Carbohydrates – Complete Biochemistry Lecture Notes

1 Introduction & Definition

Carbohydrates (saccharides) are the most abundant organic biomolecules on Earth, defined by the empirical formula (CH₂O)_n, reflecting an equal ratio of carbon to water molecules. The term "carbohydrate" literally means hydrates of carbon.

📌 General Formula

C_n(H₂O)_n — where n ranges from 3 (trioses) to millions (cellulose). More precisely, monosaccharides follow C_nH_2nO_n.

Key Characteristics

Composed of C, H, and O (ratio H:O = 2:1)
Most are sweet-tasting, water-soluble, crystalline solids (simple forms)
Serve as the primary energy currency of all living cells
Play crucial structural, signaling, and immunological roles
Also called glycans when referring to polysaccharide chains

2 Classification of Carbohydrates

CLASSIFICATION FLOWCHART

CARBOHYDRATES — C_n(H₂O)_n

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MONOSACCHARIDES
cannot be hydrolysed

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Triose (C₃)

Tetrose (C₄)

Pentose (C₅)

Hexose (C₆)

Heptose (C₇)

OLIGOSACCHARIDES
2–10 monosaccharide units

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Disaccharides (2)

Trisaccharides (3)

Tetrasaccharides (4)

POLYSACCHARIDES
>10 monosaccharide units

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Homopolysaccharides

Heteropolysaccharides

Category	Units	Formula	Key Examples	Solubility
Monosaccharides	1	C_nH_2nO_n	Glucose, Fructose, Ribose	Soluble, sweet
Disaccharides	2	C₁₂H₂₂O₁₁	Sucrose, Maltose, Lactose	Soluble, sweet
Oligosaccharides	3–10	Variable	Raffinose, Stachyose	Partially soluble
Polysaccharides	>10	(C₆H₁₀O₅)_n	Starch, Glycogen, Cellulose	Insoluble/colloidal

3 Monosaccharides – Formulas & Structures

3.1 Molecular Formulas

Sugar	Type	Molecular Formula	Carbon #	Functional Group
Glyceraldehyde	Triose, Aldose	C₃H₆O₃	3	–CHO
Dihydroxyacetone	Triose, Ketose	C₃H₆O₃	3	C=O
Erythrose	Tetrose, Aldose	C₄H₈O₄	4	–CHO
Ribose	Pentose, Aldose	C₅H₁₀O₅	5	–CHO
Deoxyribose	Pentose, Aldose	C₅H₁₀O₄	5	–CHO
Glucose	Hexose, Aldose	C₆H₁₂O₆	6	–CHO at C1
Fructose	Hexose, Ketose	C₆H₁₂O₆	6	C=O at C2
Galactose	Hexose, Aldose	C₆H₁₂O₆	6	–CHO at C1
Mannose	Hexose, Aldose	C₆H₁₂O₆	6	–CHO at C1
Sedoheptulose	Heptose, Ketose	C₇H₁₄O₇	7	C=O

3.2 Structural Representations

D-Glucose — Open Chain (Fischer Projection)

Fischer Projection — D-Glucose (C₆H₁₂O₆)

D-Glucose — Haworth Projection (Pyranose Ring)

Haworth Projection — α-D-Glucopyranose

D-Fructose — Furanose Ring (Haworth)

β-D-Fructofuranose (5-membered ring)

HOCH₂ O CH₂OH \ | / C5 ——C4—C3 | \ OH C2 | OH (β: above ring) | C1H₂OH

D-Ribose — Open Chain

Fischer Projection — D-Ribose (C₅H₁₀O₅)

CHO ← C1 | H ———C———OH ← C2 | H ———C———OH ← C3 | H ———C———OH ← C4 | CH₂OH ← C5

3.3 Classification by Carbon Number

Carbon #	Name	Aldose Examples	Ketose Examples	Biological Role
3	Triose	Glyceraldehyde	Dihydroxyacetone	Glycolysis intermediates
4	Tetrose	Erythrose, Threose	Erythulose	Pentose phosphate pathway
5	Pentose	Ribose, Arabinose, Xylose	Ribulose, Xylulose	RNA/DNA backbone, ATP, NADH
6	Hexose	Glucose, Galactose, Mannose	Fructose	Primary energy source, glycogen, starch
7	Heptose	—	Sedoheptulose	Calvin cycle, pentose phosphate pathway

