Chapter 13 — Biomolecules

Fig 1 — Educational Diagram: Introduction to Biomolecules

What are biomolecules?
Biomolecules are organic molecules produced by living organisms that perform structural, catalytic and regulatory roles. They are mainly composed of C, H, O, N, P and S. Major classes are carbohydrates, proteins, lipids and nucleic acids.

Classification and building blocks

• Carbohydrates – composed of monosaccharide units (monomers) like glucose. Functions: energy source (glucose), storage (starch, glycogen) and structure (cellulose).
• Proteins – polymers of amino acids linked by peptide bonds. Functions: enzymes, structural proteins, transport (hemoglobin), hormones (insulin), immune molecules.
• Lipids – hydrophobic molecules (triglycerides, phospholipids, steroids). Functions: energy storage, membrane structure (phospholipids), signaling (steroids).
• Nucleic acids – DNA and RNA built from nucleotides (base + sugar + phosphate). Function: storage and expression of genetic information.

Monomer → Polymer relationships
Biomolecules often follow monomer→polymer patterns: monosaccharide → polysaccharide, amino acid → polypeptide → protein, nucleotide → polynucleotide.

Key chemical features

• Condensation (dehydration) reactions form bonds (glycosidic, peptide, ester, phosphodiester) with release of H2O; hydrolysis reverses them.
• Functional groups (–OH, –COOH, –NH2, phosphate) determine reactivity and interactions (H‑bonding, ionic, hydrophobic).
• Proteins fold into secondary, tertiary and quaternary structures stabilized by H‑bonds, ionic and hydrophobic interactions and disulfide bridges.

Biological importance and properties

• Specificity: enzymes (proteins) accelerate reactions with high specificity.
• Solubility: many small biomolecules are water soluble; large hydrophobic lipids are not, which drives membrane formation.
• Sensing and regulation: hormones, receptors and nucleic acids control cellular processes.

Common qualitative tests (practical relevance)

• Benedict's test: reducing sugars (glucose) give red precipitate.
• Iodine test: starch gives blue-black color.
• Biuret test: proteins give violet colour.
• Sudan III: lipids stain red/orange.

Summary
Understanding biomolecules means recognizing their basic monomers, the kinds of bonds that link them, how structure relates to function, and examples of their roles in living systems.

Fig 2 — Educational Diagram: Carbohydrates

Definition: Carbohydrates are polyhydroxy aldehydes or ketones and their derivatives (or substances that produce such compounds on hydrolysis). General empirical formula is often written as Cn(H2O)m; simplest monosaccharides follow CnH2nOn.

Classification:

• Monosaccharides – simplest sugars (cannot be hydrolysed): e.g. glucose (an aldohexose), fructose (a ketohexose). They show stereoisomerism (D/L), anomerism (α/β) and mutarotation (interconversion of anomers in solution).
• Oligosaccharides – 2–10 monosaccharide units joined by glycosidic bonds: disaccharides like sucrose, maltose, lactose.
• Polysaccharides – long chains: starch (amylose + amylopectin), glycogen, cellulose, chitin (structural or storage roles).

Structures & Stereochemistry:

• Fischer projection to Haworth (ring) conversion: intramolecular hemiacetal (aldoses) or hemiketal (ketoses) formation gives pyranoses (6-membered) or furanoses (5-membered).
• Alpha (α) vs Beta (β) anomers differ in configuration at the anomeric carbon (C-1 for aldoses). Example: in D-glucopyranose, α has OH down, β has OH up (in Haworth conventional drawing).
• D/L designation is based on configuration of the highest-numbered chiral center (D = same as D-glyceraldehyde). Number of possible stereoisomers = 2^n (n = number of chiral centres). For aldohexoses, n = 4 so 16 stereoisomers.

