NCERT Solutions for Class 11 Biology Chapter 9: Biomolecules
Complete NCERT Class 11 Biology Chapter 9 solutions: chemical composition of living tissues, primary and secondary metabolites, biomacromolecules, proteins, polysaccharides, nucleic acids, protein structure and enzymes — all 11 exercises answered with Figures 9.1–9.5.
Chapter at a glance — complete revision notes
Introduction — are all living organisms made of the same chemicals?
- Living organisms show wide diversity, yet an elemental analysis of a plant tissue, animal tissue or microbial paste gives a list of elements (carbon, hydrogen, oxygen and several others) with their content per unit mass of the tissue.
- The same analysis on a piece of earth’s crust (non-living matter) gives a similar list — in absolute terms no element is unique to living tissue; every element of the crust is also present in a living sample.
- The difference lies in relative abundance: carbon and hydrogen are far higher in living organisms than in the earth’s crust (Table 9.1).
Table 9.1 — A comparison of elements present in non-living and living matter (% weight; adapted from CNR Rao, Understanding Chemistry)
| Element | Earth’s crust (% weight) | Human body (% weight) |
|---|---|---|
| Hydrogen (H) | 0.14 | 9.5 |
| Carbon (C) | 0.03 | 18.5 |
| Oxygen (O) | 46.6 | 65.0 |
| Nitrogen (N) | very little | 3.3 |
| Sulphur (S) | 0.03 | 0.3 |
| Sodium (Na) | 2.8 | 0.2 |
| Calcium (Ca) | 3.6 | 1.5 |
| Magnesium (Mg) | 2.1 | 0.1 |
| Silicon (Si) | 27.7 | negligible |
- Reading the table: C, H, N and S are much richer in the human body; Si, Na, Ca and Mg are richer (or only present) in the crust — so life is built on carbon chemistry, not on silicate chemistry.
9.1 How to analyse chemical composition?
- Step 1 — grind a living tissue (a vegetable or a piece of liver) in trichloroacetic acid (Cl3CCOOH) in a mortar and pestle → a thick slurry.
- Step 2 — strain through cheesecloth or cotton → two fractions: the filtrate (the acid-soluble pool) and the retentate (the acid-insoluble fraction). Thousands of organic compounds are found in the acid-soluble pool.
- Isolation and purification: the compounds are extracted, then the extract is subjected to separation techniques until one compound is separated from all others; analytical techniques then give its molecular formula and probable structure.
- All carbon compounds obtained from living tissues are called biomolecules.
- Inorganic constituents: weigh a small amount of tissue (wet weight), dry it (water evaporates → dry weight), then burn it completely — carbon compounds are oxidised to CO2 and water vapour and the remaining ash contains inorganic elements (calcium, magnesium etc.). Inorganic compounds such as sulphate and phosphate are also seen in the acid-soluble fraction.
- So elemental analysis gives the elemental composition (H, O, Cl, C etc.) while analysis for compounds gives the kind of organic (Figure 9.1) and inorganic constituents (Table 9.2).
- From a chemistry point of view one identifies functional groups (aldehydes, ketones, aromatic compounds); from a biological point of view the compounds are classed as amino acids, nucleotide bases, fatty acids etc.
Table 9.2 — Representative inorganic constituents of living tissues
| Component | Formula |
|---|---|
| Sodium | Na+ |
| Potassium | K+ |
| Calcium | Ca++ |
| Magnesium | Mg++ |
| Water | H2O |
| Compounds | NaCl, CaCO3, PO43−, SO42− |
Organic compounds of Figure 9.1 — amino acids, lipids, nucleotides
Amino acids
- Organic compounds with an amino group and an acidic (carboxyl) group on the same carbon — the α-carbon; hence α-amino acids. They are substituted methanes.
- Four valencies of the α-carbon are occupied by hydrogen, carboxyl group, amino group and a variable R group.
- Only twenty R-group types occur in proteins (proteinaceous amino acids): R = H → glycine; R = methyl → alanine; R = hydroxy methyl → serine (three of the twenty are in Figure 9.1).
- Based on the number of amino and carboxyl groups: acidic (glutamic acid), basic (lysine), neutral (valine). Aromatic amino acids: tyrosine, phenylalanine, tryptophan.
- Property: the ionizable nature of –NH2 and –COOH groups, so the structure of an amino acid changes in solutions of different pH; the form B (in NCERT’s equation) is the zwitterionic form.
Lipids
- Generally water insoluble. A fatty acid has a carboxyl group attached to an R group (methyl –CH3, ethyl –C2H5 or 1 to 19 –CH2 groups). Palmitic acid has 16 carbons including the carboxyl carbon; arachidonic acid has 20.
- Fatty acids may be saturated (no double bond) or unsaturated (one or more C=C).
- Glycerol is trihydroxy propane. Many lipids have both glycerol and fatty acids esterified → mono-, di- and triglycerides, also called fats and oils on the basis of melting point (oils have lower melting point, e.g., gingelly oil, so remain as oil in winter).
- Phospholipids contain phosphorus and a phosphorylated organic compound; they are found in cell membranes (example: lecithin). Neural tissues have lipids with still more complex structures.
Nitrogen bases, nucleosides and nucleotides
- Heterocyclic-ring compounds: nitrogen bases adenine, guanine, cytosine, uracil, thymine.
- Base + sugar = nucleoside (adenosine, guanosine, thymidine, uridine, cytidine). Base + sugar + phosphate esterified to the sugar = nucleotide (adenylic acid, thymidylic acid, guanylic acid, uridylic acid, cytidylic acid).
- Nucleic acids (DNA, RNA) consist of nucleotides only and function as the genetic material.
- Figure 9.1 also shows sugars — glucose C6H12O6 and ribose C5H10O5 — and the bases adenine (a purine) and uracil (a pyrimidine).
