Read the case carefully and answer the questions that follow. The $\alpha$-amino acids are the building blocks of proteins. All $\alpha$-amino acids exist as zwitter ion due to which they show amphoteric behaviour. All amino acids are joined through peptide bond. Proteins are broadly classified as globular proteins and fibrous proteins. Globular proteins are water soluble, whereas fibrous proteins are not. The complete structure of protein is discussed at four different levels i.e. primary, secondary, tertiary and quaternary structures. Protein loses its biological activity in denatured form. (a) Define the following : (i) Peptide linkage (ii) Denatured protein (b) Why do amino acids show amphoteric behaviour ? (c) (i) How can you differentiate between Fibrous protein and Globular protein ? OR (c) (ii) Write the names of two different secondary structures of proteins.

Read the case carefully and answer the questions that follow. The α-amino acids are the building blocks of pro

Question

\alpha

(a) Define the following :

(i) Peptide linkage

(ii) Denatured protein

(b) Why do amino acids show amphoteric behaviour ?

(c)

(i) How can you differentiate between Fibrous protein and Globular protein ?

(OR)

(c)

(ii) Write the names of two different secondary structures of proteins.

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Part (a)Concept understanding — Biochemical Bonds

Biochemical Bonds: The Glue That Holds Life Together

Imagine you're building with LEGO bricks. Some bricks click together tightly and never come apart unless you really yank them. Others snap together lightly and can be pulled apart with a gentle tug. Some bricks don't even click — they just stick because of static cling or magnetism.

Biochemical bonds are exactly like that. They are the forces that hold atoms together inside the molecules of your body — your DNA, proteins, fats, and carbohydrates. Without these bonds, you'd literally fall apart into a pile of individual atoms.

The Core Idea

Atoms bond because being bonded is more stable (lower energy) than being alone. Think of it like this: a single atom is like a person standing alone in a cold room. Bonding is like huddling together for warmth — you lose some freedom of movement, but you gain stability.

In biochemistry, we care about four main types of bonds. They differ in strength, how they form, and what they do in living systems.

1. Covalent Bonds — The Strong, Permanent LEGO Clicks

This is the strongest bond in biology. Two atoms share electrons — like two people holding the same umbrella. Each atom contributes one or more electrons, and they both "own" the pair.

Key properties:

Very strong (100–400 kJ/mol)
Forms the backbone of all biomolecules
Takes a lot of energy (or enzymes) to break

Where you find it:

The carbon-carbon bonds in your DNA's sugar-phosphate backbone
The peptide bonds linking amino acids into proteins
The bonds within a glucose molecule

Note

A single covalent bond shares 2 electrons. A double bond shares 4. Triple bonds are rare in biology but exist (e.g., in cyanide).

2. Ionic Bonds — The Static Cling of Opposites

Some atoms steal electrons from others. When that happens, one atom becomes positively charged (lost an electron) and the other becomes negatively charged (gained one). Opposite charges attract — that's an ionic bond.

Key properties:

Moderate strength (5–100 kJ/mol in dry conditions)
Very weak in water (because water molecules get in between)
Easily broken by changes in pH or salt concentration

Where you find it:

In salt bridges that help proteins fold into their correct shape
Between the phosphate groups of DNA and positively charged proteins (histones)

Watch out

Ionic bonds are often called "bonds" but in water they behave more like attractions. Don't confuse them with covalent bonds — they're much weaker in biological fluids.

3. Hydrogen Bonds — The Gentle, Reversible Magnets

This is the most important weak bond in biology. A hydrogen atom that's already covalently bonded to an electronegative atom (like oxygen or nitrogen) gets a slight positive charge. It then gets attracted to another electronegative atom nearby.

Think of it like a weak magnet — it holds things together but can be easily undone.

