📋 Task:
Draw the Fisher (open-chain) and the Haworth (pyranose and furanose cycles) projections for the following carbohydrates. For the Haworth projections draw α- and β-anomers and name them.
a. D-Galactose
Fisher Projection (Open-chain)
IUPAC Name: (3R,4S,5R,6R)-6-(hydroxymethyl)oxane-2,3,4,5-tetrol
Common Name: D-Galactose
Anomers: α-D-galactopyranose (OH at C1 down), β-D-galactopyranose (OH at C1 up)
Structure: D-Galactose is an aldohexose, epimer of glucose at C4. In pyranose form, it forms a 6-membered ring.
b. D-Sorbose
Fisher Projection (Open-chain)
IUPAC Name: (3S,4R,5R)-1,3,4,5,6-Pentahydroxyhexan-2-one
Common Name: D-Sorbose
Anomers: α-D-sorbofuranose and β-D-sorbofuranose (5-membered ring)
Structure: D-Sorbose is a ketohexose. Predominantly forms furanose (5-membered) ring.
c. D-Xylose
Fisher Projection (Open-chain)
IUPAC Name: (2R,3R,4S)-5-(hydroxymethyl)oxane-2,3,4-triol
Common Name: D-Xylose
Anomers: α-D-xylopyranose and β-D-xylopyranose
Structure: D-Xylose is an aldopentose (5 carbons). Forms pyranose ring predominantly.
📋 Task:
Draw the structural fragment of homopolysaccharide cellulose. Name the monomers of cellulose. Name the glycosidic bond between monomers of cellulose. What is the biological importance of cellulose?
Cellulose Structure
Cellulose Fragment (2 units)
Structural Formula:
[β-D-Glcp-(1→4)-β-D-Glcp]n
Glycosidic Bond: β-1,4-glycosidic bond
Monomer: β-D-Glucose (β-D-glucopyranose)
Glycosidic Bond: β(1→4)-glycosidic linkage
Structure: Linear, unbranched polymer
Biological Importance:
- Structural component: Main component of plant cell walls
- Dietary fiber: Indigestible by humans, promotes digestive health
- Most abundant organic compound: On Earth
- Industrial uses: Paper, textiles, biofuels
- Provides rigidity: To plant structures
📋 Task:
Draw the structural fragment of homopolysaccharide glycogen. Name the monomers of glycogen. Name the glycosidic bonds between monomers of glycogen. What is the biological importance of glycogen?
Glycogen Structure
Glycogen Fragment (showing branching)
Main Chain: α-D-Glcp-(1→4)-α-D-Glcp
Branching: α-D-Glcp-(1→6)-α-D-Glcp (every 8-12 residues)
Monomer: α-D-Glucose (α-D-glucopyranose)
Glycosidic Bonds:
• α(1→4)-glycosidic bonds (linear chains)
• α(1→6)-glycosidic bonds (branch points, every 8-12 glucose units)
Structure: Highly branched polymer
Biological Importance:
- Energy storage: Main storage form of glucose in animals
- Located in: Liver and muscle tissues
- Rapid mobilization: Branched structure allows quick glucose release
- Blood glucose regulation: Liver glycogen maintains blood sugar
- Muscle energy: Muscle glycogen provides energy for contraction
📋 Task:
Draw the structural fragment of heteropolysaccharide chondroitin sulfate. Name the monomers of chondroitin sulfate. Name the glycosidic bonds between monomers of chondroitin sulfate. What is the biological importance of chondroitin sulfate?
Chondroitin Sulfate Structure
Chondroitin Sulfate Disaccharide Unit
Repeating Disaccharide:
[→4)-β-D-GlcA-(1→3)-β-D-GalNAc(4S)-(1→]n
Where:
GlcA = D-Glucuronic acid
GalNAc(4S) = N-Acetyl-D-galactosamine-4-sulfate
Monomers:
• D-Glucuronic acid (β-D-glucuronate)
• N-Acetyl-D-galactosamine-4-sulfate
Glycosidic Bonds:
• β(1→3) between GlcA and GalNAc
• β(1→4) between GalNAc and next GlcA
Biological Importance:
- Cartilage component: Major component of cartilage and connective tissue
- Joint health: Provides resistance to compression
- Medical use: Used as supplement for osteoarthritis
- Extracellular matrix: Important structural component
- Water retention: Sulfate groups bind water molecules
📋 Task:
Draw the structural fragment of heteropolysaccharide pectic acid. Name the monomers of pectic acid. Name the glycosidic bonds between monomers of pectic acid. What is the biological importance of pectic acid?
