CBSE Class 12 Chemistry Biomolecules Question Bank Set A

Question. Glucose reacts with hydroxylamine to form an oxime. This confirms the presence of
a) straight chain of six carbon atoms
b) carbonyl group
c) primary alcoholic group
d) secondary alcoholic group
Answer. B

Question. The symbols D and L in the name of Carbohydrate represents
a) Dextro rotatory nature
b) Laevo rotatory nature
c) The relative configuration of a particular isomer
d) The optical activity of compounds
Answer. C

Question. Which of the following is incorrect for glucose?
a) It contains four >CHOH groups.
b) It contains one –CH₂OH group.
c) It contains one –CHO group.
d) It contains one >C=O group.
Answer. D

Question. To which position of sugar moiety, nucleoside is linked to phosphoric acid in a nucleotide?
a) 2’
b) 3’
c) 4’
d) 5’
Answer. D

Question. Vitamin A is
a) Retinol
b) Ascorbic acid
c) Thiamine
d) Calciferol
Answer. A

Question. Which sugar is present in RNA?
a) Glucose
b) Fructose
c) D-Ribose
d) D-2-Deoxyribose
Answer. D

Question. Which of the following amino acid is neutral?
a) Aspartic acid
b) Glycine
c) Lysine
d) Arginine
Answer. B

Question. A secondary structure of protein is stabilized by
a) H-bond
b) peptide bond
c) ionic bond
d) disulphide bond
Answer. A

Question. How many amino acids are present in insulin?
a) 25
b) 20
c) 51
d) 52
Answer. C

Question. Nucleotides are joined together by
a) Glycosidic linkage
b) Peptide linkage
c) Hydrogen bonding
d) Phosphodiester linkage
Answer. D

ASSERTION REASON TYPE QUESTIONS
Answer the following questions selecting the appropriate option given below:
a) Assertion and reason both are correct statements and reason is correct explanation for assertion
b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
c) Assertion is correct, but reason is incorrect statement
d) Assertion is incorrect, but reason is correct statement

Question. Assertion: Sucrose is a non-reducing sugar.
Reason: Sucrose has glycosidic linkage.
Answer. B

Question. Assertion: Glucose reacts with hydroxylamine to form an oxime and also adds a molecule of hydrogen cyanide to give cyanohydrin.
Reason: The carbonyl group is present in the open chain structure of glucose.
Answer. A

Question. Assertion: Deoxyribose, C₅H₁₀O₄ is a carbohydrate.
Reason: Carbohydrates are hydrates of carbon so compounds which follow Cx(H₂O)y formula are carbohydrates.
Answer. C

Question. Assertion: Keratin is a globular protein.
Reason: Enzymes are globular proteins.
Answer. D

Question. Assertion: The two strands of DNA are complementary.
Reason: Cytosine always pairs with guanine and thymine pairs with adenine.
Answer. A

CASE BASED QUESTIONS

Amino acids are building blocks of proteins. More than 300 amino acids have been described, but only 20 amino acids take part in protein synthesis. Amino acids are necessary for protein synthesis and have various functions in the body. It is necessary to take them in the diet because their deficiency results in decrease formation of protein or protein is not formed as a result protein deficiency may occur. It is concluded that amino acids play important role in our body. All α-amino acids exist as zwitter ions each of which has a specific isoelectric point. Above isoelectric point, a α-amino acid exists as an anion. Two or three or many α-amino acids join together to form di- or tri- or polypeptides or proteins respectively.

Question. In proteins, α-amino acids are joined together by
a) phosphodiester linkage
b) glycosidic linkage
c) peptide linkage
d) hydrogen bonding
Answer. C

Question. Which of the following α-amino acids is not optically active?
a) Leucine
b) Valine
c) Alanine
d) Glycine
Answer. D

Question. The correct structure of the dipeptide gly-ala is
a) H₂N-CH₂-CO-NH-CH₂-COOH
b) H₂N-CH(CH₃)-CO-NH-CH₂-COOH
c) H₂N-CH₂-CO-NH-CH(CH₃)-COOH
d) H₂N-CH₂-CO-NH-CH(CH₂SH)-COOH
Answer. C