3.4 Aldoses vs. Ketoses

Aldoses

Aldehyde (–CHO) at C1
Reducing sugars (free aldehyde)
Examples: Glucose, Galactose, Mannose, Ribose
Undergo mutarotation
React with Fehling's / Benedict's reagents

Ketoses

Ketone (C=O) at C2
Weaker reducing properties
Examples: Fructose, Ribulose, Xylulose
Also undergo mutarotation in ring form
Form furanose (5-membered) rings preferentially

4 Isomerism

Isomers share identical molecular formulas but differ in structural arrangement or spatial orientation. Carbohydrate isomerism is fundamental to understanding biochemical specificity.

TYPES OF ISOMERISM IN CARBOHYDRATES

ISOMERS (same molecular formula)

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Structural Isomers

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Different functional groups
or connectivity
e.g. Glucose vs. Fructose

Stereoisomers

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Enantiomers

Mirror images
D-glucose / L-glucose

Diastereomers

Non-mirror; differ
at ≥1 chiral center
Glucose / Galactose

Anomers

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Differ at C1 only
α-glucose / β-glucose

Epimers

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Differ at one
specific C only
Glucose / Galactose (C4)

4.1 Structural Isomers

Structural Isomers: Glucose vs Fructose (Both C₆H₁₂O₆)

GLUCOSE (Aldohexose) FRUCTOSE (Ketohexose) ════════════════════ ═════════════════════ C1: CHO ← aldehyde C1: CH₂OH C2: H–C–OH C2: C=O ← ketone C3: HO–C–H C3: HO–C–H C4: H–C–OH C4: H–C–OH C5: H–C–OH C5: H–C–OH C6: CH₂OH C6: CH₂OH

4.2 Enantiomers: D- and L-Sugars

D-Glucose vs L-Glucose (Mirror Images)

D-Glucose L-Glucose ════════════ ════════════ CHO CHO | | H ——C—— OH HO ——C—— H | | HO ——C—— H H ——C—— OH | | H ——C—— OH HO ——C—— H | | H ——C—— OH ← C5 (ref) HO ——C—— H ← C5 (ref) | | CH₂OH CH₂OH OH on C5 = RIGHT (D) OH on C5 = LEFT (L) Naturally occurring ✓ Not naturally occurring ✗ Dextrorotatory (+112.2°) Levorotatory

4.3 Anomers (α and β)

📖 Anomers Explained

When the open-chain form cyclises, a new chiral centre forms at C1 (the anomeric carbon). The two forms are called α-anomer (OH at C1 is axial / below the ring) and β-anomer (OH at C1 is equatorial / above the ring). This interconversion in solution is called mutarotation.

Property	α-D-Glucose	β-D-Glucose
OH at C1	Below ring (axial)	Above ring (equatorial)
Specific rotation	+112.2°	+18.7°
Equilibrium in water	~36%	~64%
Stability	Less stable	More stable (equatorial OH)
Significance	Forms glycogen, starch (α-1,4)	Forms cellulose (β-1,4)

4.4 Optical Activity

Dextrorotatory (+): Rotates plane-polarized light to the right. Example: D-glucose (+52.7° at equilibrium)
Levorotatory (–): Rotates light to the left. Example: Fructose (–92°)
Racemic mixture: Equal amounts of (+) and (–) forms — optically inactive (net rotation = 0)
Invert sugar: Equimolar mixture of glucose and fructose produced by hydrolysis of sucrose; net levorotatory

5 Disaccharides

Two monosaccharide units linked by a glycosidic bond (formed via condensation — loss of H₂O). General formula: C₁₂H₂₂O₁₁.