Key properties:

Weak individually (5–30 kJ/mol)
But many together can be very strong
Easily broken by heat or changes in pH
Directional — they only work when atoms are properly aligned

Where you find it:

Between the two strands of DNA (this is what holds the double helix together)
In protein folding (between amino acids in the backbone)
Between water molecules (giving water its unique properties)

Important

Hydrogen bonds are the reason DNA can unzip for replication. If DNA used covalent bonds between strands, it would be impossible to separate without destroying the molecule.

4. Van der Waals Interactions — The Fleeting, Accidental Touches

Even neutral atoms have temporary, uneven distributions of electrons. These create tiny, momentary charges that attract nearby atoms. It's like two people accidentally brushing shoulders in a crowd — brief, weak, but real.

Key properties:

Extremely weak (0.5–5 kJ/mol per interaction)
Only work when atoms are very close (within 0.3–0.4 nm)
Add up significantly when many atoms are packed together

Where you find it:

In the hydrophobic core of proteins (where oily amino acids pack tightly)
Between lipid tails in cell membranes
In enzyme-substrate binding (helps "grip" the substrate)

Putting It All Together: A Biological Example

Consider a protein in your body. It's a long chain of amino acids held together by covalent peptide bonds. That chain then folds into a specific shape. The folding is guided by:

Hydrogen bonds between backbone atoms (forming alpha helices and beta sheets)
Ionic bonds between charged side chains …

Why this formula?

Biochemical Bonds: Why the Key Formulas Hold

Biochemical bonds are the forces that hold atoms together in biomolecules. The key formulas come from electrostatics and quantum mechanics — not from biology itself. Let's break down the why behind the most important ones.

1. Ionic Bond Energy: Coulomb's Law

Formula:

E = \frac{k \cdot q_1 \cdot q_2}{r}

Why it holds:

Opposite charges attract — this is a fundamental law of physics (Coulomb's law).
In a biochemical context, consider a sodium ion ( $\text{Na}^+$ ) and a chloride ion ( $\text{Cl}^-$ ). The energy released when they come together is directly proportional to the product of their charges ( $q_1 q_2$ ) and inversely proportional to the distance ( $r$ ) between them.
The constant $k$ accounts for the medium (water vs. vacuum). In water, the effective force is weaker because water molecules partially shield the charges — this is why ionic bonds in biology are often weaker in aqueous environments.

Key insight: The formula is not arbitrary — it's derived from the inverse-square law of electrostatics, integrated over the distance the charges move toward each other.

2. Covalent Bond Energy: The Morse Potential (Approximation)

Formula (simplified):

E = D_e \left(1 - e^{-a(r - r_0)}\right)^2

Why it holds:

Covalent bonds arise from shared electrons between atoms. The energy is not a simple inverse-square law because electrons are delocalized.
The Morse potential is an empirical formula that captures two key observations:
1. At equilibrium distance ( $r_0$ ): Energy is minimum ( $E = 0$ in this form).
2. If atoms are pulled apart ( $r \to \infty$ ): Energy approaches $D_e$ (the bond dissociation energy).
3. If atoms are pushed too close ( $r \to 0$ ): Energy skyrockets due to Pauli repulsion (electrons can't occupy the same space).
The exponential term $e^{-a(r - r_0)}$ models the rapid drop in attractive force as distance increases — this comes from quantum mechanical overlap of electron clouds.

Key insight: The formula is a curve fit to quantum mechanical calculations, not a first-principles derivation. But it works because it respects the physics: attraction at long range, repulsion at short range, and a stable minimum.

3. Hydrogen Bond Energy: Dipole-Dipole Interaction

Formula (approximate):

E \approx -\frac{2 \mu_1 \mu_2}{4 \pi \epsilon_0 r^3} \cdot \cos\theta

Why it holds:

A hydrogen bond (e.g., between water molecules) is not a true bond — it's a strong dipole-dipole interaction.
The dipole moment ( $\mu$ ) arises because oxygen is more electronegative than hydrogen, creating partial charges ( $\delta^+$ and $\delta^-$ ).
The energy depends on:
- Strength of dipoles ( $\mu_1 \mu_2$ )
- Distance ( $r$ ) — falls off as $1/r^3$ , much faster than ionic bonds ( $1/r$ )
- Orientation ( $\cos\theta$ ) — strongest when dipoles are aligned head-to-tail

Key insight: The $1/r^3$ dependence comes from the derivative of the dipole field. Unlike point charges, dipoles have a field that decays faster — this is why hydrogen bonds are directional and weaker than covalent bonds.

