CUET UG Chemistry Booster Test - 3 Structure and Proteins and Amino Acids -

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CUET UG Chemistry Booster Test - 3 Proteins and Amino Acids

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Chemistry Booster Test - 3 Proteins and Amino Acids

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QUESTION 1 OF 20

Consider the following statements about the biochemical logic of life processes:
1. A living system sustains itself and is uniquely composed of living atoms.
2. The pursuit of knowledge of chemical processes within living systems falls in the domain of biochemistry.
3. Proteins form the fundamental basis of structure and functions of life.
4. All functional living proteins are structurally polymers of β-amino acids.
Choose the analytically correct combination.

Answer Review

1 Consider the following statements about the biochemical logic of life processes:
1. A living system sustains itself and is uniquely composed of living atoms.
2. The pursuit of knowledge of chemical processes within living systems falls in the domain of biochemistry.
3. Proteins form the fundamental basis of structure and functions of life.
4. All functional living proteins are structurally polymers of β-amino acids.
Choose the analytically correct combination.

A 2 and 3

B 1, 2 and 3

C 3 and 4

D 1 and 4

💡 Short Explanation

�� Biochemistry studies chemical processes in living systems. �� Proteins are fundamental to life processes. �� Living systems are composed of non-living atoms and molecules.

✅ Correct Answer Explanation

Statement 1 is incorrect because living systems are composed of non-living atoms and molecules. Statement 2 is correct because biochemistry deals with the chemical processes occurring within living organisms. Statement 3 is correct because proteins form the structural and functional basis of life. Statement 4 is incorrect because proteins are polymers of α-amino acids, not β-amino acids. Therefore, Statements 2 and 3 are correct.

❓ Why Other Options Are Incorrect

�� Option B includes incorrect Statement 1.
�� Option C includes incorrect Statement 4.
�� Option D contains two incorrect statements.

🎯 Strategy

Used

Statement-Based Analysis

Application:

Evaluate each statement independently.

Final Logic:

Only Statements 2 and 3 are correct.

🧠 Memory Trick

Biochemistry + Proteins = Life

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Introduction to Proteins

2 The systematic naming and origin tracking for biomolecules relies on historical roots. For proteins, the Greek root \"proteios\" conceptually denotes that these molecules are:

A Most abundant in plants

B Sweet tasting to mammals

C Primary or of prime importance to life

D Complex energy storing polymers

💡 Short Explanation

�� The term protein originates from the Greek word \"proteios\". �� Proteios means first or primary. �� It highlights the biological importance of proteins.

✅ Correct Answer Explanation

The word protein is derived from the Greek word \"proteios,\" meaning primary or of prime importance. This reflects the essential role of proteins in living organisms.

❓ Why Other Options Are Incorrect

�� Option A → Not the meaning of proteios.
�� Option B → Unrelated to proteins.
�� Option D → Proteins are not primarily energy-storage molecules.

🎯 Strategy

Used

Direct Recall

Application:

Recall the origin of the term protein.

Final Logic:

Proteios = Primary.

🧠 Memory Trick

Protein = Prime Importance

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Proteins

3 Based on unified atomic mass unit definitions for biomolecules, what is the exact threshold unit mass value differentiating a standard polypeptide from a full protein?

A > 1,000 u

B > 5,000 u

C > 10,000 u

D > 20,000 u

💡 Short Explanation

�� Proteins generally possess larger molecular masses. �� Molecules above 10,000 u are commonly classified as proteins. �� Smaller chains are considered polypeptides.

✅ Correct Answer Explanation

A biomolecule with a molecular mass greater than approximately 10,000 u is generally classified as a protein, whereas smaller chains are often referred to as polypeptides.

❓ Why Other Options Are Incorrect

�� Options A and B are below the accepted threshold.
�� Option D exceeds the commonly cited value.

🎯 Strategy

Used

Parameter Recall

Application:

Identify the standard molecular mass criterion.

Final Logic:

Protein threshold ≈ 10,000 u.

🧠 Memory Trick

Protein = Above 10,000 u

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Proteins and Polypeptides

4 The presence of an asymmetric α-carbon atom in almost all naturally occurring amino acids means they exist predominantly in specific optical configurations. Which configuration is most prevalent in nature?

A D-configuration

B L-configuration

C Meso-form

D Racemic mixture

💡 Short Explanation

�� Most naturally occurring amino acids are optically active. �� They predominantly exist in the L-configuration. �� Glycine is an exception because it is achiral.

✅ Correct Answer Explanation

Almost all naturally occurring amino acids possess an asymmetric α-carbon and occur predominantly in the L-configuration.