Chemical properties & Reactions:

• Reducing vs Non-reducing sugars: Reducing sugars have a free hemiacetal/aldehyde group and give positive Benedict's/Fehling's test. Examples: glucose (reducing), maltose (reducing). Sucrose is non-reducing (both anomeric carbons involved in glycosidic bond).
• Mutarotation: change in optical rotation as α and β anomers equilibrate in water (e.g., D-glucose equilibrium ~36% α and 64% β at 20°C).
• Glycosidic bond formation (condensation): Monosaccharide-OH + monosaccharide-OH → glycoside (–O–) + H2O. Hydrolysis reverses it (acid/enzyme).
• Oxidation / Reduction: Aldehyde group oxidised to carboxylic acid (e.g., glucose → gluconic acid). Reduction of carbonyl yields alditols (e.g., glucose → sorbitol).
• Characteristic tests: Benedict's/Fehling's (reducing sugars), Tollen's (aldehydes), formation of osazones with phenylhydrazine, saponification/hydrolysis of glycosides.

Biological roles:

• Primary energy source: glucose metabolized in glycolysis and respiration.
• Storage: starch (plants), glycogen (animals).
• Structural: cellulose (plant cell walls), chitin (arthropod exoskeletons).
• Recognition & signalling: glycoproteins and glycolipids on cell surfaces.

Important notes for Class 12:

• Know structures and distinguishing tests for glucose, fructose, galactose, sucrose, lactose, maltose, starch, glycogen and cellulose.
• Be able to draw Fischer and Haworth structures for glucose and fructose and show formation of maltose or sucrose glycosidic linkages (α or β specified).
• Understand mutarotation, reducing/non-reducing behaviour and basic reactions (oxidation, reduction, osazone formation).

Fig 3 — Educational Diagram: Amino Acids and Proteins

Definition & basic structure
Amino acids are organic compounds that contain an amino group (−NH2), a carboxyl group (−COOH), a hydrogen atom and a variable side chain (R) all bonded to a central (alpha) carbon: H2N–CHR–COOH. When in aqueous solution at physiological pH most amino acids exist as zwitterions (NH3+ and COO−).

Classification

• By nature of R group: nonpolar (hydrophobic) e.g. Leu, Val; polar uncharged e.g. Ser, Thr; acidic (negatively charged) e.g. Asp, Glu; basic (positively charged) e.g. Lys, Arg.
• By essentiality: essential (must be obtained from diet) vs non‑essential (synthesised in body).
• Special cases: Glycine is achiral (R = H); Proline is imino acid (cyclic side chain affecting backbone conformation).

Acid–base behaviour and zwitterion
Amino acids are amphoteric: they can act as acids or bases. In acidic medium they are cationic (NH3+ COOH), in basic medium anionic (NH2 COO−), and at an intermediate pH (isoelectric point, pI) they carry no net charge (zwitterion). The Henderson–Hasselbalch relation applies to the ionisable groups: pH = pKa + log([A−]/[HA]).

Isoelectric point (pI)
For amino acids without ionisable side chains, pI = (pKa,COOH + pKa,NH3+)/2. For acidic amino acids approximate pI = (pKa,COOH + pKa,side chain)/2; for basic amino acids pI ≈ (pKa,NH3+ + pKa,side chain)/2. At pH = pI the net charge is zero and amino acid shows minimal electrophoretic mobility.

Peptide bond & polypeptides
A peptide bond (CONH) forms by condensation between the −COOH of one amino acid and the −NH2 of another: amino acid(n) → polypeptide + (n−1) H2O. The C–N peptide bond has partial double‑bond character (resonance), making it planar and restricting rotation.

Protein structure levels

• Primary: linear sequence of amino acids (peptide chain).
• Secondary: local regular structures stabilised by H‑bonds — alpha helix (H‑bond i → i+4) and beta sheet (antiparallel/parallel H‑bonding), turns and loops.
• Tertiary: 3D folding of a single polypeptide due to hydrophobic interactions, disulfide bonds (—S—S—), ionic interactions, hydrogen bonds and van der Waals forces.
• Quaternary: assembly of multiple polypeptide subunits (e.g., hemoglobin is α2β2).