4. Van der Waals Interaction: Lennard-Jones Potential

Formula:

E = 4\epsilon \left[ \left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^6 \right]

Why it holds:

Van der Waals forces arise from temporary fluctuations in electron distribution — even nonpolar molecules have instantaneous dipoles. …

Part (b)Concept understanding — Protein Structure Levels

Protein Structure Levels: From a String to a Working Machine

Imagine you have a long string of beads. Each bead is a different colour, and the order of colours is fixed. If you just lay that string on a table, it's a floppy, useless line. But if you could somehow make that string fold itself into a tiny, precise 3D shape — say, a key that fits a specific lock — you'd have something that actually does a job. That's exactly what a protein is.

A protein starts as a long chain of smaller units called amino acids. There are 20 different kinds, each with a unique side chain (the "colour" of the bead). The exact sequence of these amino acids is determined by your DNA. But a protein isn't just a chain — it's a chain that folds into a specific shape, and that shape determines what the protein does. If the shape is wrong, the protein can't work.

The folding happens in stages, and we call these stages the four levels of protein structure.

Level 1: Primary Structure — The Sequence

This is the simplest level: just the linear order of amino acids in the chain, linked by peptide bonds. Think of it as the sentence written in the language of proteins.

Primary structure = the sequence of amino acids from the N-terminus (start) to the C-terminus (end).

Why does this matter? Because the sequence determines everything else. Change one amino acid in a critical spot, and the entire protein can misfold. Example: sickle cell anaemia is caused by a single amino acid swap in haemoglobin — valine replaces glutamic acid at position 6. One bead out of hundreds changes colour, and the whole protein folds wrong.

Level 2: Secondary Structure — Local Folding Patterns

The chain doesn't stay straight. Hydrogen bonds form between the backbone atoms (not the side chains) of nearby amino acids. These bonds cause the chain to twist or fold into regular, repeating patterns.

Two common patterns:

Alpha helix ( $\alpha$ -helix): The chain coils like a spring or a spiral staircase. Hydrogen bonds form between every 4th amino acid, holding the coil tight.
Beta sheet ( $\beta$ -sheet): The chain folds back and forth like a pleated fan. Hydrogen bonds form between adjacent segments, creating a flat, sheet-like structure.

Note

Secondary structure is stabilised entirely by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another — both part of the peptide backbone. Side chains stick out and don't participate.

These patterns are local — they happen in short stretches of the chain. A single protein can have multiple $\alpha$ -helices and $\beta$ -sheets separated by loops.

Level 3: Tertiary Structure — The Global 3D Shape

Now the whole chain folds into its final, compact, three-dimensional shape. This is where the protein becomes functional. The tertiary structure is stabilised by interactions between the side chains of amino acids that may be far apart in the sequence but come close in space.

What holds it together?

Hydrophobic interactions: Nonpolar side chains cluster together in the protein's interior, away from water.
Hydrogen bonds: Between polar side chains.
Ionic bonds: Between positively and negatively charged side chains.
Disulfide bridges: Covalent bonds between the sulfur atoms of two cysteine amino acids — these are strong and lock parts of the chain together.
Van der Waals forces: Weak attractions between closely packed atoms.

Watch out

A common mistake: thinking tertiary structure is just "more secondary structure." It's not. Secondary structure is local folding; tertiary structure is the global arrangement of the entire chain, including how helices and sheets pack together.