Question. Which of the following amino acids is an essential amino acid?
a) Glycine
b) Valine
c) Alanine
d) Glutamic acid
Answer. B

Question. α-amino acid at its isoelectric point exists as
a) H₃N⁺ – CHR – COO-
b) H₂N – CHR – COOH
c) H₂N – CHR – COO-
d) H₃N⁺ – CHR – COOH
Answer. A

SHORT ANSWER TYPE QUESTIONS

Question. Name the sugar present in milk. How many monosaccharide units are present in it? What are such oligosaccharides called?
Answer. Lactose is present in milk. It has 2 monosaccharide units. They are glucose and galactose. These are called disaccharides.

Question. What is the effect of denaturation on the structure of proteins?
Answer. During denaturation, the protein molecules uncoil from an ordered and specific conformation into a more random confirmation. Denaturation does not change the primary structure of protein but results from arrangement of secondary and tertiary structures.

Question. Where does the water present in the egg go after boiling the egg?
Answer. When an egg is boiled in water, the water present in egg is used in denaturation of protein probably through H-bonding.

Question. Which one of the following is a disaccharide: Starch, Maltose, fructose, glucose?
Answer. Maltose

Question. Name two water soluble vitamins, their sources and diseases caused due to their deficiency.
Answer. Vitamin C, Vitamin B
Sources: milk, pulses. wheat bran, sea food, yeast etc deficiency diseases: Beri-Beri

Question. What are enzymes?
Answer. The enzymes are biological catalysts produced by living cells which catalyse the biochemical reactions. Without enzymes,the living process would be very slow to sustain life. All enzymes are proteins.

Question. Write a reaction which shows that all the carbon atoms in glucose are linked in a straight chain.
Answer. When glucose is heated with HI and red P, at 1000C for a long period, it gives n-hexane.
CH₂OH(CHOH)₄CHO ------------------ CH₃(CH₂)₄CH₃

Question. What are the products of hydrolysis of maltose.?
Answer. GLUCOSE, it gives two molecules of glucose.
C₁₂H₂₂O₁₁ + H₂O → 2 C₆H₁₂O₆

Question. (i)Which one of the following is a disaccharide: starch, maltose, fructose, glucose?
(ii) What is the difference between acidic amino acid and basic amino acid?
(iii) Write the name of the linkage joining two nucleotides.
Answer.
(i) Maltose
(ii) Acidic amino acid contains 2 carboxylic acids groups and 1 amino group. Basic amino acids contain 2 amino and one —COOH group.
(iii) Phospho diester linkage.

Question.Classify the following as monosaccharides disaccharides and polysaccharides- Glucose, Sucrose, maltose, ribose, glycogen, lactose, fructose.
Answer. 
Monosaccharide          Disaccharides       Polysaccharides
Glucose                      Sucrose               Glycogen
Fructose                     Maltose
Ribose                        Lactose

Question. Write the sequence of bases in the complementary strand of the given strand –
A G G C T T A A C C T
Answer. The sequence of bases in the complementary sequence is –
T C C G A A T T G G A

Question. Name the forces responsible for secondary and tertiary structure.
Answer. The forces which are responsible for tertiary structure of proteins are hydrogen bonds, disulphide linkage, vanderwalls and electrostatic forces of attraction.

Question. Why cannot vitamin C be stored in our body?
Answer.  Vitamin C cannot be stored in our body because it is water soluble. As a result, it is readily excreted in the urine.

Question. What are reducing sugars?
Answer. Reducing sugars are carbohydrates that reduce Fehling’s solution and Tollen’s reagent. All monosaccharides and disaccharides, excluding sucrose, are reducing sugars.

Question. Write two main functions of carbohydrates in plants.
Answer. Two main functions of carbohydrates in plants are:
(i) Polysaccharides such as starch serve as storage molecules.
(ii) Cellulose, a polysaccharide, is used to build the cell wall.

Question. What is the difference between a glycosidic linkage and a peptide linkage?
Answer. Glycosidic linkage is the linkage that joins two monosaccharides through an oxygen atom (-O-). Peptide linkage is the linkage that joins two amino acids through -CONH- bond.