Protein properties and reactions
- Denaturation: loss of secondary/tertiary/quaternary structure (heat, pH, organic solvents, urea, detergents) usually with loss of function. Some denaturation is irreversible.
- Hydrolysis: proteins can be hydrolysed to peptides and amino acids by strong acids/bases or proteolytic enzymes (pepsin, trypsin).
- Biological functions: enzymes (catalysis), transport (hemoglobin), hormones (insulin), structural (collagen, keratin), storage (ferritin), immune (antibodies), receptors, etc.

Analytical tests & estimation
- Biuret test: peptide bonds give violet colour with Cu2+ in alkaline medium (qualitative for proteins).
- Ninhydrin: reacts with free amino groups to give Ruhemann’s purple (qualitative/used in amino acid analysis).
- Xanthoproteic test: aromatic residues give yellow nitration product with conc. HNO3.
- UV absorption: aromatic amino acids (Trp, Tyr, Phe) absorb at ~280 nm — used with Beer–Lambert law (A = εcl) to estimate protein concentration.
- Electrophoresis (native PAGE) and SDS–PAGE (separates subunits by molecular weight) are routine separation/analysis methods.

Sequence determination & synthesis
- Edman degradation: sequential removal and identification of N‑terminal residues for short peptides. Modern methods: mass spectrometry (MS) and automated sequencing.
- Peptide synthesis: solid‑phase peptide synthesis (SPPS) allows stepwise assembly of peptides in vitro.

Important notes for Class 12
- Remember that pI depends on the pKa values of all ionisable groups. Titration curves of amino acids show plateaus at pKa values and a horizontal inflection near pI. Peptide bonds are formed by condensation and broken by hydrolysis. Protein function is dependent on correct 3D structure; small sequence changes can lead to disease (example: sickle cell anemia).

Fig 4 — Educational Diagram: Enzymes

Definition: Enzymes are biological catalysts—mostly globular proteins—that speed up biochemical reactions without being consumed. They lower the activation energy and increase reaction rates under mild biological conditions.

Structure & active site: Enzymes have specific three-dimensional structures (primary → quaternary). A small region called the active site binds substrate(s) and converts them to product(s). The active site provides precise orientation and chemical environment for catalysis.

Specificity & binding models: Enzyme specificity arises from complementary shape and interactions between enzyme and substrate. Two classic models explain binding:

• Lock-and-key: active site exactly matches substrate shape.
• Induced-fit: binding induces a conformational change in the enzyme to better fit the substrate.

Classification (by type of reaction): oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases.

Cofactors and coenzymes: Some enzymes require non-protein helpers. Metal ions or organic molecules (coenzymes like NAD+, FAD, coenzyme A, vitamins) participate in catalysis.

Factors affecting enzyme activity:

• Temperature: activity increases with temperature up to an optimum; above that the enzyme denatures (sharp fall).
• pH: each enzyme has an optimum pH; deviations alter ionization and structure.
• Substrate concentration: at low [S], rate ∝ [S]; at high [S] the enzyme becomes saturated and reaches a maximum velocity (Vmax).
• Inhibitors: molecules that reduce activity (competitive, noncompetitive, uncompetitive).

Enzyme kinetics — Michaelis–Menten framework: For a simple enzymatic reaction E + S ⇌ ES → E + P (rate constants k1, k−1, kcat), the initial rate v0 is given by the Michaelis–Menten equation:

v0 = (Vmax [S]) / (Km + [S])

Here Vmax is the maximum rate when enzyme is saturated, and Km (Michaelis constant) is the substrate concentration at which v0 = Vmax/2; Km reflects affinity (lower Km → higher affinity).

Derived parameters: turnover number kcat = Vmax / [E]t (molecules of substrate converted per enzyme active site per unit time). Catalytic efficiency = kcat / Km.

Types of inhibition:

• Competitive: inhibitor competes with substrate for active site; apparent Km increases, Vmax unchanged.
• Noncompetitive (mixed): inhibitor binds enzyme (or ES) at other site; Vmax decreases, Km may remain same (pure noncompetitive) or change (mixed).
• Uncompetitive: inhibitor binds only to ES complex; both Km and Vmax decrease.