❓ Why Other Options Are Incorrect

�� Option A → Less common in proteins.
�� Option C → Amino acids are generally not meso compounds.
�� Option D → Natural proteins do not contain racemic mixtures.

🎯 Strategy

Used

Concept Recall

Application:

Identify the predominant stereochemical form.

Final Logic:

Natural amino acids are mainly L-amino acids.

🧠 Memory Trick

Life Uses L-Amino Acids

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Optical Activity of Amino Acids

5 Match the common amino acid (List-I) with its standard 1-letter biochemical code symbol (List-II).

List I	List II
1. — Glycine	a. — L
2. — Alanine	b. — V
3. — Valine	c. — G
4. — Leucine	d. — A

A 1-c, 2-d, 3-b, 4-a

B 1-a, 2-b, 3-c, 4-d

C 1-d, 2-c, 3-a, 4-b

D 1-b, 2-a, 3-d, 4-c

💡 Short Explanation

�� Glycine → G �� Alanine → A �� Valine → V �� Leucine → L

✅ Correct Answer Explanation

Matching: 1. Glycine → G 2. Alanine → A 3. Valine → V 4. Leucine → L Therefore: 1-c, 2-d, 3-b, 4-a

❓ Why Other Options Are Incorrect

�� The code assignments are incorrect.

🎯 Strategy

Used

Match the Following

Application:

Recall one-letter amino acid codes.

Final Logic:

Glycine-G, Alanine-A, Valine-V, Leucine-L.

🧠 Memory Trick

G-A-V-L

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Amino Acids

6 Analytically, a patient suffering from a dietary deficiency of essential amino acids cannot internally substitute them because:

A They completely lack the necessary carboxyl group to react.

B The human body lacks the required intrinsic biochemical pathways to synthesise them.

C They instantly form unreactive zwitter ions in the blood.

D They are immediately denatured by stomach acid before absorption.

💡 Short Explanation

�� Essential amino acids cannot be produced adequately by the body. �� They must be obtained through diet.

✅ Correct Answer Explanation

Essential amino acids are termed essential because humans lack the metabolic pathways required to synthesize them in sufficient amounts.

❓ Why Other Options Are Incorrect

�� Option A → False.
�� Option C → Zwitter ion formation is unrelated.
�� Option D → Amino acids are absorbed after digestion.

🎯 Strategy

Used

Concept Application

Application:

Identify the basis of essentiality.

Final Logic:

No synthesis pathway = Essential amino acid.

🧠 Memory Trick

Essential = Must Eat

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Essential Amino Acids

7 Arrange the following biologically important amino acids in decreasing order of the relative number of carboxyl groups compared to amino groups per molecule:
A. Aspartic acid
B. Alanine
C. Arginine

A A, B, C

B . C, B, A

C . B, A, C

D A, C, B

💡 Short Explanation

Aspartic acid is acidic.
Alanine is neutral.
Arginine is basic.

✅ Correct Answer Explanation

Decreasing relative abundance of carboxyl groups:

Aspartic acid > Alanine > Arginine

Thus:

A → B → C

❓ Why Other Options Are Incorrect

They do not follow acidic → neutral → basic order.

🎯 Strategy

Ordering

Application:

Compare acidic, neutral, and basic amino acids.

Final Logic:

Acidic > Neutral > Basic.

🧠 Memory Trick

Aspartic → Alanine → Arginine

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Classification of Amino Acids

8 What fundamental reaction type dictates the chemical classification of an amino acid as an amphoteric species when placed in either strongly acidic or basic media?

A Acid-Base Neutralisation

B Free radical substitution

C Electrophilic addition

D Dehydration synthesis

💡 Short Explanation

�� Amino acids react with both acids and bases. �� They can accept or donate protons. �� This is acid-base behavior.

✅ Correct Answer Explanation

The amphoteric nature of amino acids arises from their ability to undergo acid-base neutralisation reactions because they contain both amino and carboxyl groups.

❓ Why Other Options Are Incorrect

�� Option B → Not involved.
�� Option C → Not characteristic of amino acids.
�� Option D → Related to peptide formation.

🎯 Strategy

Used

Concept Analysis

Application:

Identify the reaction responsible for amphoteric behavior.

Final Logic:

Amphoteric nature results from acid-base reactions.

🧠 Memory Trick

Amino Acid = Acid + Base

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Amphoteric Nature of Amino Acids

9 A neutral amino acid in its solid state exists primarily as a dipolar ion. This structural feature explains why neutral amino acids behave physically like:

A Volatile simple amines

B Simple liquid carboxylic acids

C High melting point, water-soluble salts

D Low boiling point ethers

💡 Short Explanation

�� Amino acids exist as zwitter ions. �� Ionic compounds have high melting points. �� They are generally water-soluble.