5.1 Glycosidic Bond Formation

Condensation Reaction Monosaccharide₁–OH + HO–Monosaccharide₂ → Monosaccharide₁–O–Monosaccharide₂ + H₂O

5.2 Maltose (Malt Sugar)

Property	Details
Molecular formula	C₁₂H₂₂O₁₁
Composition	Glucose + Glucose
Glycosidic bond	α-1,4 (C1 of glucose₁ → C4 of glucose₂)
Reducing sugar?	Yes (free anomeric C1 on second glucose)
Enzyme for hydrolysis	Maltase (α-glucosidase)
Natural source	Germinating barley, starch hydrolysis

Chemical Equations — Maltose

Enzymatic Hydrolysis C₁₂H₂₂O₁₁ + H₂O →(Maltase)→ 2 C₆H₁₂O₆ (Glucose)

Fermentation to Ethanol C₁₂H₂₂O₁₁ + H₂O →(Yeast)→ 4 C₂H₅OH + 4 CO₂

Combustion C₁₂H₂₂O₁₁ + 12 O₂ → 12 CO₂ + 11 H₂O + ΔH

5.3 Lactose (Milk Sugar)

Property	Details
Molecular formula	C₁₂H₂₂O₁₁
Composition	Galactose + Glucose
Glycosidic bond	β-1,4 (C1 galactose → C4 glucose)
Reducing sugar?	Yes
Enzyme	Lactase (β-galactosidase)
Sweetness	~16% as sweet as sucrose

Hydrolysis of Lactose C₁₂H₂₂O₁₁ + H₂O →(Lactase)→ C₆H₁₂O₆ (Galactose) + C₆H₁₂O₆ (Glucose)

Hydrogenation Lactose + H₂ →(Ni catalyst)→ Lactitol (sugar alcohol — used in sugar-free products)

5.4 Sucrose (Table Sugar)

Property	Details
Molecular formula	C₁₂H₂₂O₁₁
Composition	α-Glucose + β-Fructose
Glycosidic bond	α-1,β-2 (C1 glucose → C2 fructose; both anomeric carbons linked)
Reducing sugar?	No — both anomeric carbons are involved in the bond
Enzyme	Sucrase (invertase)
Optical rotation	+66.5° (dextrorotatory)

Hydrolysis (Inversion) C₁₂H₂₂O₁₁ + H₂O →(Sucrase/acid)→ C₆H₁₂O₆ (Glucose, +52.7°) + C₆H₁₂O₆ (Fructose, –92°) Net rotation changes from +66.5° to ~–20° → called INVERT SUGAR

Complete Combustion C₁₂H₂₂O₁₁ + 12 O₂ → 12 CO₂ + 11 H₂O ΔG = –5644 kJ/mol

Dehydration (concentrated H₂SO₄) C₁₂H₂₂O₁₁ →(conc. H₂SO₄)→ 12 C + 11 H₂O (charring/blackening)

5.5 Reducing vs. Non-Reducing Sugars

Reducing Sugars

Free anomeric –OH (C1 in aldoses)
Reduce Benedict's, Fehling's, Tollens' reagents
Examples: Glucose, Fructose, Maltose, Lactose, Galactose
Undergo mutarotation in solution

Non-Reducing Sugars

Both anomeric carbons engaged in glycosidic bond
Cannot reduce oxidizing reagents
Examples: Sucrose, Trehalose
Do not show mutarotation

5.6 Isomaltose

An isomer of maltose with an α-1,6 glycosidic bond (C1 → C6). Also formula C₁₂H₂₂O₁₁. It is a reducing sugar and yields 2 glucose molecules upon hydrolysis. Found at branch points of glycogen/starch, produced by action of isomaltase.

6 Polysaccharides

Polymers of monosaccharide units (>10) joined by glycosidic bonds. General formula: (C₆H₁₀O₅)_n for hexose-based polysaccharides.

6.1 Starch

Property	Amylose	Amylopectin
% in starch	~20–30%	~70–80%
Structure	Unbranched, helical	Branched
Bond type	α-1,4 only	α-1,4 (chain) + α-1,6 (branch)
Branch frequency	None	Every 24–30 glucose units
Iodine test	Deep blue-black	Purple-reddish
Molecular mass	~200,000 Da	~200,000,000 Da

Hydrolysis of Starch (C₆H₁₀O₅)n + n H₂O →(amylase/acid)→ n C₆H₁₂O₆ (Glucose)

6.2 Glycogen ("Animal Starch")

Formula: (C₆H₁₀O₅)_n
Bonds: α-1,4 (linear) + α-1,6 (branches every 8–12 units — more branched than amylopectin)
Stored in liver (glucose homeostasis) and skeletal muscle (fuel for contraction)
Rapidly mobilized by glycogen phosphorylase → Glucose-1-phosphate → enters glycolysis