Regulation: Enzymes are regulated by allosteric effectors (activators/inhibitors), covalent modification (phosphorylation), zymogen activation (inactive precursors activated when needed), and gene-level control of enzyme concentration.

Applications: enzymes are central to digestion, metabolism, clinical diagnostics (enzyme markers), industrial processes (detergents, food processing), biotechnology (PCR uses Taq DNA polymerase), and therapeutics (enzyme replacement, thrombolytics).

Practical notes for students: Understand graphs (rate vs [S], rate vs temperature/pH), be able to apply Michaelis–Menten and Lineweaver–Burk plots, and predict effects of inhibitors on Km and Vmax.

Fig 5 — Educational Diagram: Vitamins

What are vitamins?
Vitamins are organic micronutrients required in small amounts for normal growth, metabolism and maintenance of health. Most vitamins cannot be synthesized (in adequate amounts) by the human body and must be obtained from the diet.

Classification

• Fat-soluble vitamins: A, D, E, K (soluble in fats/oils; stored in liver and adipose tissue).
• Water-soluble vitamins: Vitamin C and B-complex (B1, B2, B3, B5, B6, B7, B9, B12) (dissolve in water; not stored appreciably; excess excreted in urine).

General chemical nature & properties
Most vitamins are small organic molecules (some complex, e.g. B12). They act as coenzymes or precursors of coenzymes, participate in enzymatic reactions (redox, transfer, decarboxylation). They are required in microgram to milligram amounts. Many are unstable to heat, light, alkalinity, oxidation.

Biochemical roles (highlights)

• Coenzymes: B-complex vitamins form coenzymes used by enzymes in metabolism (e.g., thiamine pyrophosphate from B1 for decarboxylation; FAD from riboflavin (B2); NAD+ from niacin (B3); CoA from pantothenic acid (B5); PLP from B6).
• Antioxidant: Vitamin E protects membranes; vitamin C regenerates reduced vitamin E and acts as a reducing agent.
• Hormone-like actions: Vitamin D regulates Ca2+ and phosphate metabolism; vitamin A (retinoids) regulate vision and gene expression.
• Blood clotting: Vitamin K is required for γ-carboxylation of clotting factors.

Important vitamins — functions, sources, deficiency

• Vitamin A (retinol): Vision (retinal), epithelial integrity, growth. Sources: liver, carrots, leafy greens, milk. Deficiency → night blindness, xerophthalmia.
• Vitamin D (calciferols): Ca/P homeostasis, bone mineralization. Sources: sunlight (skin), fortified milk, fish liver oils. Deficiency → rickets (children), osteomalacia (adults).
• Vitamin E (tocopherols): Lipid antioxidant; protects RBCs and membranes. Sources: vegetable oils, nuts. Deficiency → hemolytic anemia (rare).
• Vitamin K: γ-carboxylation of clotting factors (II, VII, IX, X). Sources: leafy greens, gut bacteria. Deficiency → bleeding tendency.
• Vitamin C (ascorbic acid): Antioxidant, collagen synthesis (hydroxylation of proline/lysine), iron absorption. Sources: citrus fruits, tomatoes, green vegetables. Deficiency → scurvy (bleeding gums, poor wound healing).
• Thiamine (B1): Forms TPP (thiamine pyrophosphate) used in decarboxylations. Sources: whole grains, meat. Deficiency → beriberi, Wernicke–Korsakoff syndrome.
• Riboflavin (B2): Precursor of FAD/FMN (redox). Sources: milk, eggs, green vegetables. Deficiency → angular stomatitis, cheilosis.
• Niacin (B3): Precursor of NAD+/NADP+ (redox). Sources: meat, legumes, cereals. Deficiency → pellagra (diarrhea, dermatitis, dementia).
• Pantothenic acid (B5): Component of CoA. Sources: widespread in foods. Deficiency → rare, general fatigue.
• Pyridoxine (B6): PLP coenzyme in amino acid metabolism. Sources: meat, bananas. Deficiency → anemia, neuropathy.
• Biotin (B7): Carboxylase cofactor. Sources: egg yolk, liver. Deficiency → dermatitis, hair loss (rare).
• Folate (B9): One-carbon transfers; DNA synthesis (important in pregnancy). Sources: leafy greens, legumes. Deficiency → megaloblastic anemia, neural-tube defects in fetus.
• Cobalamin (B12): DNA synthesis, methylation, neurological function. Sources: animal products. Deficiency → pernicious anemia, neurological signs.

