Chapter 14: Biomolecules Mock Test
Time: 1 Hour | Maximum Marks: 25
- All questions are compulsory.
- Section A contains Q1 (Multiple Choice) and Q2 (Very Short Answer).
- Section B contains Short Answer Type I questions (2 marks each). Attempt any 4.
- Section C contains Short Answer Type II questions (3 marks each). Attempt any 2.
- Section D contains Long Answer questions (4 marks each). Attempt any 1.
SECTION A
Q1. Select and write the most appropriate answer from the given alternatives: [4 Marks]
-
Which of the following is a non-reducing sugar?
(A) Glucose(B) Maltose(C) Lactose(D) Sucrose
-
When glucose is treated with bromine water, the product formed is:
(A) Saccharic acid(B) Gluconic acid(C) Sorbitol(D) Fructose
-
The linkage that holds amino acids together in a polypeptide chain is:
(A) Glycosidic linkage(B) Phosphodiester linkage(C) Peptide linkage(D) Hydrogen bond
-
The nitrogenous base present in RNA but absent in DNA is:
(A) Adenine(B) Guanine(C) Thymine(D) Uracil
Q2. Answer the following questions in one sentence: [3 Marks]
- Define: Zwitterion.
- Name the two polymeric components of starch.
- What are essential amino acids?
SECTION B
Attempt any FOUR of the following: [8 Marks]
- How is glucose prepared commercially from starch? Write the chemical equation.
- Define carbohydrates. How are they classified based on their behavior towards hydrolysis?
- What is a peptide bond? Write a chemical equation to show its formation.
- Distinguish between DNA and RNA. (Write any 2 points).
- Write a short note on the denaturation of proteins.
SECTION C
Attempt any TWO of the following: [6 Marks]
- Write the chemical reactions of D-glucose with:
- Hydroxylamine ($NH_2OH$)
- Hydrogen iodide ($HI$) with Red Phosphorus
- Dilute Nitric acid ($HNO_3$)
- Distinguish between Globular proteins and Fibrous proteins. (Write any 3 points).
- Explain the secondary structure of proteins. Briefly describe the $\alpha$-helix and $\beta$-pleated sheet structures.
SECTION D
Attempt any ONE of the following: [4 Marks]
- (a) What are nucleosides and nucleotides? How do they differ? [2 Marks]
(b) What happens when D-glucose is treated with acetic anhydride? What does this reaction indicate about the structure of glucose? [2 Marks] - (a) Draw the Haworth projection formulas of $\alpha$-D-glucopyranose and $\beta$-D-glucopyranose. [2 Marks]
(b) What are enzymes? Give one example of an enzyme-catalyzed reaction. [2 Marks]
Solutions & Marking Scheme
SECTION A [7 Marks]
Q1. Multiple Choice Answers:
1. (D) Sucrose [1 Mark. Both anomeric carbons are involved in the glycosidic linkage]
2. (B) Gluconic acid [1 Mark for correct option]
3. (C) Peptide linkage [1 Mark for correct option]
4. (D) Uracil [1 Mark. DNA has Thymine, RNA has Uracil]
Q2. Very Short Answers:
1. Zwitterion:
A dipolar, electrically neutral ion formed by the internal transfer of a proton from the acidic carboxyl group ($-COOH$) to the basic amino group ($-NH_2$) of an amino acid. [1 Mark]
2. Components of starch:
Starch consists of two polymeric components: Amylose (water-soluble, unbranched) and Amylopectin (water-insoluble, branched). [1 Mark]
3. Essential amino acids:
Amino acids which cannot be synthesized in the human body and must be supplied through the diet are called essential amino acids (e.g., Valine, Leucine). [1 Mark]
SECTION B [8 Marks]
Q3. Preparation of Glucose from Starch:
Commercially, glucose is obtained by the acid hydrolysis of starch by boiling it with dilute $H_2SO_4$ at 393 K under a pressure of 2-3 atm. [1 Mark]
$(C_6H_{10}O_5)_n + nH_2O \xrightarrow{H^+, 393 \text{ K, 2-3 atm}} n C_6H_{12}O_6$
(Starch) (Glucose)
Q4. Classification of Carbohydrates:
Definition: Carbohydrates are optically active polyhydroxy aldehydes or polyhydroxy ketones, or compounds which yield such units upon hydrolysis. [1 Mark]
Classification based on hydrolysis: [1 Mark]
- Monosaccharides: Cannot be hydrolyzed further (e.g., Glucose).
- Oligosaccharides: Yield 2 to 10 monosaccharide units on hydrolysis (e.g., Sucrose).
- Polysaccharides: Yield a large number of monosaccharide units on hydrolysis (e.g., Starch, Cellulose).