9.2 Primary and secondary metabolites
- The thousands of biomolecules (amino acids, sugars etc.) are also called metabolites. In animal tissues all categories shown in Figure 9.1 are present — these are primary metabolites.
- Plant, fungal and microbial cells contain thousands of compounds other than these — alkaloids, flavonoids, rubber, essential oils, antibiotics, coloured pigments, scents, gums, spices — the secondary metabolites (Table 9.3).
- Primary metabolites have identifiable functions and known roles in normal physiological processes; the role of many secondary metabolites in the host organism is not yet understood, but many are useful to human welfare (rubber, drugs, spices, scents, pigments) and some have ecological importance.
Table 9.3 — Some secondary metabolites
| Class | Examples |
|---|---|
| Pigments | Carotenoids, anthocyanins, etc. |
| Alkaloids | Morphine, codeine, etc. |
| Terpenoids | Monoterpenes, diterpenes etc. |
| Essential oils | Lemon grass oil, etc. |
| Toxins | Abrin, ricin |
| Lectins | Concanavalin A |
| Drugs | Vinblastin, curcumin, etc. |
| Polymeric substances | Rubber, gums, cellulose |
9.3 Biomacromolecules
- All compounds of the acid-soluble pool have molecular weights from about 18 to around 800 daltons (Da).
- The acid-insoluble fraction has only four types of organic compounds — proteins, nucleic acids, polysaccharides and lipids. Except lipids, these have molecular weights of the order of ten thousand daltons and above.
- So biomolecules are of two types: micromolecules (simply ‘biomolecules’; molecular weight less than 1000 Da) and macromolecules / biomacromolecules (acid-insoluble fraction).
- Why do lipids (MW < 800 Da) come in the macromolecular fraction? Lipids are present not only as such but also arranged into cell membrane and other membranes. Grinding disrupts the cell structure; membranes break into pieces and form vesicles which are not water soluble, so they separate with the acid-insoluble pool. Therefore lipids are not strictly macromolecules.
- The acid-soluble pool represents roughly the cytoplasmic composition; the macromolecules of cytoplasm and organelles become the acid-insoluble fraction — together they represent the entire chemical composition of a tissue or organism.
- Water is the most abundant chemical in living organisms (Table 9.4).
Table 9.4 — Average composition of cells
| Component | % of the total cellular mass |
|---|---|
| Water | 70–90 |
| Proteins | 10–15 |
| Carbohydrates | 3 |
| Lipids | 2 |
| Nucleic acids | 5–7 |
| Ions | 1 |
9.4 Proteins
- Proteins are polypeptides — linear chains of amino acids linked by peptide bonds (Figure 9.3).
- Each protein is a polymer of amino acids; as there are 20 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine), a protein is a heteropolymer and not a homopolymer (a homopolymer has only one type of monomer repeating ‘n’ times).
- Amino acids can be essential (must be supplied through the diet) or non-essential (the body can make them); dietary proteins are the source of essential amino acids.
- Functions: some proteins transport nutrients across the cell membrane, some fight infectious organisms, some are hormones, some are enzymes (Table 9.5).
- Collagen is the most abundant protein in the animal world and RuBisCO (Ribulose bisphosphate Carboxylase-Oxygenase) is the most abundant protein in the whole biosphere.
Table 9.5 — Some proteins and their functions
| Protein | Function |
|---|---|
| Collagen | Intercellular ground substance |
| Trypsin | Enzyme |
| Insulin | Hormone |
| Antibody | Fights infectious agents |
| Receptor | Sensory reception (smell, taste, hormone, etc.) |
| GLUT-4 | Enables glucose transport into cells |
9.5 Polysaccharides
- Polysaccharides (carbohydrates) are another class of macromolecules in the acid-insoluble pellet — long chains of sugars, literally ‘threads’ with monosaccharides as building blocks.
- Cellulose is a polymer of only one monosaccharide, glucose — a homopolymer. Starch is a variant, present as the store house of energy in plant tissues; animals have another variant, glycogen. Inulin is a polymer of fructose.
- In a polysaccharide chain (say glycogen) the right end is the reducing end and the left end is the non-reducing end; the chain has branches (Figure 9.2).
- Starch forms helical secondary structures and can hold I2 molecules in the helix — the starch–I2 complex is blue. Cellulose does not contain complex helices and hence cannot hold I2.
- Plant cell walls are made of cellulose; paper from plant pulp and cotton fibre is cellulosic.
- More complex polysaccharides have amino-sugars and chemically modified sugars (glucosamine, N-acetyl galactosamine) as building blocks; chitin in the exoskeletons of arthropods is such a polysaccharide (mostly homopolymers).
9.6 Nucleic acids
- The other macromolecule of the acid-insoluble fraction; polynucleotides. Together with polysaccharides and polypeptides they form the true macromolecular fraction of a living tissue.
- Building block = nucleotide with three chemically distinct components: a heterocyclic compound, a monosaccharide and phosphoric acid (phosphate).
- Heterocyclic compounds = nitrogenous bases adenine, guanine, uracil, cytosine, thymine. Adenine and guanine are substituted purines; the rest are substituted pyrimidines (the skeletal heterocyclic rings are called purine and pyrimidine).
- Sugar = ribose (pentose monosaccharide) or 2′-deoxyribose. A nucleic acid containing deoxyribose = DNA; containing ribose = RNA.
| Feature | DNA | RNA |
|---|---|---|
| Sugar | 2′-deoxyribose | Ribose |
| Nitrogenous bases | Adenine, guanine, cytosine, thymine | Adenine, guanine, cytosine, uracil |
| Component of a nucleotide | Base + deoxyribose + phosphate | Base + ribose + phosphate |
| Function (NCERT) | Genetic material | Genetic material (nucleic acids serve as genetic material) |
9.7 Structure of proteins
- Structure means different things in different contexts: in inorganic chemistry it is the molecular formula (NaCl, MgCl2); organic chemists write a two-dimensional view (benzene, naphthalene); physicists conjure up the three-dimensional view; biologists describe protein structure at four levels.