✅ Correct Answer Explanation

The ionic nature of zwitter ions gives amino acids physical properties resembling salts, including high melting points and good water solubility.

❓ Why Other Options Are Incorrect

�� Option A → Amines are usually volatile.
�� Option B → Carboxylic acids do not show salt-like behavior.
�� Option D → Ethers are non-ionic.

🎯 Strategy

Used

Property Analysis

Application:

Relate zwitter ions to physical properties.

Final Logic:

Zwitter ions behave like salts.

🧠 Memory Trick

Zwitter Ion = Salt Properties

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Zwitter Ionic Nature

10 Even though Valine is classified structurally as a neutral amino acid, its aqueous solution can conduct electricity under applied voltage at a non-isoelectric pH because:

A The peptide bonds break down into free radicals.

B The molecule contains a metallic coordinate bond.

C The zwitter ion accepts or loses a proton to become a mobile, net-charged species.

D Valine polymerizes into an insulating macromolecule.

💡 Short Explanation

�� Amino acids can gain or lose protons. �� Charged ions move in solution. �� This allows electrical conduction.

✅ Correct Answer Explanation

At pH values different from the isoelectric point, amino acids exist as positively or negatively charged ions. These mobile ions conduct electricity through the solution.

❓ Why Other Options Are Incorrect

�� Option A → Peptide bonds are absent in free valine.
�� Option B → No metallic bond exists.
�� Option D → Polymerization does not occur.

🎯 Strategy

Used

Concept Application

Application:

Relate pH-dependent ionization to conductivity.

Final Logic:

Charged amino acid ions conduct electricity.

🧠 Memory Trick

Away from pI → Charged → Conducts

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Isoelectric Point and Ionic Forms of Amino Acids

11 Regarding the zwitter ion form of amino acids, which of the following statements is analytically correct?
1. It is formed by intermolecular condensation reactions.
2. It is electrically neutral overall but contains strictly separated positive and negative charges internally.
3. It cannot chemically react with strong acids.
4. It represents the open-chain gaseous form of the amino acid.

A 2 only

B 1 and 2

C 2 and 4

D 1 and 3

💡 Short Explanation

�� Zwitter ions contain both positive and negative charges. �� The overall charge is zero. �� They are formed by internal proton transfer.

✅ Correct Answer Explanation

Statement 1 is incorrect because zwitter ions are formed by internal proton transfer, not condensation. Statement 2 is correct because a zwitter ion contains NH₃⁺ and COO⁻ groups while remaining electrically neutral overall. Statement 3 is incorrect because amino acids react with both acids and bases. Statement 4 is incorrect because the zwitter ion is the predominant ionic form in solution and solid state. Therefore, only Statement 2 is correct.

❓ Why Other Options Are Incorrect

�� Option B includes incorrect Statement 1.
�� Option C includes incorrect Statement 4.
�� Option D contains two incorrect statements.

🎯 Strategy

Used

Statement-Based Analysis

Application:

Evaluate each property of zwitter ions separately.

Final Logic:

Only Statement 2 is correct.

🧠 Memory Trick

Zwitter = Positive + Negative = Net Zero

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Zwitter Ionic Form of Amino Acids

12 The internal dipolar ion formed by internal proton transfer within an amino acid molecule is formally named the:

A Carbonium ion

B Zwitter ion

C Carbanion

D Hydronium ion

💡 Short Explanation

�� Amino acids contain acidic and basic groups. �� Internal proton transfer forms a dipolar ion. �� This ion is called a zwitter ion.

✅ Correct Answer Explanation

A zwitter ion is formed when the amino group accepts a proton from the carboxyl group, producing NH₃⁺ and COO⁻ groups within the same molecule.

❓ Why Other Options Are Incorrect

�� Option A → Positively charged carbon species.
�� Option C → Negatively charged carbon species.
�� Option D → H₃O⁺ ion in aqueous solutions.

🎯 Strategy

Used

Definition Recall

Application:

Identify the dipolar form of amino acids.

Final Logic:

Internal proton transfer forms a zwitter ion.

🧠 Memory Trick

Zwitter = Dipolar Amino Acid

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Zwitter Ions

📄 Passage

Amino acids are usually colourless, crystalline solids. These are water-soluble, high melting solids and behave like salts rather than simple amines or carboxylic acids. This behaviour is due to the presence of both acidic (carboxyl group) and basic (amino group) groups in the same molecule. In aqueous solution, the carboxyl group can lose a proton and the amino group can accept a proton, giving rise to a dipolar ion known as a zwitter ion. This is neutral but contains both positive and negative charges.