Q5. Peptide Bond:
An amide linkage ($-CO-NH-$) formed between the carboxyl group of one $\alpha$-amino acid and the amino group of another, with the elimination of a water molecule, is called a peptide bond. [1 Mark]
$H_2N-CH_2-COOH + H_2N-CH(CH_3)-COOH \xrightarrow{-H_2O} H_2N-CH_2-CO-NH-CH(CH_3)-COOH$
(Glycine + Alanine $\rightarrow$ Glycylalanine)
[1 Mark for reaction]Q6. DNA vs RNA (Any 2 points):
| DNA | RNA |
|---|---|
| Sugar present is $\beta$-D-2-deoxyribose. | Sugar present is $\beta$-D-ribose. |
| Contains Thymine (T) as a pyrimidine base. | Contains Uracil (U) instead of Thymine. |
| Double-stranded $\alpha$-helix structure. | Usually single-stranded. |
[1 Mark for each point of distinction. Total 2 Marks]
Q7. Denaturation of Proteins:
When a protein in its native form is subjected to physical change (like heating) or chemical change (like change in pH), the hydrogen bonds are disturbed. This causes the protein globules to unfold and helices to uncoil. [1 Mark]
As a result, the protein loses its biological activity. This is called denaturation. The secondary and tertiary structures are destroyed, but the primary structure remains intact. (e.g., Coagulation of egg white). [1 Mark]
SECTION C [6 Marks]
Q8. Chemical Reactions of D-Glucose:
- (i) With Hydroxylamine ($NH_2OH$): Forms an oxime. Proves presence of a carbonyl group.
$CHO-(CHOH)_4-CH_2OH + NH_2OH \rightarrow CH(=NOH)-(CHOH)_4-CH_2OH + H_2O$ [1 Mark] - (ii) With HI/Red P: Forms n-hexane. Proves all 6 carbons are in a straight chain.
$C_6H_{12}O_6 \xrightarrow{HI / \text{Red P}, \Delta} CH_3-(CH_2)_4-CH_3$ [1 Mark] - (iii) With dilute $HNO_3$: Oxidizes both the aldehyde and primary alcohol groups to form Saccharic acid (Glucaric acid).
$CHO-(CHOH)_4-CH_2OH \xrightarrow{\text{dil. } HNO_3, [O]} HOOC-(CHOH)_4-COOH$ [1 Mark]
Q9. Globular vs Fibrous Proteins:
| Globular Proteins | Fibrous Proteins |
|---|---|
| Polypeptide chains fold upon themselves to give a spherical (3D) shape. | Polypeptide chains run parallel to each other to form fiber-like structures. |
| They are soluble in water and aqueous solutions. | They are insoluble in water. |
| Sensitive to small changes in temperature and pH. | Stable to moderate changes in temperature and pH. |
| Examples: Insulin, Albumin, Enzymes. | Examples: Keratin (hair, wool), Myosin (muscles). |
[1 Mark for each point of distinction. Total 3 Marks]
Q10. Secondary Structure of Proteins:
The secondary structure refers to the shape in which a long polypeptide chain can exist due to regular folding of the backbone. This shape is primarily stabilized by hydrogen bonds between the $-C=O$ and $-NH-$ groups of the peptide bonds. [1 Mark]
- $\alpha$-Helix: The polypeptide chain twists into a right-handed screw (helix). It is stabilized by intramolecular hydrogen bonds between the $-C=O$ of one amino acid and the $-NH-$ group of the fourth amino acid down the chain. [1 Mark]
- $\beta$-Pleated Sheet: The polypeptide chains are stretched out to nearly maximum extension and laid side-by-side. They are held together by intermolecular hydrogen bonds, forming a pleated, sheet-like structure. [1 Mark]
SECTION D [4 Marks]
Q11. (a) Nucleosides vs Nucleotides [2 Marks] (b) Reaction of Glucose with Acetic anhydride [2 Marks]
(a) Nucleosides and Nucleotides:
- Nucleoside: A compound formed by the attachment of a nitrogenous base to the 1' position of a pentose sugar. (Base + Sugar). [1 Mark]
- Nucleotide: A compound formed when a phosphate group is attached to the 5' (or 3') hydroxyl group of the sugar in a nucleoside. (Base + Sugar + Phosphate). Nucleotides are the building blocks of nucleic acids. [1 Mark]
(b) Glucose + Acetic Anhydride:
When D-glucose is treated with an excess of acetic anhydride in the presence of pyridine, it forms Glucose pentaacetate. [1 Mark]
Significance: This reaction confirms the presence of exactly five hydroxyl ($-OH$) groups in the glucose molecule, attached to different carbon atoms (as it forms a stable pentaacetate). [1 Mark]
Q12. (a) Haworth Projections [2 Marks] (b) Enzymes [2 Marks]
(a) Haworth Projections:
$\alpha$-D-glucopyranose
(Anomeric OH is DOWN)
$\beta$-D-glucopyranose
(Anomeric OH is UP)
[1 Mark for each correct Haworth structure].
(b) Enzymes:
Enzymes are highly specific, complex globular proteins that act as biological catalysts, regulating and accelerating biochemical reactions in living organisms. [1 Mark]
Example: Invertase catalyzes the hydrolysis of sucrose into glucose and fructose. [1 Mark]
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