- Primary structure (Fig. 9.3a): the sequence of amino acids — the positional information (first, second …). The protein is imagined as a line: left end = N-terminal (first) amino acid, right end = C-terminal (last) amino acid.
- Secondary structure (Fig. 9.3b): the thread is not an extended rigid rod; some portions are folded as a helix (like a revolving staircase) — only right-handed helices are observed in proteins; other regions are folded into other forms (e.g., the β-pleated sheet).
- Tertiary structure (Fig. 9.3c): the long chain is folded upon itself like a hollow woolen ball, giving a 3-dimensional view; it is absolutely necessary for the many biological activities of proteins.
- Quaternary structure (Fig. 9.3d): some proteins are an assembly of more than one polypeptide (subunits); the way the folded subunits are arranged with respect to each other (linear string of spheres, spheres arranged one upon each other in the form of a cube or plate etc.) is the architecture of the protein. Adult human haemoglobin has 4 subunits — two of α type and two of β type.
| Level | What it describes | Bonds / features shown in Fig. 9.3 |
|---|---|---|
| Primary | Sequence of amino acids (N-terminal to C-terminal) | Peptide bonds |
| Secondary | Right-handed helix, other folded forms | α-helix, β-pleated sheet, hydrogen bonds |
| Tertiary | Folding upon itself into a 3-D ball | Disulphide bonds, hydrogen bonds etc. |
| Quaternary | Arrangement of several polypeptide subunits | e.g., haemoglobin: 2α + 2β |
9.8 Enzymes
- Almost all enzymes are proteins; some nucleic acids behave like enzymes — ribozymes.
- An enzyme, like any protein, has primary, secondary and tertiary structure. In the tertiary structure the chain criss-crosses itself and makes many crevices or pockets; one such pocket is the active site — the crevice into which the substrate fits. Through the active site enzymes catalyse reactions at a high rate.
- Enzymes vs inorganic catalysts: inorganic catalysts work efficiently at high temperature and pressure; enzymes get damaged at high temperature (say above 40°C). But enzymes from thermophilic organisms (hot vents, sulphur springs) remain stable and active up to 80–90°C — thermal stability is an important quality of such enzymes.
9.8.1 Chemical reactions
- A physical change is a change in shape without breaking of bonds (a change of state — ice to water, water to vapour — is also physical). When bonds are broken and new bonds formed, it is a chemical reaction: e.g., Ba(OH)2 + H2SO4 → BaSO4 + 2H2O (inorganic); hydrolysis of starch into glucose (organic).
- Rate of a process = amount of product formed per unit time, rate = δP/δt. If direction is specified, rate is called velocity.
- Rate is influenced by temperature among other factors; rule of thumb: rate doubles or halves for every 10°C change in either direction.
- Catalysed reactions proceed at vastly higher rates. Example: CO2 + H2O → H2CO3 (carbonic anhydrase). Uncatalysed: about 200 molecules of H2CO3 per hour; with carbonic anhydrase in the cytoplasm: about 600,000 molecules per second — acceleration of about 10 million times.
- A multistep reaction, each step catalysed by the same enzyme complex or different enzymes, is a metabolic pathway: glucose → 2 pyruvic acid through ten enzyme-catalysed reactions (glycolysis; see Chapter 12). With one or two additional reactions the same pathway gives lactic acid (skeletal muscle, anaerobic), pyruvic acid (normal aerobic) or ethanol (yeast fermentation) — different conditions, different products.
| Process | Change | Example |
|---|---|---|
| Physical | No bonds broken/formed; shape or state changes | Ice → water → vapour |
| Chemical | Bonds broken and new bonds formed | Hydrolysis of starch into glucose; Ba(OH)2 + H2SO4 → BaSO4 + 2H2O |
9.8.2 How do enzymes bring about such high rates of chemical conversions?
- The chemical converted into a product is the substrate (S); the enzyme (a protein with a 3-D structure including an active site) converts S into product P: S → P.
- The substrate must diffuse towards the active site and bind within the cleft — an obligatory, transient ES (enzyme–substrate) complex forms. During this state a new structure, the transition state structure, is formed; soon, after bond breaking/making, the product is released.
- The pathway must pass through the transition state; all other intermediate ‘altered structural states’ are unstable (stability relates to the energy status).
- In Fig. 9.4: y-axis = potential energy, x-axis = progress of the structural transformation. If P is lower than S the reaction is exothermic (no energy need be supplied by heating); either way S must pass through a much higher energy state, the transition state.
- Activation energy = difference in average energy content between S and the transition state. Enzymes bring down this energy barrier, making the transition of S to P easier.
9.8.3 Nature of enzyme action
- Each enzyme (E) has a substrate-binding site; a highly reactive enzyme–substrate complex (ES) is produced, which is short-lived and dissociates into product(s) P and the unchanged enzyme, via an intermediate enzyme–product complex (EP). The formation of ES is essential for catalysis.
- The substrate binds to the active site, fitting into it.
- Binding induces the enzyme to alter its shape, fitting more tightly around the substrate.
- The active site, now in close proximity to the substrate, breaks the chemical bonds of the substrate and the new enzyme–product complex is formed.
- The enzyme releases the products; the free enzyme is ready to bind another substrate molecule and run through the catalytic cycle again.
9.8.4 Factors affecting enzyme activity
- Activity can be affected by any change that can alter the tertiary structure: temperature, pH, substrate concentration, or binding of specific chemicals that regulate activity.