6.3 Cellulose

Formula: (C₆H₁₀O₅)_n — n up to 10,000–15,000
Bonds: β-1,4 glycosidic bonds between β-D-glucose units
Alternating glucose units are flipped 180°, enabling extensive hydrogen bonding → rigid, fibrous structure
Most abundant organic polymer on Earth (~50% of plant biomass)
Humans lack cellulase → not digestible → acts as dietary fiber

Cellulose β-1,4 Linkage vs Starch α-1,4 Linkage

STARCH (α-1,4) CELLULOSE (β-1,4) ══════════════ ══════════════════ Glucose → Glucose → Glucose ← Glucose → (same orientation) (alternating 180° flip) Forms coiled HELIX Forms flat, linear SHEETS Digestible by humans Indigestible — dietary fiber Energy storage Structural (cell walls) Iodine → deep blue Iodine → no colour change

6.4 Chitin

Formula: [C₈H₁₃O₅N]_n
Polymer of N-acetyl-D-glucosamine linked by β-1,4 bonds
Second most abundant polysaccharide on Earth
Found in: fungal cell walls, arthropod exoskeletons, mollusc shells
Medical use: wound dressings (biocompatible, biodegradable)

6.5 Summary Table — Polysaccharides

Polysaccharide	Monomer	Bond Type	Function	Location
Starch (amylose)	α-D-Glucose	α-1,4	Energy storage	Plants
Starch (amylopectin)	α-D-Glucose	α-1,4 + α-1,6	Energy storage	Plants
Glycogen	α-D-Glucose	α-1,4 + α-1,6	Energy storage	Animals (liver, muscle)
Cellulose	β-D-Glucose	β-1,4	Structural	Plant cell walls
Chitin	N-Acetylglucosamine	β-1,4	Structural	Fungi, arthropods
Hyaluronic acid	GlcUA + GlcNAc	β-1,4 / β-1,3	Connective tissue, lubrication	Synovial fluid, cartilage

7 Amino Sugars & Derivatives

Sugars in which a hydroxyl (–OH) group is replaced by an amino (–NH₂) group, often subsequently acetylated to form N-acetyl derivatives.

Amino Sugar	Parent Sugar	Formula	Biological Role
D-Glucosamine	Glucose	C₆H₁₃NO₅	Component of chitin, glycoproteins, cartilage
N-Acetylglucosamine (GlcNAc)	Glucose	C₈H₁₅NO₆	Chitin, peptidoglycan (bacterial wall), glycoproteins
D-Galactosamine	Galactose	C₆H₁₃NO₅	Cartilage (chondroitin sulfate), blood group antigens
D-Mannosamine	Mannose	C₆H₁₃NO₅	Glycoproteins, cell recognition
Muramic acid	GlcNAc	C₉H₁₇NO₇	Peptidoglycan of bacterial cell walls
Neuraminic acid (sialic acid)	Mannosamine	C₁₁H₁₉NO₉	Cell surface recognition, viral attachment

🔬 Clinical Note

Glucosamine sulfate supplements are widely used for osteoarthritis. It is a precursor to glycosaminoglycans (GAGs) — the main components of cartilage matrix. Clinical evidence suggests moderate benefit in reducing joint pain.

Structure of D-Glucosamine (Open Chain)

D-Glucosamine — Fischer Projection

8 Vitamin C as a Carbohydrate Derivative

Name: L-Ascorbic Acid
Formula: C₆H₈O₆ (a hexuronic acid lactone — derivative of L-gulonolactone)
Considered a monosaccharide derivative (hexose-derived lactone)
Humans lack the enzyme L-gulonolactone oxidase → cannot synthesize it → must obtain from diet

Reversible Oxidation (Antioxidant Action) L-Ascorbic Acid (C₆H₈O₆) ⇌ Dehydroascorbic Acid (C₆H₆O₆) + 2H⁺ + 2e⁻

Biological Functions

Cofactor for prolyl and lysyl hydroxylase → hydroxylation of proline & lysine in procollagen → collagen cross-linking & stability
Antioxidant: scavenges ROS (reactive oxygen species), regenerates vitamin E
Enhances non-haem iron absorption by reducing Fe³⁺ → Fe²⁺
Involved in norepinephrine synthesis and carnitine biosynthesis
Immunostimulant — promotes neutrophil function

⚠️ Deficiency — Scurvy

Without vitamin C, collagen synthesis fails → scurvy: bleeding gums, perifollicular hemorrhages, poor wound healing, corkscrew hairs, arthralgia, anemia. Daily requirement: 65–90 mg/day (adults); UL = 2000 mg/day.