Stability, interactions, toxicity
Water-soluble vitamins are generally less toxic because excess is excreted, but very high doses can still cause harm (e.g., B6 neuropathy). Fat-soluble vitamins can accumulate and cause hypervitaminosis (e.g., excess vitamin A → teratogenic effects; excess vitamin D → hypercalcemia).

Applications & public health
Vitamin supplementation and food fortification (iodized salt, vitamin D in milk, folic acid in flour) prevent deficiency diseases. Clinical use includes replacement therapy, prenatal supplements, and treatment of deficiency states.

Fig 6 — Educational Diagram: Nucleic Acids

Definition and components: Nucleic acids are biopolymers made of nucleotide monomers. Each nucleotide consists of three parts: a nitrogenous base (purine: adenine, guanine; pyrimidine: cytosine, thymine in DNA, uracil in RNA), a pentose sugar (deoxyribose in DNA, ribose in RNA) and one or more phosphate groups.

Nucleoside vs nucleotide: A nucleoside = base + sugar. A nucleotide = nucleoside + phosphate.

Primary structure: Nucleotides are linked by 3′–5′ phosphodiester bonds between the 3′-OH of one sugar and the 5′-phosphate of the next, producing a sugar-phosphate backbone with directionality (5′ → 3′).

Secondary structure of DNA: DNA commonly exists as a right-handed double helix (B-DNA) composed of two antiparallel polynucleotide strands. Bases pair by hydrogen bonding: A pairs with T (2 H-bonds), G pairs with C (3 H-bonds). The helix has major and minor grooves, base stacking (3.4 Å between adjacent bases) and one full turn ≈ 10 bp (≈ 3.4 nm).

RNA structures: RNA is usually single-stranded but folds into secondary structures (hairpins, stems, loops) via intramolecular base pairing. Types of RNA include mRNA, tRNA, rRNA and regulatory RNAs.

Key principles:

• Chargaff's rules: In double-stranded DNA, %A = %T and %G = %C; A+G = T+C.
• Directionality: replication and transcription proceed 5′ → 3′.
• Stability: DNA is more chemically stable than RNA because deoxyribose lacks the 2′-OH; RNA is prone to alkaline hydrolysis.

Functions:

• DNA: long-term storage of genetic information and transmission to progeny.
• RNA: carries genetic information for protein synthesis (mRNA), helps translate code (tRNA, rRNA), and plays regulatory and catalytic roles (ribozymes, snRNA).
• Cofactors and energy carriers: several nucleotides act as cofactors (NAD+, FAD) or energy currency (ATP).

Reactions and enzymology: DNA replication, transcription and repair are enzyme-mediated (DNA/RNA polymerases, ligases, nucleases). RNA can be cleaved non-enzymatically under alkaline conditions due to 2′-OH mediated intramolecular attack; DNases hydrolyze DNA phosphodiester bonds enzymatically.

Physical properties and experimental observations: Nucleic acids absorb strongly at 260 nm; denaturation (strand separation) causes a hyperchromic shift (increase in A260). Melting temperature (Tm) depends on GC content, ionic strength and length.

Biological and practical importance: Understanding nucleic acids underlies molecular biology techniques (PCR, DNA sequencing, cloning, gel electrophoresis), medical advances (genetic testing, mRNA vaccines), forensic science (DNA fingerprinting) and biotechnology.