- Temperature and pH: enzymes function in a narrow range; each shows highest activity at an optimum temperature and optimum pH; activity declines on both sides. Low temperature preserves the enzyme in a temporarily inactive state, whereas high temperature destroys enzymatic activity because proteins are denatured by heat.
- Concentration of substrate: velocity rises at first with more substrate, then reaches a maximum velocity (Vmax) not exceeded by any further increase in substrate — because enzyme molecules are fewer than substrate molecules and, after saturation, no free enzyme molecules remain to bind the extra substrate. Km is the substrate concentration at which V = Vmax/2 (shown in Fig. 9.5c).
- Inhibition: when binding of a chemical shuts off enzyme activity it is inhibition and the chemical is an inhibitor. A competitive inhibitor closely resembles the substrate in structure and competes for the substrate-binding site; the substrate cannot bind and enzyme action declines — e.g., malonate inhibits succinic dehydrogenase (it resembles the substrate succinate). Competitive inhibitors are often used to control bacterial pathogens.
9.8.5 Classification and nomenclature of enzymes
- Thousands of enzymes are classified by the type of reaction they catalyse into 6 classes, each with 4–13 subclasses, and named accordingly by a four-digit number.
| Class | Reaction catalysed (NCERT) |
|---|---|
| 1. Oxidoreductases / dehydrogenases | Oxidoreduction between two substrates S and S′: S reduced + S′ oxidised → S oxidised + S′ reduced |
| 2. Transferases | Transfer of a group G (other than hydrogen) between a pair of substrates: S–G + S′ → S + S′–G |
| 3. Hydrolases | Hydrolysis of ester, ether, peptide, glycosidic, C–C, C–halide or P–N bonds |
| 4. Lyases | Removal of groups from substrates by mechanisms other than hydrolysis, leaving double bonds |
| 5. Isomerases | Inter-conversion of optical, geometric or positional isomers |
| 6. Ligases | Linking together of 2 compounds, e.g., joining of C–O, C–S, C–N, P–O etc. bonds |
9.8.6 Co-factors
- Enzymes are composed of one or several polypeptide chains; in many cases non-protein constituents called co-factors are bound to make the enzyme catalytically active. The protein portion is the apoenzyme. Catalytic activity is lost when the co-factor is removed.
- Three kinds of co-factors: prosthetic groups, co-enzymes and metal ions.
| Co-factor | Nature | Example (NCERT) |
|---|---|---|
| Prosthetic group | Organic; tightly bound to apoenzyme | Haem in peroxidase and catalase (breakdown of H2O2 to water and oxygen); part of the active site |
| Co-enzyme | Organic; association with apoenzyme is transient (during catalysis); serves in many different enzyme reactions; essential components are often vitamins | NAD and NADP contain the vitamin niacin |
| Metal ion | Forms coordination bonds with side chains at the active site and with the substrate | Zinc is a co-factor of carboxypeptidase |
What are macromolecules? Give examples.
Concept — macromolecules. When a living tissue is ground in trichloroacetic acid and strained, the thick slurry separates into an acid-soluble pool (the filtrate) and an acid-insoluble fraction (the retentate). The compounds of the acid-insoluble fraction have very high molecular weights — of the order of ten thousand daltons and above — and are called macromolecules or biomacromolecules. They are, with the exception of lipids, polymers built of repeating building blocks.
- Proteins — polypeptides, heteropolymers of 20 types of amino acids joined by peptide bonds (e.g., enzymes, collagen, insulin, antibodies, haemoglobin).
- Polysaccharides — long chains of monosaccharides (e.g., cellulose, starch, glycogen, inulin, chitin).
- Nucleic acids — polynucleotides, polymers of nucleotides (DNA and RNA).
- Lipids — separate with the acid-insoluble fraction only because membranes break into vesicles during grinding; their molecular weight does not exceed about 800 Da, so lipids are not strictly macromolecules.
| Feature | Micromolecules (biomolecules) | Macromolecules (biomacromolecules) |
|---|---|---|
| Fraction in the analysis | Acid-soluble pool (filtrate) | Acid-insoluble fraction (retentate) |
| Molecular weight | About 18 to about 800 Da (less than 1000 Da) | Ten thousand Da and above (except lipids) |
| Nature | Simple compounds, monomers | Polymers of monomers (except lipids) |
| Examples | Amino acids, monosaccharides, fatty acids, glycerol, nucleotides, nucleosides, nitrogen bases | Proteins, polysaccharides, nucleic acids (lipids associated through membranes) |
| Building blocks | — | Amino acids → proteins; sugars → polysaccharides; nucleotides → nucleic acids |
Extra depth. Macromolecules can be homopolymers (one kind of monomer repeated ‘n’ times, e.g., cellulose — only glucose) or heteropolymers (different monomers, e.g., proteins with 20 amino-acid types). Together with the acid-soluble pool (roughly the cytoplasmic composition) they represent the entire chemical composition of the tissue. The word ‘true macromolecular fraction’ in NCERT is used for polysaccharides, polypeptides and polynucleotides.
Conclusion: macromolecules are the high-molecular-weight (≥ 104 Da) polymeric compounds of the acid-insoluble fraction — proteins, polysaccharides and nucleic acids (with lipids associated through membranes).
What is meant by tertiary structure of proteins?
Concept — tertiary structure. A protein is a long heteropolymer thread of amino acids. Its primary structure is the sequence of amino acids, and parts of the thread are coiled as helices or folded into other forms in the secondary structure. In the tertiary structure the long protein chain is folded upon itself like a hollow woolen ball, giving the protein a 3-dimensional (three-dimensional) shape.
- It is the 3-D architecture of one polypeptide chain obtained by folding of the already helical/folded (secondary-structure) regions upon one another.