Based on the passage, the unexpectedly high melting point of amino acids is directly attributed to:

A Their existence as volatile hydrocarbon gases

B Their salt-like, dipolar zwitter ionic physical nature

C Their ability to form strong external peptide bonds in solid state

D The complete lack of reactive functional groups

💡 Short Explanation

�� Amino acids exist as ionic species. �� Ionic compounds generally possess high melting points. �� Zwitter ions behave like salts.

✅ Correct Answer Explanation

The zwitter ionic form contains oppositely charged groups within the same molecule, producing strong electrostatic attractions similar to those found in salts. This results in high melting points.

❓ Why Other Options Are Incorrect

�� Option A → Amino acids are crystalline solids.
�� Option C → Peptide bonds are not responsible here.
�� Option D → Amino acids contain reactive groups.

🎯 Strategy

Used

Passage-Based Analysis

Application:

Relate physical properties to ionic structure.

Final Logic:

Salt-like zwitter ions explain the high melting point.

🧠 Memory Trick

Zwitter Ion = Salt Properties

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Physical Properties of Amino Acids

📄 Passage

Based on the passage, a zwitter ion is considered electrically \"neutral\" overall because:

A It naturally loses all of its valence electrons.

B It contains absolutely no internal electrical charges.

C The internal positive and negative charges exactly balance each other.

D It refuses to dissolve or interact with water molecules.

💡 Short Explanation

�� NH₃⁺ carries a positive charge. �� COO⁻ carries a negative charge. �� Total charge becomes zero.

✅ Correct Answer Explanation

A zwitter ion contains both a positive charge on the ammonium group and a negative charge on the carboxylate group. These charges cancel each other, making the molecule electrically neutral overall.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect explanation.
�� Option B → Charges are present.
�� Option D → Unrelated to neutrality.

🎯 Strategy

Used

Passage-Based Reasoning

Application:

Determine why zwitter ions have no net charge.

Final Logic:

Equal positive and negative charges balance.

🧠 Memory Trick

+1 and –1 = 0

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Zwitter Ionic Structure

15 The biological or laboratory conversion of a dipeptide back into two individual free amino acids requires which type of reaction?

A Condensation

B Hydrolysis

C Hydrogenation

D Oxidation

💡 Short Explanation

�� Peptide bonds are broken by water. �� The reverse of peptide formation is hydrolysis. �� Free amino acids are produced.

✅ Correct Answer Explanation

Hydrolysis breaks peptide bonds through the addition of water, converting a dipeptide into its constituent amino acids.

❓ Why Other Options Are Incorrect

�� Option A → Forms peptide bonds.
�� Option C → Adds hydrogen.
�� Option D → Changes oxidation state.

🎯 Strategy

Used

Reaction Identification

Application:

Determine the reverse process of peptide bond formation.

Final Logic:

Peptide bond cleavage occurs by hydrolysis.

🧠 Memory Trick

Hydrolysis = Break with Water

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Peptide Bond Hydrolysis

16 The arbitrary unit mass distinction between a large polypeptide and a protein is often blurred by nature. Which essential biomolecule acts as a famous exception by being classified natively as a protein despite having only 51 amino acids?

A Myosin

B Keratin

C Insulin

D Albumin

💡 Short Explanation

�� Insulin contains only 51 amino acids. �� It possesses a definite biological function. �� Therefore it is classified as a protein.

✅ Correct Answer Explanation

Although insulin contains fewer amino acids than many typical proteins, it has a well-defined native structure and biological activity, making it a protein.

❓ Why Other Options Are Incorrect

�� Option A → Much larger protein.
�� Option B → Structural protein.
�� Option D → Large plasma protein.

🎯 Strategy

Used

Exception Recall

Application:

Identify the classic exception in protein classification.

Final Logic:

Insulin is a small but functional protein.

🧠 Memory Trick

51 Amino Acids = Insulin

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Proteins and Polypeptides

17 Which set of statements analytically differentiates secondary and tertiary protein structures correctly?

A Secondary structure involves H-bonding between peptide backbone groups; tertiary structure represents the overall 3D folding of the chain.

B Secondary structure determines the sequence of amino acids; tertiary involves multiple sub-units.

C Tertiary structure is stabilised strictly by primary peptide covalent bonds alone.

D Secondary structures always yield complete functional globular shapes directly.