Pectic Acid Structure
Structure:
[→4)-α-D-GalA-(1→]n
Where:
GalA = D-Galacturonic acid (partially methylated)
Monomer: D-Galacturonic acid (α-D-galacturonate)
Glycosidic Bond: α(1→4)-glycosidic linkage
Note: Carboxyl groups partially methylated to form pectin
Biological Importance:
- Plant cell walls: Major component of primary cell walls
- Cell adhesion: Helps bind cells together
- Food industry: Gelling agent (jams, jellies)
- Dietary fiber: Soluble fiber, health benefits
- Fruit ripening: Breakdown causes fruit softening
📋 Task:
Draw the structural fragment of heteropolysaccharide chitin. Name the monomers of chitin. Name the glycosidic bonds between monomers of chitin. What is the biological importance of chitin?
Chitin Structure
Chitin Fragment (2 units)
Structural Formula:
[→4)-β-D-GlcNAc-(1→]n
Where:
GlcNAc = N-Acetyl-D-glucosamine
Monomer: N-Acetyl-D-glucosamine (β-D-GlcNAc)
Glycosidic Bond: β(1→4)-glycosidic linkage
Structure: Linear, unbranched polymer (similar to cellulose but with N-acetyl groups)
Biological Importance:
- Exoskeleton: Main component of arthropod exoskeletons (insects, crustaceans)
- Fungal cell walls: Structural component of fungi
- Second most abundant: Polysaccharide after cellulose
- Biomedical applications: Sutures, wound healing
- Biodegradable: Environmentally friendly material
📋 Task:
Draw the structural fragment of heteropolysaccharide hyaluronic acid. Name the monomers of hyaluronic acid. Name the glycosidic bonds between monomers of hyaluronic acid. What is the biological importance of hyaluronic acid?
Hyaluronic Acid Structure
Hyaluronic Acid Disaccharide Unit
Repeating Disaccharide:
[→4)-β-D-GlcA-(1→3)-β-D-GlcNAc-(1→]n
Where:
GlcA = D-Glucuronic acid
GlcNAc = N-Acetyl-D-glucosamine
Monomers:
• D-Glucuronic acid (β-D-glucuronate)
• N-Acetyl-D-glucosamine
Glycosidic Bonds:
• β(1→3) between GlcA and GlcNAc
• β(1→4) between GlcNAc and next GlcA
Biological Importance:
- Synovial fluid: Lubricates joints
- Skin hydration: Binds water, maintains skin elasticity
- Extracellular matrix: Important structural component
- Wound healing: Promotes tissue repair
- Cosmetic use: Anti-aging, dermal fillers
- Eye health: Component of vitreous humor
📋 Task:
Write down the reaction between α-D-glucopyranose and β-D-fructofuranose with α-1,2-glycosidic bond formation. Give common and IUPAC name of the product. What is the biological importance of the resulted compound?
Sucrose Formation Reaction
Reaction:
α-D-Glucopyranose + β-D-Fructofuranose → Sucrose + H₂O
Structural:
α-D-Glcp-(1→2)-β-D-Fruf
Common Name: Sucrose (table sugar)
IUPAC Name: β-D-Fructofuranosyl α-D-glucopyranoside
Glycosidic Bond: α,β(1→2)-glycosidic linkage
Note: Both anomeric carbons are involved (non-reducing sugar)
Biological Importance:
- Transport sugar: Main transport form in plants
- Energy source: Dietary carbohydrate
- Sweetener: Most common natural sweetener
- Food preservation: Used in jams, preserves
- Metabolism: Hydrolyzed to glucose + fructose
📋 Task:
Write down the reaction between β-D-galactopyranose and β-D-glucopyranose with β-1,4-glycosidic bond formation. Give common and IUPAC name of the product. What is the biological importance of the resulted compound?