Fig 7 — Educational Diagram: Qualitative Tests and Reactions for Biomolecules

Overview
Qualitative tests for biomolecules are simple wet-chemical assays used to detect the presence and certain functional groups of carbohydrates, proteins, lipids and nucleic acids. These tests rely on characteristic chemical reactions (e.g., oxidation–reduction, dehydration, complex formation, nitration) that give diagnostic colour changes or precipitates.

1. Carbohydrates

• Principle: Many tests depend on dehydration of sugars to furfural derivatives, reduction of metal ions by reducing sugars, or complex formation with iodine.
• Molisch's test (general test for carbohydrates): Conc. H2SO4 dehydrated sugar → furfural (or hydroxymethylfurfural) which condenses with α-naphthol to give a purple/violet ring at the acid–reagent interface. Positive for mono-, di- and polysaccharides.
• Benedict's/Fehling's test (reducing sugars): Aldehyde groups (or sugars that form aldehydes on ring-opening) reduce Cu2+ to red Cu2O precipitate in alkaline medium. Positive: glucose, lactose, maltose (not sucrose unless hydrolysed).
• Tollens' test (aldehydes): Aldehydes reduce [Ag(NH3)2]+ to metallic silver (silver mirror). Used to confirm reducing aldehydes.
• Seliwanoff's test (aldoses vs ketoses): Ketoses (e.g., fructose) dehydrate faster in acid to give furfural-type products that react with resorcinol (or similar) to give a cherry-red colour; aldoses give much slower / faint reaction.
• Bial's (Orcinol) test (pentoses): Pentoses form furfural derivatives on dehydration that react with orcinol + FeCl3 to give a green colour.
• Iodine test (starch): Iodine–iodide forms a blue-black complex with amylose (starch), negative with simple sugars.
• Distinguishing reducing vs non-reducing: If a carbohydrate is non-reducing (e.g., sucrose) it gives negative Benedict; after acid hydrolysis (HCl + heat) it yields reducing monosaccharides and then gives positive Benedict.

2. Proteins and Amino Acids

• Principle: Tests target peptide bonds, aromatic residues, free amino groups, and sulphur-containing residues.
• Biuret test: Peptide bonds complex with Cu2+ in alkaline medium to give violet/pink-violet colour. Positive for peptides and proteins (minimum ~2–3 peptide bonds).
• Ninhydrin test: Free α-amino groups react to give Ruhemann's purple (deep blue-violet). Proline (secondary amine) gives yellow.
• Xanthoproteic test: Aromatic amino acids (Tyr, Trp, Phe) are nitrated by conc. HNO3 → yellow; on adding alkali colour shifts to orange.
• Millon's reagent: Tyrosine residues give a red coloration (or red precipitate) due to phenolic group reactions.
• Hopkins–Cole test: Tryptophan gives a violet ring with glyoxylic acid in conc. H2SO4 (qualitative for indole ring).
• Tests for sulphur: Sodium nitroprusside or lead acetate tests can indicate presence of –SH (cysteine) or sulphur-containing residues (black precipitate with H2S or coloured reactions depending on reagent).

3. Lipids (fats and oils)

• Principle: Lipids are non-polar and soluble in organic solvents; they do not dissolve in water and give characteristic staining or translucency.
• Grease spot (paper) test: Lipid leaves a translucent, permanent grease spot on paper after drying.
• Emulsion test: Shake sample with ethanol, filter and add water → milky emulsion indicates lipid droplets.
• Sudan III / IV or Sudan Black test: Lipid-specific dyes stain fats red/black; used microscopically and in food tests.

4. Nucleic acids

• Diphenylamine (Dische) test: Deoxyribose (DNA) on dehydration forms a compound that reacts with diphenylamine in strong acid to give blue colour (used qualitatively for DNA).
• Bial's test (orcinol): Pentoses (ribose) give a green colour — useful for ribose detection (RNA).

Practical notes and controls

• Always run a blank/control and a known positive (standard) simultaneously.
• Many tests are destructive (use of conc. acids, oxidants). Interpret colours against standards under same lighting.
• Some tests can be confirmed by complementary assays (e.g., sucrose: negative Benedict but positive after acid hydrolysis).