Level 4: Quaternary Structure — Multiple Chains Working Together

Some proteins are made of more than one polypeptide chain. Each chain is a separate subunit, and the quaternary structure describes how these subunits assemble into a functional complex. …

Why this formula?

Protein Structure Levels: Understanding the "Why" Behind the Hierarchy

Protein structure is not defined by a single formula, but by a logical hierarchy of organization. Each level builds on the previous one, and the "formulas" here are really principles of molecular interaction that explain why proteins fold the way they do.

Let's break down each level and the reasoning behind its key features.

1. Primary Structure: The Sequence "Formula"

What it is: The linear sequence of amino acids linked by peptide bonds.

Key "formula":

\text{Protein} = \text{NH}_2\text{-[Amino Acid]}_1\text{-[AA]}_2\text{-...-[AA]}_n\text{-COOH}

Why this holds:

Peptide bond formation is a condensation reaction:

\text{-COOH} + \text{NH}_2\text{-} \rightarrow \text{-CO-NH-} + \text{H}_2\text{O}

This bond is rigid and planar due to resonance (partial double-bond character). This restricts rotation, which directly influences higher-order folding.
The sequence is determined by DNA (genetic code). Every change in sequence can alter the entire structure — this is why a single mutation (e.g., sickle cell anemia: Glu → Val at position 6) can cause disease.

Exam insight: The primary structure is the only level that is covalently determined. All higher levels are non-covalent interactions.

2. Secondary Structure: Local Folding Patterns

Key patterns: $\alpha$ -helix and $\beta$ -pleated sheet.

Why these form — the hydrogen bond "formula":

The $\alpha$ -helix

Hydrogen bonds form between the carbonyl oxygen ( $\text{C=O}$ ) of residue $n$ and the amide hydrogen ( $\text{N-H}$ ) of residue $n+4$ .
Why $n+4$ ? This spacing allows the backbone to coil into a right-handed helix with exactly 3.6 amino acids per turn.
Reasoning: The peptide bond's planar nature forces the backbone into a specific geometry. The $n+4$ pattern maximizes H-bonding while minimizing steric clashes.

The $\beta$ -sheet

Hydrogen bonds form between adjacent strands (either parallel or antiparallel).
Why not $n+4$ ? The backbone is extended (pleated), so H-bonds occur between different segments, not within the same chain.

Key formula (Ramachandran plot):

Only certain backbone dihedral angles ( $\phi, \psi$ ) are allowed:

$\alpha$ -helix: $\phi \approx -57^\circ$ , $\psi \approx -47^\circ$
$\beta$ -sheet: $\phi \approx -130^\circ$ , $\psi \approx +130^\circ$

Why these angles? Steric hindrance — atoms cannot overlap. The Ramachandran plot shows the only regions where no two atoms clash.

3. Tertiary Structure: The 3D Fold

Key "formula": The hydrophobic effect drives folding.

Why this holds:

Water molecules form a cage-like structure around nonpolar (hydrophobic) side chains. This is entropically unfavorable (water loses freedom).
To minimize this, hydrophobic side chains cluster together in the protein's core, away from water.
Result: The protein collapses into a compact globule, with polar/charged residues on the surface.

Supporting interactions (the "glue"):

Interaction	Why it matters
Hydrogen bonds	Between side chains (e.g., Ser–Glu)
Ionic bonds	Between charged groups (e.g., Lys–Asp)
Van der Waals forces	Close packing of atoms
Disulfide bridges	Covalent S–S bonds (only in oxidizing environments)

Why not just one formula? Tertiary structure is unique to each protein — it's the sum of all these interactions, not a single equation.

4. Quaternary Structure: Multiple Subunits

Key "formula":

\text{Functional protein} = \sum_{i=1}^{n} \text{Subunit}_i

Why this holds:

Some proteins need multiple polypeptide chains to function (e.g., hemoglobin: $\alpha_2\beta_2$ ). …

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Part (a)

(a) Definitions

(i) Peptide linkage: the amide bond –CO–NH– formed when the –COOH of one amino acid condenses with the –NH $_2$ of another, with loss of a water molecule; it links amino acids into a polypeptide chain.
(ii) Denatured protein: a protein that has lost its native secondary/tertiary/quaternary structure (by heat, pH change or chemicals) and hence its biological activity, while its primary structure (sequence) remains intact.