- The shape is held by hydrogen bonds, disulphide bonds and other interactions between the side chains (R groups) of amino acids that come close in space (Fig. 9.3 shows hydrogen and disulphide bonds).
- Folding of the chain makes crevices or pockets — in enzymes one such pocket is the active site into which the substrate fits.
- NCERT stresses that tertiary structure is absolutely necessary for the many biological activities of proteins; any change that alters it (heat, pH) destroys activity — the protein is denatured.
- When a protein has more than one polypeptide, the arrangement of the folded subunits is the quaternary structure (e.g., haemoglobin: 2α + 2β).
| Level | Meaning | Example / feature |
|---|---|---|
| Primary | Sequence of amino acids from N-terminal to C-terminal | Peptide-bonded chain |
| Secondary | Helix (right-handed) and other folded regions | α-helix, β-pleated sheet |
| Tertiary | Whole chain folded upon itself like a hollow woolen ball; 3-D view | Active-site pocket of an enzyme |
| Quaternary | Arrangement of several folded subunits | Haemoglobin (4 subunits) |
Extra depth. Only right-handed helices are seen in proteins. Because the tertiary structure creates the active site and binding pockets, a mutation that changes even one amino acid can change the folding and hence function. Proteins with a single polypeptide (monomeric) have no quaternary structure — their highest level is tertiary.
Conclusion: tertiary structure is the compact three-dimensional folding of a single polypeptide chain upon itself, essential for the biological activity of the protein.
Find and write down structures of 10 interesting small molecular weight biomolecules. Find if there is any industry which manufactures the compounds by isolation. Find out who are the buyers.
Concept — approach. This is a project question. Small molecular weight biomolecules (micromolecules, below 1000 Da) are the compounds of the acid-soluble pool; Figure 9.1 already shows several of them. Below are ten such compounds with their classes and formulae; the structures of the first eight are drawn in Figure 9.1 (including adenine, uracil, glucose, ribose, glycine/alanine/serine, palmitic acid, glycerol, nucleosides and nucleotide, cholesterol, lecithin) and the structure of alanine is redrawn in Q7.
| No. | Biomolecule | Class | Molecular formula | Industrial angle (generally known) |
|---|---|---|---|---|
| 1 | Glucose | Monosaccharide (sugar) | C6H12O6 | Obtained industrially by hydrolysis of starch; buyers: food, beverage, pharmaceutical (intravenous glucose) industries |
| 2 | Ribose | Pentose sugar of RNA | C5H10O5 | Fine-chemical suppliers; buyers: research labs, nucleoside/nucleotide and drug makers |
| 3 | Glycine | Amino acid (R = H) | C2H5NO2 | Produced for food/feed additives and pharma; buyers: food and pharma firms |
| 4 | Alanine | Amino acid (R = CH3) | C3H7NO2 | Used in nutrition and cell-culture media; buyers: pharma, biotech labs |
| 5 | Palmitic acid | Saturated fatty acid (16 C) | C16H32O2 | Obtained from palm oil and animal fat; buyers: soap, cosmetic and food industries |
| 6 | Glycerol | Trihydroxy propane (simple lipid) | C3H8O3 | By-product of fat/oil processing and soap making; buyers: cosmetics, pharma, food |
| 7 | Adenine | Purine nitrogen base | C5H5N5 | Fine-chemical suppliers; buyers: research and drug companies |
| 8 | Cholesterol | Steroid lipid | C27H46O | Isolated commercially from animal sources such as wool grease; buyers: pharma and cosmetic companies |
| 9 | Caffeine | Alkaloid (secondary metabolite) | C8H10N4O2 | Extracted from tea and coffee (e.g., during decaffeination); buyers: beverage and pharma industries |
| 10 | Morphine | Alkaloid (secondary metabolite) | C17H19NO3 | Isolated from opium poppy under licensed control; buyers: licensed pharmaceutical manufacturers (medical use) |
- How to find the structures: look up each compound in a biochemistry or organic-chemistry textbook, an encyclopaedia or a chemical database such as PubChem; draw the skeleton with all functional groups (–OH, –COOH, –NH2, rings).
- Industries that isolate biomolecules: pharmaceutical companies (alkaloids, steroids, vitamins), food and beverage industry (sugars, amino acids, caffeine), cosmetic and soap industry (glycerol, fatty acids, lecithin), fine-chemical/biochemical suppliers (amino acids, nucleotides, bases).
- Buyers: pharmaceutical firms, food processors, cosmetic makers, hospitals (e.g., intravenous fluids), educational and research laboratories. Exact company names and prices must be collected by your own survey (web / local industry) — the formulae above are standard textbook values.
Extra depth. Primary metabolites such as amino acids and sugars occur in all organisms, while secondary metabolites such as alkaloids (morphine, caffeine) are characteristic of particular plants and are often valuable drugs or stimulants (Table 9.3 of NCERT lists alkaloids such as morphine and codeine). Whether a compound is isolated or made by chemical/biological synthesis depends on cost: isolation is used when the compound is abundant in a natural source.
Conclusion: small molecular weight biomolecules such as sugars, amino acids, fatty acids, bases and alkaloids are routinely isolated or manufactured for the pharmaceutical, food, cosmetic and research markets.
Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (e.g., Cosmetics etc.)