Summary table (quick cues) — purple (Molisch) = carbohydrate present; red Cu2O (Benedict/Fehling) = reducing sugar; blue-black (iodine) = starch; violet (Biuret) = peptide bonds/protein; purple (Ninhydrin) = free amino groups; grease spot / Sudan red = lipids; blue (Diphenylamine) = DNA.

Fig 8 — Educational Diagram: Biological Importance and Applications

Overview

Biomolecules — carbohydrates, proteins, lipids, nucleic acids, vitamins and enzymes — are organic molecules essential for structure, function and regulation of living systems. Their chemical properties determine biological roles such as energy storage, catalysis, information storage and cell structure. Understanding their importance links chemistry to physiology, medicine and biotechnology.

Biological importance by class of biomolecule

• Carbohydrates: Immediate and short-term energy sources (glucose); storage polysaccharides (starch in plants, glycogen in animals); structural polysaccharides (cellulose in plant cell walls, chitin in arthropods). Also cell-recognition (glycoproteins).
• Proteins: Structural (collagen, keratin), transport (hemoglobin, membrane carriers), enzymes (biological catalysts that lower activation energy), hormones (insulin), antibodies (immune defense), receptors and motor proteins (myosin).
• Lipids: Energy-rich storage (triacylglycerols), membrane components (phospholipids, cholesterol) controlling fluidity and signalling (steroid hormones, prostaglandins), thermal insulation and protection.
• Nucleic acids: DNA stores genetic information; RNA (mRNA, tRNA, rRNA) decodes information for protein synthesis. Nucleotides also participate in energy transfer (ATP) and signaling (cAMP).
• Vitamins & coenzymes: Small organic molecules required in trace amounts; many act as enzyme cofactors (e.g., NAD+, FAD, coenzyme A) and antioxidants (vitamin C) or are essential for metabolism (vitamin B complex).
• Enzymes: Highly specific catalysts; regulate metabolism, signal transduction, DNA replication and repair. Enzyme activity depends on temperature, pH and substrate concentration.

Applications

• Medicine & diagnostics: Enzymes and antibodies in ELISA tests; PCR (DNA amplification) for diagnostics; recombinant proteins (insulin) for therapy; enzyme inhibitors as drugs (statins inhibit HMG-CoA reductase).
• Industry & biotechnology: Industrial enzymes: amylases (starch processing & brewing), proteases (detergents), lipases (fat processing, biodiesel). Fermentation and recombinant DNA technologies produce enzymes, antibiotics and vaccines.
• Food: Starch modification, cheese production (enzymes), fermentation (yeast), preservatives and vitamin fortification.
• Agriculture & environment: Biofertilizers, enzyme-based pesticide degradation, bioremediation using microorganisms that degrade pollutants.
• Research & forensic science: DNA sequencing, restriction enzymes for cloning, electrophoresis, spectrophotometric assays (Beer–Lambert law) for concentration measurements.

Key chemical concepts that connect function to structure

• Bond types: Glycosidic (carbohydrates), peptide (proteins), ester (lipids), phosphodiester (nucleic acids). Condensation (dehydration) builds polymers; hydrolysis breaks them.
• Noncovalent interactions (H-bonds, ionic, van der Waals, hydrophobic effect) determine 3D structures and molecular recognition (enzyme–substrate, antigen–antibody).
• Thermodynamics and kinetics: ATP hydrolysis provides free energy; enzymes change reaction rates without changing equilibrium.

Practical notes for students

• Relate structure to role: e.g., branching in glycogen speeds mobilization; double bonds in fatty acids affect membrane fluidity.
• Consider environmental effects: pH and temperature changes can denature proteins and inactivate enzymes (basis of sterilization and food preservation).
• Link laboratory methods to applications: spectrophotometry for concentration, electrophoresis for DNA/protein separation, chromatography for purification.

In summary, biomolecules are central to life processes and their chemical behavior underpins medical, industrial and environmental applications. Mastery of basic reactions (condensation/hydrolysis), enzyme behaviour and analytical formulas connects textbook chemistry to real-world technologies.