9 Biological Importance & Metabolism

9.1 Glycolysis (Cytoplasm)

Breakdown of one glucose → 2 pyruvate. Occurs in all cells. Does NOT require oxygen.

Net Equation of Glycolysis C₆H₁₂O₆ + 2 ADP + 2 Pᵢ + 2 NAD⁺ → 2 C₃H₄O₃ (Pyruvate) + 2 ATP + 2 NADH + 2 H₂O

Net ATP yield from glycolysis alone: 2 ATP

9.2 Krebs Cycle (Mitochondrial Matrix)

Pyruvate (×2) → Acetyl-CoA → enters the TCA cycle.

Overall Equation per Glucose (TCA cycle ×2) 2 Acetyl-CoA + 6 H₂O + 2 ADP + 2 Pᵢ → 4 CO₂ + 2 ATP + 6 NADH + 2 FADH₂

9.3 Oxidative Phosphorylation & Total ATP Yield

Stage	NADH produced	FADH₂ produced	ATP (direct)	Approx. ATP total
Glycolysis	2	0	2	~7
Pyruvate → Acetyl-CoA	2	0	0	~5
Krebs Cycle (×2)	6	2	2	~22
Total per Glucose	10	2	4	~30–32 ATP

Complete Aerobic Oxidation of Glucose C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ~30–32 ATP ΔG° = –2870 kJ/mol

9.4 Structural Roles

Cellulose: Rigidity of plant cell walls; resists enzymatic digestion
Chitin: Exoskeleton of arthropods; fungal cell wall integrity
Glycosaminoglycans (GAGs): Hyaluronic acid, chondroitin sulfate → components of cartilage, synovial fluid, connective tissue
Peptidoglycan: Structural integrity of bacterial cell walls (target for penicillin)

9.5 Immunological & Cell Signaling Roles

Glycoproteins and glycolipids on cell surfaces constitute the glycocalyx — mediates cell-cell recognition
ABO blood group antigens are oligosaccharide chains on red blood cell surfaces
Lectins are carbohydrate-binding proteins involved in immune responses
Viral hemagglutinins bind sialic acid residues on host cell glycoproteins (e.g., influenza)
Toll-like receptors (TLRs) recognize LPS (lipopolysaccharide) — initiating innate immune responses

9.6 Brain & Nervous System

🧠 Key Fact

The brain accounts for ~20% of the body's glucose consumption. Neurons rely almost exclusively on glucose for ATP generation (cannot oxidize fatty acids efficiently). During prolonged fasting, the brain adapts to use ketone bodies as an alternative fuel.

9.7 Dietary Fiber

Insoluble fiber (cellulose, hemicellulose): Increases stool bulk, promotes peristalsis, prevents constipation and colorectal cancer
Soluble fiber (pectin, beta-glucan, inulin): Lowers LDL cholesterol, slows glucose absorption → improves glycemic control
Recommended intake: 25–38 g/day (adults)

10 Clinical Relevance

Diabetes Mellitus

Type 1: Autoimmune destruction of β-cells → no insulin → hyperglycemia
Type 2: Insulin resistance → relative insulin deficiency
Hyperglycemia → glycation of proteins (HbA1c used for diagnosis/monitoring)
Management: insulin, metformin, dietary carbohydrate restriction

Lactose Intolerance

Deficiency of intestinal lactase
Undigested lactose fermented by colonic bacteria → bloating, diarrhea, cramps
Management: lactase supplements, lactose-free dairy, fermented products (yogurt)

Glycogen Storage Diseases (GSDs)

Enzyme deficiencies in glycogen synthesis/breakdown
Type I (von Gierke): glucose-6-phosphatase deficiency → hypoglycemia, hepatomegaly
Type II (Pompe): lysosomal acid α-glucosidase deficiency → muscle weakness
Type V (McArdle): muscle phosphorylase deficiency → exercise intolerance

Scurvy

Vitamin C deficiency → impaired collagen hydroxylation
Symptoms: bleeding gums, petechiae, poor wound healing, perifollicular hemorrhage
Treatment: vitamin C supplementation (200–500 mg/day)