Concept — approach. Proteins serve a variety of cellular functions: many are enzymes, some are antibodies, some are receptors, some are hormones and some are structural proteins (NCERT Table 9.5). Because of these functions, purified proteins are used as medicines and in industry.
| Protein | Use as a therapeutic agent (generally known) |
|---|---|
| Insulin | Hormone given to treat diabetes mellitus |
| Growth hormone (somatotropin) | Hormone given in growth-hormone deficiency |
| Antibodies / antivenom / vaccines’ antibody products | Protect against infectious agents and snake venom (Table 9.5: antibody fights infectious agents) |
| Interferons | Used against some viral infections and cancers |
| Streptokinase | Enzyme used to dissolve blood clots in heart attack |
| Clotting factor VIII | Given in haemophilia |
| Erythropoietin | Hormone used in some types of anaemia |
| Asparaginase / other therapeutic enzymes | Enzymes used in treating certain cancers or digestive disorders (e.g., trypsin/pancreatic enzymes in digestive supplements) |
| Albumin | Given to restore blood volume |
| Other applications | Protein and use |
|---|---|
| Cosmetics | Collagen and keratin-derived proteins in creams, shampoos and anti-ageing products |
| Food industry | Enzymes such as papain (meat tenderiser), rennet/chymosin (cheese making), proteases/amylases in baking and brewing |
| Detergents | Proteases and lipases in washing powders to remove protein and oil stains |
| Leather and textile | Proteases for bating; silk and wool are protein fibres |
| Surgery and medicine | Collagen and gelatin for sutures, capsules and wound dressings |
| Adhesives and others | Casein-based glues; gelatin in photography and desserts |
| Research / diagnostics | Enzymes and antibodies used in laboratory kits (e.g., pregnancy and disease tests) |
Extra depth. NCERT notes that some proteins carry nutrients across membranes, fight infection, act as hormones or enzymes. Therapeutic proteins must be produced in pure form; today many are made by genetic engineering in microbes rather than only by extraction (as you will study in biotechnology). The list above contains well-established uses; for local sources and prices consult pharmacy and industry catalogues, as the question asks you to find out.
Conclusion: purified proteins — insulin, antibodies, interferons, clotting factors and enzymes — are therapeutic agents, while collagen, keratin, enzymes and casein have cosmetic, food, detergent and other industrial uses.
Explain the composition of triglyceride.
Concept — triglyceride. Lipids are generally water-insoluble compounds. Many lipids contain both glycerol and fatty acids, the fatty acids being esterified with glycerol. A glyceride in which all three hydroxyl groups of glycerol are esterified with fatty acids is a triglyceride (Figure 9.1 shows a triglyceride with fatty acids R1, R2 and R3).
- Glycerol — a simple lipid, trihydroxy propane (C3H8O3), with three –OH groups.
- Fatty acids — a carboxyl group attached to an R group; R may be –CH3, –C2H5 or 1 to 19 –CH2 groups. Palmitic acid has 16 carbons (including the carboxyl carbon); arachidonic acid has 20. They may be saturated (no double bond) or unsaturated (one or more C=C).
- Linkage: the –COOH of each fatty acid combines with an –OH of glycerol to form an ester bond with loss of water. One fatty acid → monoglyceride; two → diglyceride; three → triglyceride.
- Triglycerides are also called fats and oils on the basis of melting point — oils have lower melting point (e.g., gingelly oil) and stay liquid in winter.
| Glyceride | Fatty acids esterified with glycerol | Free –OH groups of glycerol left |
|---|---|---|
| Monoglyceride | 1 | 2 |
| Diglyceride | 2 | 1 |
| Triglyceride | 3 (R1, R2, R3) | 0 |
Extra depth. R1, R2 and R3 may be identical or different fatty acids, so a great variety of triglycerides is possible. Phospholipids (such as lecithin) differ because one fatty-acid position is replaced by a phosphorylated organic compound. Lipids are not true macromolecules (molecular weight below about 800 Da) but come into the acid-insoluble fraction through membrane vesicles.
Conclusion: a triglyceride is composed of one molecule of glycerol esterified with three fatty-acid molecules (R1, R2, R3), formed with the loss of three water molecules.
Can you attempt building models of biomolecules using commercially available atomic models (Ball and Stick models).
Concept — yes, it can be done. Ball-and-stick kits represent atoms as coloured balls and bonds as sticks (or springs for double bonds), so the 3-D shape of a molecule can be built and handled. Starting from small molecules (water, glucose, an amino acid) one can progress to a short peptide.
- Material: a molecular-model kit with carbon (4 holes, usually black), hydrogen (1 hole, white), oxygen (2 holes, red), nitrogen (3 holes, blue), phosphorus and sulphur balls, and sticks/springs for single and double bonds. The colour code is the usual convention; check the colours supplied in your kit.
- Step 1 — decide the structure: take the structural formula from Figure 9.1 (e.g., alanine, glycine, glycerol, glucose, ribose, palmitic acid).
- Step 2 — skeleton: join the carbon balls with sticks to form the backbone or ring (the α-carbon of an amino acid is a tetrahedral carbon).
- Step 3 — substituents: attach –OH, –NH2, –COOH and R groups to the right carbons; use springs for C=O.
- Step 4 — fill valencies: put hydrogens on every remaining hole so each atom has its proper valency (C = 4, N = 3, O = 2, H = 1).
- Step 5 — check: compare the model with the structure and count atoms against the molecular formula.
- Step 6 — link units: join two amino-acid models by removing –OH from one carboxyl and H from the next amino group to show a peptide bond; similarly link glycerol with three fatty acids to show a triglyceride.
| Biomolecule | Model to build | What you learn |
|---|---|---|
| Amino acid (alanine) | α-carbon with H, –NH2, –COOH and –CH3 | Four different groups on the α-carbon |
| Glycerol + palmitic acid | Three-carbon chain, 3 –OH; 16-carbon fatty acid | Glycerol is trihydroxy propane; esterification |
| Glucose / ribose | Ring structures | Hexose vs pentose |
| Dipeptide | Two amino acids joined | Peptide bond |
Extra depth. NCERT notes that physicists think in three-dimensional views while organic chemists draw two-dimensional structures and biologists describe proteins at four levels; physical models bridge these views. Large molecules like proteins are modelled with computer software, but small biomolecules are ideal for kits.