(b) Amphoteric behaviour. An α‑amino acid has both an acidic –COOH and a basic –NH $_2$ group and exists as a zwitterion $\text{H}_3\overset{+}{\text{N}}\text{-CHR-COO}^-$ . In acid it accepts H $^+$ (behaves as a base); in base it donates H $^+$ (behaves as an acid) — so it reacts with both acids and bases.

(c)(i) Fibrous vs globular protein

Fibrous	Globular
long, thread‑like; water‑insoluble	spherical, compact; water‑soluble

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Part (a): peptide linkage = –CO–NH– amide bond; denatured protein = protein that has lost its 3‑D shape and activity (sequence intact); amino acids are amphoteric via their zwitterion; fibrous = insoluble/structural, globular = soluble/functional. Part (c): the two secondary structures are the α‑helix and β‑pleated sheet.

Part (a)

(a)(i) Peptide linkage. When the –COOH of one amino acid reacts with the –NH $_2$ of another, water is eliminated and an amide –CO–NH– bond forms:

\text{R-CH(NH}_2)\text{-COOH} + \text{H}_2\text{N-CH(R')-COOH} \rightarrow \text{R-CH(NH}_2)\text{-CO-NH-CH(R')-COOH} + \text{H}_2\text{O}

This peptide bond has partial double‑bond character (restricted rotation), giving the protein backbone its defined geometry.

(a)(ii) Denatured protein. External stress (heat, extreme pH, chemicals) breaks the H‑bonds, ionic and hydrophobic interactions that hold the folded shape, so the protein unfolds and loses biological activity. The peptide bonds (primary sequence) are not broken. Example: egg‑white coagulating on heating.

(b) Why amino acids are amphoteric. Each α‑amino acid carries an acidic –COOH and a basic –NH $_2$ on the same carbon; internally the –COOH proton transfers to –NH $_2$ to give the dipolar zwitterion:

\text{H}_2\text{N-CHR-COOH} \rightleftharpoons \text{H}_3\overset{+}{\text{N}}\text{-CHR-COO}^-

In acidic solution the –COO $^-$ picks up H $^+$ → cation (acts as a base).
In basic solution the –NH $_3^+$ loses H $^+$ → anion (acts as an acid).

Reacting with both acids and bases = amphoteric behaviour (the pH of zero net charge is the isoelectric point, pI).

(c)(i) Fibrous vs globular proteins.

Property	Fibrous	Globular
Shape	long, thread‑like strands	compact, spherical
Solubility	insoluble in water	soluble in water
Function	structural/protective	catalytic/transport/regulatory

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

Showing the 12 most recent of 47 on this concept.

CBSE 2026Set 56/2/11 markMCQ
$\alpha$
›Reveal solutionSolution
Proteins are linear chains of $\alpha$ -amino acids linked by peptide bonds — a specific type of covalent bond formed between the carboxyl group of one amino acid and the amino group of the next, with the elimination of water. The correct answer is (B) Peptide Bond.

Why This Question Tests a Core Biochemical Idea

The question is about the primary structure of proteins — the simplest level of protein organization. A protein is a polymer, and like any polymer, it has repeating units (monomers) held together by a specific chemical linkage. The monomers here are $\alpha$ -amino acids, and the linkage that joins them is not just any covalent bond — it has a special name because of how it forms and its unique properties.

Many students get confused because all the options are types of bonds found in biomolecules. The trick is to match the bond to the specific monomers and the reaction that creates it.