Condition	Carbohydrate Defect	Key Symptom	Treatment
Diabetes Mellitus	Impaired glucose uptake/regulation	Hyperglycemia, polyuria, polydipsia	Insulin, oral hypoglycemics
Lactose Intolerance	Lactase deficiency	Bloating, diarrhea after dairy	Lactase enzyme, avoidance
Galactosemia	Galactose-1-phosphate uridyltransferase deficiency	Liver failure, cataracts, intellectual disability	Galactose-free diet
Fructosuria	Fructokinase deficiency	Benign — fructose in urine	No treatment needed
Von Gierke Disease	Glucose-6-phosphatase deficiency	Severe hypoglycemia, hepatomegaly	Frequent cornstarch feeds
Scurvy	Vitamin C (ascorbic acid) deficiency	Bleeding gums, poor healing	Vitamin C supplementation

11 Sources of Carbohydrates

Category	Specific Sources	Primary Carbohydrate	Notes
Cereal Grains	Wheat, rice, maize, oats, barley	Starch (amylose + amylopectin)	Staple energy source globally
Root Vegetables	Potato, sweet potato, yam, cassava	Starch	High glycemic index when cooked
Legumes	Lentils, peas, beans, chickpeas	Starch + oligosaccharides (raffinose)	Also high in fiber and protein
Fruits	Banana, mango, grapes, dates	Fructose, glucose, sucrose	Simple sugars — rapid energy
Dairy	Milk, yogurt, cheese	Lactose	Yogurt has reduced lactose (fermented)
Refined Sugars	Table sugar, honey, HFCS, syrups	Sucrose, glucose, fructose	Empty calories — minimal nutrients
Industrial Fermentation	Corn starch hydrolysis, sugarcane	Glucose, ethanol	Used in biofuels, pharmaceuticals
Biotechnology	Microbial production (recombinant)	Cyclodextrins, xanthan gum	Food additives, drug delivery

12 Industrial & Medical Applications

12.1 Food Industry

Brewing & Distilling: Maltose from starch hydrolysis → fermented by yeast → ethanol + CO₂. Beer, whiskey, vodka.
Baking: Sucrose as sweetener; yeast ferments glucose → CO₂ for leavening
Confectionery: Invert sugar (glucose + fructose) prevents sucrose crystallization in chocolates, fondants
Sweeteners: High-fructose corn syrup (HFCS) — enzymatic isomerization of glucose → fructose; widely used in soft drinks

12.2 Pharmaceutical Industry

Lactose: Most widely used excipient (filler) in tablet manufacturing — chemically inert, good compressibility
Cellulose (microcrystalline): Tablet binder/disintegrant; also used in capsule shells (hydroxypropyl methylcellulose — HPMC)
Chitin & Chitosan: Biodegradable wound dressings, hemostatic agents, drug delivery nanoparticles
Dextran: Plasma volume expander in IV solutions; used in chromatography (Sephadex)
Heparin: Glycosaminoglycan anticoagulant (repeating units of GlcUA + GlcNAc-sulfate)
Hyaluronic acid: Injected into joints for osteoarthritis; dermal fillers in cosmetics

12.3 Biotechnology

Bioethanol: Cellulosic ethanol from agricultural waste (lignocellulosic biomass) — sustainable biofuel
Bioplastics: Polylactic acid (PLA) from fermented corn starch → biodegradable packaging
Cyclodextrins: Cyclic oligosaccharides used in drug delivery to improve solubility and stability of poorly soluble drugs
Xanthan gum / Guar gum: Microbial/plant polysaccharides used as food thickeners and in oil drilling fluids

12.4 Nutrition & Dietary Supplements

Glucosamine sulfate: OTC supplement for joint health / osteoarthritis
Inulin & FOS: Prebiotic dietary fibers → nourish beneficial gut bacteria
β-Glucan (oats): Lowers LDL cholesterol; FDA-approved health claim
Pectin: Soluble fiber; used as gelling agent in jams; cholesterol-lowering