💡 Short Explanation

�� Secondary structure includes α-helices and β-sheets. �� These arise through hydrogen bonding. �� Tertiary structure is the overall three-dimensional folding.

✅ Correct Answer Explanation

Secondary structure results from hydrogen bonding between backbone –C=O and –NH– groups. Tertiary structure refers to the complete three-dimensional folding of a polypeptide chain.

❓ Why Other Options Are Incorrect

�� Option B → Describes primary and quaternary structures.
�� Option C → Tertiary structure involves many interactions.
�� Option D → Secondary structure alone does not create complete globular proteins.

🎯 Strategy

Used

Concept Differentiation

Application:

Compare secondary and tertiary structures.

Final Logic:

Hydrogen bonding → Secondary; Overall folding → Tertiary.

🧠 Memory Trick

Secondary = Helix, Tertiary = Shape

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Protein Structure

18 Match the stabilizing force or structural characteristic with its corresponding protein structural level.

List I	List II
1. — Exact sequence of amino acids	a. — Secondary structure
2. — Hydrogen bonding between –C=O and –NH–	b. — Primary structure
3. — Disulphide linkages, electrostatic and van der Waals forces	c. — Tertiary structure

A 1-b, 2-a, 3-c

B 1-a, 2-b, 3-c

C 1-c, 2-a, 3-b

D 1-b, 2-c, 3-a

💡 Short Explanation

�� Amino acid sequence → Primary. �� Hydrogen bonding → Secondary. �� Multiple interactions → Tertiary.

✅ Correct Answer Explanation

Matching: 1. Exact sequence of amino acids → Primary structure 2. Hydrogen bonding → Secondary structure 3. Disulphide, electrostatic and van der Waals interactions → Tertiary structure Therefore: 1-b, 2-a, 3-c

❓ Why Other Options Are Incorrect

�� The assignments do not correspond to accepted protein structural levels.

🎯 Strategy

Used

Match the Following

Application:

Relate stabilizing forces to structure levels.

Final Logic:

Sequence → Primary, H-bond → Secondary, Multiple interactions → Tertiary.

🧠 Memory Trick

Sequence → Helix → Fold

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Levels of Protein Structure

19 When a complex globular protein (in its tertiary state) denatures due to a severe pH change, what specific bonds or forces are disrupted while the primary sequence remains functionally intact?

A Strong covalent peptide bonds

B Hydrogen bonds, disulphide linkages, and van der Waals forces

C Metallic coordinate bonds

D Alpha-glycosidic linkages

💡 Short Explanation

�� Denaturation disrupts higher-order interactions. �� Peptide bonds remain intact. �� Protein folding is lost.

✅ Correct Answer Explanation

Denaturation affects the forces responsible for secondary and tertiary structures, including hydrogen bonds, disulphide bridges, electrostatic interactions, and van der Waals forces, while the primary sequence remains unchanged.

❓ Why Other Options Are Incorrect

�� Option A → Peptide bonds remain intact.
�� Option C → Not typical stabilizing forces.
�� Option D → Found in carbohydrates.

🎯 Strategy

Used

Concept Application

Application:

Identify forces affected during denaturation.

Final Logic:

Higher-order stabilizing forces are disrupted.

🧠 Memory Trick

Denaturation Breaks Shape, Not Sequence

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Denaturation of Proteins

20 Arrange the structural forces found in native proteins from the strongest (purely covalent backbone) to the weakest typical intermolecular interaction:
A. Primary peptide bond
B. Disulphide linkage (covalent cross-link)
C. van der Waals forces

A 1. A, B, C

B 2. C, B, A

C 3. B, A, C

D 4. A, C, B

💡 Short Explanation

Peptide bonds form the backbone.
Disulphide bonds are strong covalent cross-links.
van der Waals forces are comparatively weak.

✅ Correct Answer Explanation

The decreasing order of strength is:

Primary peptide bond > Disulphide linkage > van der Waals forces

Therefore:

A → B → C

❓ Why Other Options Are Incorrect

They do not follow the accepted order of bond strength.

🎯 Strategy

Ordering

Application:

Compare relative strengths of protein-stabilizing interactions.

Final Logic:

Covalent backbone > Covalent cross-link > Weak intermolecular force.

🧠 Memory Trick

Peptide > Disulphide > van der Waals

📚 Class XII – Chemistry Part II – Chapter: Biomolecules – Topic: Forces Stabilizing Protein Structure

CUET UG Chemistry Booster Test – 3 Structure and Proteins and Amino Acids

CUET UG Chemistry Booster Test - 3 Proteins and Amino Acids

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