Step-by-Step Reasoning

Identify the monomers. Proteins are built from $\alpha$ -amino acids. Each amino acid has a central carbon ( $\alpha$ -carbon) bonded to an amino group ( $-\mathrm{NH}_2$ ), a carboxyl group ( $-\mathrm{COOH}$ ), a hydrogen atom, and a variable side chain ( $R$ ). The key functional groups for linking are the $-\mathrm{NH}_2$ and $-\mathrm{COOH}$ groups.

Understand how two amino acids join. When two amino acids link, the carboxyl group of the first amino acid reacts with the amino group of the second. This is a condensation reaction (also called dehydration synthesis) — a molecule of water ( $\mathrm{H}_2\mathrm{O}$ ) is removed. The oxygen from the carboxyl group and two hydrogens from the amino group form the water.

Name the resulting bond. The chemical bond that forms between the carbon of the first amino acid's carboxyl group and the nitrogen of the second amino acid's amino group is called an amide bond. In biochemistry, this specific amide bond between amino acids is universally known as a peptide bond. The structure is $-\mathrm{CO}-\mathrm{NH}-$ .

Eliminate the other options.

(A) Covalent Bond — This is too broad. A peptide bond is a covalent bond, but the question asks for the specific name of the bond joining amino acids in proteins. "Covalent bond" is the general category, not the precise answer.

(C) Glycosidic Bond — This bond joins monosaccharides to form carbohydrates (e.g., starch, cellulose). It involves a sugar's anomeric carbon and an alcohol or another sugar. It has nothing to do with amino acids.

(D) Coordinate Bond — This is a special type of covalent bond where both shared electrons come from the same atom. It is found in coordination complexes (e.g., metal ions with ligands) and is not the standard linkage in protein backbones. …
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CBSE 2026Set ANNUAL1 markMCQ
$Q. An example of fibrous protein is$
(a) Keratin
(b) Myosin
(c) Both (A) and (B)
(d) None of these
›Reveal solutionSolution
Fibrous proteins have elongated, thread-like molecules that lie parallel in bundles held by hydrogen and disulfide bonds; keratin and myosin are both classic examples.

Fibrous proteins are structural proteins with molecules arranged as long fibres or sheets:

Keratin: found in hair, nails, wool, horn - a structural/protective fibrous protein. …
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CBSE 2026Set ANNUAL1 markMCQ
$Q. alpha-helix structure is found in$
(a) DNA
(b) RNA
(c) Lipid
(d) Protein
›Reveal solutionSolution

The alpha-helix is one of the two common secondary structures of proteins, stabilised by intramolecular hydrogen bonds between backbone N-H and C=O groups.

In the alpha-helix, the polypeptide chain coils into a right-handed spiral, held in shape by hydrogen bonds formed between the C=O of one amino acid residue and the N-H of another residue further along the same chain (typically four residues away). This is a form of secondary protein structure (alongside the beta-pleated sheet).

…

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CBSE 2026Set ANNUAL1 mark
$Q. Fill in the blank: Only ______ are obtained on hydrolysis of Protein.$
›Reveal solutionSolution

Hydrolysis of protein gives only alpha-amino acids.

Proteins are polymers of alpha-amino acids joined by peptide (amide) linkages. On complete hydrolysis (acid, base or enzyme catalysed), every peptide bond is cleaved and the protein is broken down completely in …

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CBSE 2026Set ANNUAL1 mark
$Q. What is the difference in the linkages between α-helix and β-pleated structures of proteins?$
›Reveal solutionSolution
α-helix = hydrogen bonds within the same chain (intramolecular); β-pleated sheet = hydrogen bonds between adjacent chains (intermolecular).

The secondary structure of a protein describes how the polypeptide backbone coils or folds, and it is stabilised by hydrogen bonds between the $>C=O$ and $>N-H$ groups of the peptide bonds.

α-Helix: the polypeptide chain twists into a right-handed spiral. Each $>C=O$ group forms a hydrogen bond with the $>N-H$ group of the fourth amino-acid residue within the same chain. These hydrogen bonds are therefore intramolecular. …
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CBSE 2025Set A1 mark
$Q. Fill in the blank: If third amino acid combines to a dipeptide, the product is called a ______.$
›Reveal solutionSolution

A peptide is named by how many amino acid residues it contains: two = dipeptide, three = tripeptide, and so on.