Conclusion: yes — with ball-and-stick atomic models, small biomolecules such as amino acids, glycerol, fatty acids and sugars can be built by assembling atoms according to their valencies and checking against the structural formula.
Draw the structure of the amino acid, alanine.
Concept — α-amino acid. Amino acids are organic compounds containing an amino group and an acidic (carboxyl) group on the same carbon, the α-carbon. The four valency positions of this carbon are occupied by hydrogen, a carboxyl group, an amino group and a variable R group. In alanine the R group is a methyl group (–CH3).
- Formula: H2N–CH(CH3)–COOH; molecular formula C3H7NO2; IUPAC name 2-aminopropanoic acid.
- R group: R = H gives glycine, R = methyl gives alanine, R = hydroxy methyl gives serine (the three amino acids of Figure 9.1).
- Class: a neutral amino acid (one amino and one carboxyl group); NCERT lists valine as another neutral example.
- Ionisation: the –NH2 and –COOH are ionizable, so in solutions of different pH the structure changes; in the zwitterionic form the amino group is –NH3+ and the carboxyl group is –COO−.
| Amino acid | R group | Class (NCERT) |
|---|---|---|
| Glycine | –H | Neutral (simplest) |
| Alanine | –CH3 | Neutral |
| Serine | –CH2OH (hydroxy methyl) | Polar, hydroxyl-containing |
| Glutamic acid | — | Acidic |
| Lysine | — | Basic |
Extra depth. Amino acids are substituted methanes: the central carbon carries four different groups, so (except glycine, where R = H) the α-carbon is asymmetric. Twenty types of amino acids occur in proteins (e.g., alanine, cysteine, proline, tryptophan, lysine); some are essential (to be supplied in the diet) and some are non-essential.
Conclusion: alanine is the α-amino acid H2N–CH(CH3)–COOH, with a methyl group as its R group.
What are gums made of? Is Fevicol different?
Concept — gums. NCERT lists gums along with rubber and cellulose under the polymeric substances among the secondary metabolites (Table 9.3). Chemically, natural gums are polysaccharides — long chains of sugar units (monosaccharides) — obtained as exudates from plants. Polysaccharides are the ‘threads’ of sugars described in section 9.5.
- Natural gum: a plant-derived polysaccharide (polymer of sugars); it dissolves or swells in water to give a sticky, viscous mass. Examples of gum-yielding plants are the acacia/babul-type trees (gum arabic).
- Fevicol is a commercial synthetic adhesive — a white glue that is an aqueous emulsion of a synthetic polymer, polyvinyl acetate (PVA/PVAc), not a plant polysaccharide. Hence it is different from natural gum.
- Similarity: both are polymers that act as adhesives. Difference: gum is a biological secondary metabolite made of sugar units, while Fevicol is a man-made polymer made of vinyl acetate units.
| Feature | Natural gum | Fevicol (synthetic adhesive) |
|---|---|---|
| Source | Plants (exudate) | Manufactured in industry from petrochemical-derived monomer |
| Monomer | Sugars (monosaccharides) | Vinyl acetate |
| Nature | Polysaccharide (biological polymer) | Synthetic polymer (polyvinyl acetate emulsion) |
| NCERT category | Secondary metabolite, polymeric substance | Not a biomolecule |
| Biodegradability | Generally biodegradable | Largely persists longer in the environment |
Extra depth. Rubber (a polymeric secondary metabolite, from the latex of rubber plants) and cellulose are the other polymeric substances of Table 9.3. Natural gums are used as thickeners and stabilisers in foods and medicines; synthetic glues replaced many gums where stronger bonding or water resistance is needed. The statement that Fevicol is a PVAc emulsion is general industrial knowledge — check the label of the product you have.
Conclusion: gums are plant polysaccharides made of sugar units, whereas Fevicol is a synthetic polymer adhesive (polyvinyl acetate) — so yes, it is different.
Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.
Concept — qualitative tests. A qualitative test shows only the presence or absence of a class of biomolecule through a colour or visible change. The standard school-laboratory tests are given below (the exact observations depend on the sample you take).
| Biomolecule | Test | Procedure (brief) | Positive result |
|---|---|---|---|
| Proteins | Biuret test | 2 ml sample + 2 ml dil. NaOH, then a few drops of dilute copper sulphate solution; mix | Violet / purple colour |
| Amino acids | Ninhydrin test | Add a few drops of ninhydrin solution to the sample and warm in a water bath | Blue-purple colour (proline gives yellow) |
| Fats and oils | Grease-spot test; Sudan III (or IV) test | Rub the sample on filter paper and let it dry; or add Sudan stain to the sample | Translucent oily spot that does not disappear on drying; stain gives red/orange oily droplets |
| Reducing sugars (for comparison) | Benedict’s test | Sample + Benedict’s reagent, boil | Green to orange-red precipitate |
| Starch (for comparison) | Iodine test | Add a drop of iodine solution | Blue colour (starch–I2, section 9.5) |
| Sample | Likely observation (record your own) | Reason |
|---|---|---|
| Fruit juice | Reducing-sugar test strongly positive; proteins, fat and amino acids little or absent | Fruit juice is rich in sugars, with very little protein and fat |
| Saliva | Biuret/ninhydrin positive (weak); starch is digested with time | Saliva contains salivary enzyme (protein) and a small amount of amino compounds |
| Sweat | Mostly negative for proteins and fats; faint amino-acid reaction possible | Sweat is mostly water with salts and traces of other solutes |
| Urine (normal) | Proteins and fats normally negative; traces of amino compounds may appear | Normal urine is largely water, urea and salts — a protein-positive reaction can signal a disorder |
- Collect each sample in a clean test tube and label it.
- Run the biuret, ninhydrin and grease-spot/Sudan tests on each sample; include distilled water as a negative control and a known protein/oil as a positive control.