13 Summary Tables & Revision Tools

Master Comparison Table

Compound	Formula	Type	Bond	Reducing?	Enzyme	Function
Glucose	C₆H₁₂O₆	Monosaccharide	—	Yes	Hexokinase	Energy, glycolysis
Fructose	C₆H₁₂O₆	Monosaccharide	—	Yes	Fructokinase	Energy, invert sugar
Galactose	C₆H₁₂O₆	Monosaccharide	—	Yes	Galactokinase	Lactose component, brain galactolipids
Ribose	C₅H₁₀O₅	Monosaccharide	—	Yes	—	RNA backbone, ATP, NADH
Maltose	C₁₂H₂₂O₁₁	Disaccharide	α-1,4	Yes	Maltase	Beer, baking
Lactose	C₁₂H₂₂O₁₁	Disaccharide	β-1,4	Yes	Lactase	Dairy, infant formula
Sucrose	C₁₂H₂₂O₁₁	Disaccharide	α-1,β-2	No	Sucrase	Table sugar, sweetener
Starch	(C₆H₁₀O₅)n	Polysaccharide	α-1,4 / α-1,6	No	Amylase	Plant energy store
Glycogen	(C₆H₁₀O₅)n	Polysaccharide	α-1,4 / α-1,6	No	Glycogen phosphorylase	Animal energy store
Cellulose	(C₆H₁₀O₅)n	Polysaccharide	β-1,4	No	Cellulase (absent in humans)	Plant cell wall, fiber
Chitin	[C₈H₁₃O₅N]n	Polysaccharide	β-1,4	No	Chitinase	Exoskeleton, fungal wall

Quick Revision: Key Chemical Equations

1. Aerobic Respiration (Complete) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 30–32 ATP 2. Anaerobic Fermentation (Yeast) C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂ (ΔG = –218 kJ/mol) 3. Sucrose Hydrolysis (Inversion) C₁₂H₂₂O₁₁ + H₂O →(sucrase/H⁺)→ C₆H₁₂O₆ + C₆H₁₂O₆ (glucose) (fructose) 4. Starch Hydrolysis (C₆H₁₀O₅)n + nH₂O →(amylase)→ nC₆H₁₂O₆ 5. Maltose Hydrolysis C₁₂H₂₂O₁₁ + H₂O →(maltase)→ 2 C₆H₁₂O₆ 6. Lactose Hydrolysis C₁₂H₂₂O₁₁ + H₂O →(lactase)→ C₆H₁₂O₆ + C₆H₁₂O₆ (glucose) (galactose) 7. Vitamin C Oxidation C₆H₈O₆ ⇌ C₆H₆O₆ + 2H⁺ + 2e⁻ (Ascorbate → Dehydroascorbate)

Memory Mnemonics

💡 Mnemonics for Exam

"All Good Men Love Fructose" → Aldoses: Glyceraldehyde, Mannose, Lactaldehyde, Fructose (structural isomer)
"SUcrose = Sugar, Unreduced" → Sucrose is a NON-reducing disaccharide
"β = Better for structure" → β-1,4 bonds in cellulose/chitin → structural rigidity
"α = Available for energy" → α-1,4 bonds in starch/glycogen → readily digestible energy stores
D sugars = OH at reference carbon on the RIGHT in Fischer projection
GLAD: Glycogen (Liver & muscle), Amylopectin (Dense branching), → both α-1,6 branches

Exam-Focused Quick-Fire Facts

Question	Answer
Most common monosaccharide in biology?	D-Glucose
Only non-reducing disaccharide listed?	Sucrose
Bond in cellulose vs starch?	β-1,4 (cellulose) vs α-1,4 (starch)
Energy yield per glucose (aerobic)?	~30–32 ATP
Vitamin C deficiency disease?	Scurvy
Milk sugar?	Lactose (Glucose + Galactose)
Animal storage polysaccharide?	Glycogen (liver & muscle)
Most abundant organic polymer on Earth?	Cellulose
Amino sugar in chitin?	N-Acetylglucosamine (GlcNAc)
Pentos found in RNA?	Ribose (C₅H₁₀O₅)
Enzyme that breaks starch?	Amylase (salivary & pancreatic)
What is mutarotation?	Interconversion of α and β anomers in solution until equilibrium
Glycemic index of pure glucose?	100 (reference standard)
What is invert sugar?	Equimolar mix of glucose + fructose from sucrose hydrolysis
Heparin chemical class?	Glycosaminoglycan (anticoagulant)