Question. What is the difference between Nucleotide and Nucleoside?
Answer. The molecules in which one of the nitrogen bases (purines or pyrimidine) is bonded with a sugar molecule (ribose or deoxyribose) is a nucleoside. The nucleoside linked with the phosphate group is called a nucleotide.

Question. Glucose does not give 2, 4-DNP test and Schiff’s test. Why?
Answer. Glucose has a cyclic structure in which the -CHO group is not free because it forms a hemiacetal linkage with the -OH group at C-5. Therefore, it does not give 2, 4-DNP test although it has -CHO group. 

Question. How would you explain the amphoteric behaviour of amino acids?
Answer. In a single molecule, amino acids have both an acidic (carboxyl group) and a basic (amino group). They neutralise each other in aqueous solutions. A proton is released by the carboxyl group, whereas it is accepted by the amino group. Amino acids react with both acids and bases in their zwitterionic form, displaying amphoteric behaviour.

Question. The two strands in DNA are not identical but complementary. Explain.
Answer. Despite the fact that the two strands of DNA are not similar, they are joined together through hydrogen bonds. Adenine and cytosine create hydrogen bonds with thymine and guanine, respectively. As a consequence, the two strands function as a complement to one another.

LONG ANSWER TYPE QUESTIONS:

Question. Which sugar is called invert sugar? Why is it called so?
Answer. Sucrose is called invert sugar. The sugar obtained from sugar beet is a colourless, crystalline and sweet substance. It is very soluble in water and its aqueous solution is dextrorotatory. On hydrolysis with dilute acids or enzyme invertase, cane sugar gives equimolar mixture of D-(+)-GLUCOSE and D-(-)- FRUCTOSE. So, sucrose is dextrorotatory but after hydrolysis gives dextrorotatory glucose and laevorotatory fructose. Since there is change in the sign of rotation from dextro before hydrolysis to laevo after hydrolysis , the reaction is called inversion reaction and the mixture is called invert sugar.

Question. Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.
Answer. (i) Despite having aldehyde group, glucose does not give Schiff test and 2,4-DNP test.
(ii)Glucose does not react with sodium hydrogen bisulphite to form addition product.
(iii)The pentaacetate of glucose does not react with hydroxyl amine showing the absence of free -CHO group.

Question. What happens when D-glucose is treated with the following reagents? (i) HI (ii) Bromine water (iii) HNO₃
Answer. (i) when glucose is treated with HI, it forms n-hexane.
(ii) when glucose is treated with Bromine water, gluconic acid is formed.
(iii) when glucose is treated with nitric acid, Saccharic acid is formed.

Question. Define the following as related to proteins (i)Peptide linkage (ii) Primary structure (iii) Denaturation.
Answer. (i)Peptide linkage- Peptide bond is formed by the condensation of two or more, same or different α-amino acids. -CO -NH- linkage is called peptide linkage.
(ii) Primary structure- Primary structure of proteins give the sequence in which amino acids are linked in one or more polypeptide chains of proteins.
(iii) Denaturation- A process that changes the physical and biological properties without affecting the chemical composition of a protein is called denaturation. The denaturation is caused by certain physical or chemical treatments such as in pH, temperature, presence of some salts or certain chemical agents.

Question. Differentiate the following :
(i) Globular and fibrous proteins. (ii) Nucleoside and a nucleotide.
Answer. (i) Fibrous proteins: They are long and thread like and tend to lie side by side to form fibers. In some cases, they are held together by hydrogen bonds at many points. These proteins serve as a chief structural material of animal tissues. Examples, keratin, collagen Globular proteins: The molecules of these proteins are folded into compact units and form spheroid shapes. Intermolecular forces are weak. These proteins are soluble in water or aqueous solution of acids, bases or salts. Globular proteins make up all enzymes, hormones, fibrinogen etc. Examples, hemoglobin, insulin
(ii) The nitrogenous base and a pentose sugar are called as nucleosides. The nitrogenous base, a pentose sugar and a phosphate group are called as nucleotides.

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