- Record the colour of each tube in a table and compare with the controls.
- Draw conclusions: which sample contains which biomolecule.
Extra depth. Use controls so that colour changes are real. Biuret detects peptide bonds (so it needs at least two peptide bonds — free amino acids do not give it), which is why amino acids need the separate ninhydrin test. These are class tests, not quantitative; NCERT only asks you to find and carry out such tests, so the table of observations is the expected pattern, not a fixed result.
Conclusion: biuret tests proteins, ninhydrin tests amino acids and Sudan / grease-spot tests fats and oils; each sample (fruit juice, saliva, sweat, urine) is tested and its colour change recorded against controls.
Find out how much cellulose is made by all the plants in the biosphere and compare it with how much of paper is manufactured by man and hence what is the consumption of plant material by man annually. What a loss of vegetation!
Concept — approach. Cellulose is a polysaccharide homopolymer of glucose; plant cell walls are made of cellulose, and paper from plant pulp and cotton fibre is cellulosic (section 9.5). The question asks for figures, which change with time; the values below are the commonly quoted order-of-magnitude estimates — you should check the latest data from reliable sources (FAO, paper-industry reports) before writing them in a project.
| Quantity | Commonly cited approximate estimate | Note |
|---|---|---|
| Cellulose synthesised by all plants in the biosphere per year | of the order of 1011 tonnes (about 100 billion tonnes) | Cellulose is the most abundant organic polymer on earth |
| Paper and paperboard manufactured by humans per year | of the order of 4 × 108 tonnes (about 400 million tonnes) | Industry figures for recent years are in this range |
| Ratio (paper : total cellulose) | of the order of one part in a few hundred (well below 1%) | Humans also use timber, fuel wood, cotton and food |
- Comparison: the paper made by humans is only a small fraction (well under one per cent) of the cellulose plants make each year — nature’s cellulose production is enormous.
- Consumption of plant material by man: includes paper and pulp, timber, fire-wood, cotton and other fibres, and the plants eaten as food and fodder; therefore the total annual consumption of plant material is much larger than paper alone.
- What a loss of vegetation: every tonne of paper needs plant pulp; cutting forests for pulp, timber and fuel reduces vegetation cover, which affects photosynthesis, carbon storage, soil protection and biodiversity.
- What can we do? use both sides of paper, recycle paper, use recycled or agro-waste based paper, reduce printing, plant trees and use sustainably managed pulp.
Extra depth. Because plants synthesise cellulose from glucose made in photosynthesis, using vegetation is also using stored solar energy and carbon. Recycling one lot of paper saves fresh pulp, so total plant consumption can fall without reducing paper use. The numerical estimates given are approximate; NCERT gives no figure, so state your source in a project.
Conclusion: plants make vastly more cellulose each year than humans turn into paper, but human use of plant material (paper, timber, fuel, food) is large enough to reduce vegetation, so conservation and recycling are necessary.
Describe the important properties of enzymes.
Concept — enzymes. Almost all enzymes are proteins (a few nucleic acids called ribozymes also act as enzymes). They are biological catalysts: each enzyme has a primary, secondary and tertiary structure and its tertiary folding creates crevices, one of which is the active site into which the substrate fits.
- Protein nature: enzymes are proteins with a 3-D structure (exceptions — ribozymes); loss of the tertiary structure (denaturation) destroys activity.
- Very high catalytic power: carbonic anhydrase forms about 600,000 molecules of H2CO3 per second against about 200 per hour uncatalysed — roughly 10 million times faster.
- Lower the activation energy: the enzyme binds the substrate at the active site, forms the ES complex and passes through a transition state with a smaller energy barrier (Fig. 9.4).
- Active site and specificity: the substrate fits the active site; binding induces a change in enzyme shape so that it fits more tightly around the substrate.
- Not consumed: the enzyme is released unchanged (E + S → ES → EP → E + P) and is ready to bind another substrate molecule.
- Optimum temperature and pH: each enzyme shows maximum activity at a particular temperature and pH; low temperature keeps it temporarily inactive and high temperature denatures it (Fig. 9.5).
- Thermal sensitivity vs thermostability: most enzymes are damaged above about 40°C, unlike inorganic catalysts; enzymes of thermophilic organisms remain active up to 80–90°C.
- Substrate concentration: velocity rises and reaches Vmax after saturation of enzyme molecules.
- Inhibition: a competitive inhibitor resembling the substrate (e.g., malonate for succinic dehydrogenase) competes for the active site and reduces activity.
- Co-factors: many enzymes need a non-protein co-factor (prosthetic group, co-enzyme or metal ion); the protein part is the apoenzyme.
- Classification: 6 classes — oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases.
| Property | Enzymes | Inorganic catalysts |
|---|---|---|
| Chemical nature | Proteins (and ribozymes) | Metals / inorganic compounds |
| Temperature | Damaged above about 40°C (except enzymes of thermophiles) | Work efficiently at high temperature and pressure |
| Active site | Substrate binds at a pocket formed by tertiary folding | No such protein pocket |
| Rate | Enormous acceleration (e.g., about 107 times for carbonic anhydrase) | Catalyse, usually under harsh conditions |
Extra depth. The enzyme does not change the energy difference between substrate and product (whether the reaction is exothermic or endothermic); it only lowers the activation energy. Rate roughly doubles or halves for every 10°C change, but above the optimum the loss of structure dominates. A multi-step metabolic pathway such as glucose to pyruvic acid needs ten enzyme-catalysed reactions; with one or two extra steps the same pathway gives lactic acid, or ethanol in yeast.
Conclusion: enzymes are mainly protein catalysts with an active site that lower activation energy, remain unchanged, work best at optimum temperature and pH, and are controlled by inhibitors and co-factors.