is formed by the attachment of the base to l’ position of the 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.
Two nucleic acid chains are wound about each other and held together by hydrogen bonds between pairs of bases. The trends are complementary to each other because the hydrogen bonds are formed between specific pairs of bases. Adenine forms hydrogen bonds with thymine whereas cytosine forms hydrogen bonds with guanine.
Write the important structural and functional differences between DNA and RNA.
The structural differences between DNA and RNA are as follows:
|1. The sugar moiety in DNA molecules is β-D- deoxyribose.||1. The sugar moiety in RNA molecules is β-D- ribose.|
|2. DNA consists of Thymine(T), it does not contain uracil (U)||2. RNA consists of 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 difference between DNA and RNA are as follows:
|1. DNA is the chemical basis of heredity||1. RNA is not responsible for heredity|
|2. DNA molecules do not synthesized proteins, but not transfer coded message for the synthesis of proteins||2. proteins are synthesized by RNA molecules in the cells.|
What are the different types of RNA found in the cell?
Three types of RNA are present in the cell. These are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (t-RNA).
2nd PUC Biomolecules Additional Questions
What are the expected products of hydrolysis of lactose?
Lactose is a disaccharide on hydrolysis, it gives two molecules of monosaccharides, i.e. one molecule of each of D – (+) galactose.
Fresh tomatoes are a litter source of vitamin C than those which have been stored for some -time. Explain.
On prolonged exposure to air, vitamin C present in tomatoes is destroyed due to aerial oxidation.
Name the vitamin responsible for poor coagulation of blood due to deficiency.
Ka and Kb values of α – amino acids are very low. Explain. +
The Ka and Kb values of α – amino acids, the acidic group is -NH3 instead of -COOH in carboxylic acids and the basic group is -COO instead of NH2 group in aliphatic amines.
Two samples of DNA, A and B have melting temperature (Tm) 340 and 350k respectively. Can you draw any conclusion from these data regarding their base content?
We know that CG base pair has 3 H-bonds and AT base pair has two H-bonds, therefore CG base pair is more stable than AT base pair. Since B has higher melting point than A, B has higher CG content compared to A.
Which polysaccharide is stored in the liver of animals?
What is a prosthetic group?
A prosthetic group is a non-protein portion obtained by hydrolysis of conjugated proteins. The main function of the prosthetic group is to control the biological functions of proteins.
Name two carbohydrates which can act as biofuels.
starch and glycogen.
B – complex is an often prescribed vitamin. What is complex about it and what is its usefulness?
It is a group of vitamins which contains vitamins B1 B2, B6, B12, biotin, pantothenic acid, folic acid and nicotinic acid. Since it is not a single vitamin, but a group of vitamins, it is called vitamin B – complex. It is required to release energy from food and to promote healthy skin and muscles. Its deficiency causes beriberi (vit. B1 and pernicious anaemia (vit. B12).
Glucose forms an oxime but glucose pentaacetate does not. Explain.
Glucose reacts with NH2OH via open-chain form which has the free – CH = O group to form glucose oxime. Glucose pentaacetate, on the other hand, cannot be converted into the open-chain form because its anomeric hydroxyl group (C1 – OH) is acetylated and hence does not form the oxime.