When two amino acids join through a peptide (amide) bond, formed by condensation between the –COOH of one amino acid and the –NH2 of another (with loss of a water molecule), the product is a dipeptide. If a third amino acid molecule now condenses onto this dipeptide (forming another peptide bond), the r …

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CBSE 2025Set ANNUAL1 mark
$Q. Write two examples of fibrous proteins.$
›Reveal solutionSolution
Fibrous proteins are elongated, thread-like protein molecules held together by hydrogen and disulphide bonds, forming fibres; keratin and collagen are classic examples.

Fibrous proteins have molecules arranged as parallel polypeptide chains held together by hydrogen and disulphide bonds, forming long fibre-like or thread-like structures. They are typically insoluble in water and provide structural/mechanical support.

Examples:

Keratin - found in hair, wool, nails, horns, feathers. …
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CBSE 2025Set ANNUAL1 mark
$Q. Proteins are polymers of what?$
›Reveal solutionSolution

Proteins are polypeptides - long chains built from alpha-amino acid monomer units joined by peptide bonds.

Proteins are biopolymers made of many alpha-amino acid units linked together through peptide bonds (an amide linkage, -CO-NH-, formed between the -COOH group of one amino acid and the -NH2 group of the next, with loss of water). The specific sequence of …

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CBSE 2024Set D1 markMCQ
$Q. The helical structure of protein is stabilized by which of the following?$
(a) Ionic bond
(b) Covalent bond
(c) van der Waals forces
(d) Hydrogen bond
›Reveal solutionSolution

Protein helix is held together by hydrogen bonds (secondary structure).

The secondary structure of proteins (the alpha-helix and beta-pleated sheet) is stabilized by HYDROGEN BONDING between the carbonyl oxygen (>C=O) of one peptide bond and the amide hydrogen (>N-H) of another. In the alpha-helix these H-bonds run roughly par …

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CBSE 2024Set B1 mark
$Q. Write True or False: Keratin is a globular proteins.$
›Reveal solutionSolution

Proteins are classified as fibrous or globular based on shape; keratin (found in hair, nails, wool) is fibrous, not globular.

Fibrous proteins have long thread-like/elongated molecules that lie side by side to form fibres, held together by hydrogen and disulphide bonds — examples include keratin (hair, nails, wool) and myosin (muscles). Globular proteins, by contrast, have their polypeptide chains coiled around themselves into a roughly sph …

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CBSE 2024Set B1 mark
$Q. Match the pairs correctly. Column A item: 'Protein'. Column B options:$
(a) C6H5SO2Cl
(b) Keratin
(c) C6H5NH2
(d) Rickets
(e) C6H5N2Cl
(f) Cobalt. Which option from Column B matches 'Protein'?
›Reveal solutionSolution

Keratin, found in hair/nails/wool, is a structural protein, so it is the example that pairs with 'Protein' in this list.

Of the options given, C6H5SO2Cl, C6H5NH2 and C6H5N2Cl are simple aromatic organic compounds (a sulphonyl chloride, aniline, and a diazonium salt respectively), Rickets is a disease, and …

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CBSE 2024Set ANNUAL1 markMCQ
$Q. Globular protein is -$
(a) Insulin
(b) Keratin
(c) Myosin
(d) Collagen
›Reveal solutionSolution

Proteins are classified by shape into fibrous (elongated, thread-like, structural) and globular (coiled, compact, functional); insulin belongs to the globular class.

Fibrous proteins have polypeptide chains that run parallel in long fibres/sheets held by hydrogen and disulphide bonds - examples include keratin (hair, nails), myosin (muscle), and collagen (connective tissue/tendons); they are typically insoluble in water and play structural roles. …

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Part (a)

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