Lactose Formation Reaction
Reaction:
β-D-Galactopyranose + β-D-Glucopyranose → Lactose + H₂O
Structural:
β-D-Galp-(1→4)-D-Glcp
Common Name: Lactose (milk sugar)
IUPAC Name: β-D-Galactopyranosyl-(1→4)-D-glucopyranose
Glycosidic Bond: β(1→4)-glycosidic linkage
Note: Reducing sugar (glucose anomeric carbon free)
Biological Importance:
- Milk sugar: Main carbohydrate in mammalian milk
- Infant nutrition: Energy source for newborns
- Calcium absorption: Enhances calcium uptake
- Lactose intolerance: Common enzyme deficiency (lactase)
- Food industry: Used in pharmaceuticals, baby food
📋 Task:
In human organism glucose metabolism (glycolysis) starts from phosphorylation reaction with ATP and hexokinase. Write down the reaction between α-D-glucopyranose and ATP with 6-phosphate-α,D-glucopyranose formation and explain its mechanism.
Glucose Phosphorylation Reaction
Reaction:
α-D-Glucopyranose + ATP → Glucose-6-phosphate + ADP + H⁺
Enzyme: Hexokinase (or Glucokinase in liver)
Cofactor: Mg²⁺ (required)
Product: Glucose-6-phosphate (G6P)
IUPAC Name: α-D-Glucopyranose 6-(dihydrogen phosphate)
Reaction Type: Phosphorylation (transfer of phosphate group)
Mechanism:
- Substrate binding: Glucose and ATP bind to hexokinase active site
- Mg²⁺ coordination: Mg²⁺ coordinates with ATP phosphate groups
- Nucleophilic attack: OH group at C6 of glucose attacks γ-phosphate of ATP
- Phosphate transfer: Phosphate transferred from ATP to C6-OH of glucose
- Product release: G6P and ADP released from enzyme
Biological Significance:
- First step of glycolysis: Commits glucose to metabolism
- Traps glucose: Phosphorylated glucose cannot leave cell
- Irreversible: Highly exergonic (ΔG°' = -16.7 kJ/mol)
- Regulatory step: Controlled by product inhibition (G6P)
- Requires Mg²⁺: Essential cofactor for ATP binding
📋 Task:
Phenols are poisons for human organism. Phenols detoxification in the body occurs in the result of carbohydrates alkylation. Write the reaction between D-galactopyranose and phenol and name the product.
Phenol Glycosylation (Detoxification)
Reaction:
β-D-Galactopyranose + Phenol → Phenyl-β-D-galactopyranoside + H₂O
Reaction Type: Glycosylation (O-glycosidic bond formation)
Enzyme: UDP-galactose:phenol galactosyltransferase
Phenyl-β-D-galactopyranoside
Product: Phenyl-β-D-galactopyranoside
IUPAC Name: Phenyl β-D-galactopyranoside
Glycosidic Bond: β-O-glycosidic bond (phenolic oxygen)
Detoxification Mechanism:
- Inactivation: Glycosylation makes phenol water-soluble
- Excretion: Glycosides easily excreted in urine
- Reduced toxicity: Phenolic OH group blocked
- Phase II metabolism: Conjugation reaction
- Protective: Prevents phenol from damaging proteins
📋 Task:
D-sorbitol is used as a sugar substitute for diabetics. In human organism D-sorbitol forms in the endothelial cells in the result of open-chain D-glucose reduction in the presence of NADH and aldose reductase enzyme. Write down this reaction.
D-Glucose Reduction to D-Sorbitol
Reaction:
D-Glucose (open-chain) + NADH + H⁺ → D-Sorbitol + NAD⁺
Enzyme: Aldose reductase
Cofactor: NADH (reducing agent)
Product: D-Sorbitol (D-Glucitol)
IUPAC Name: (2R,3R,4R,5S)-Hexane-1,2,3,4,5,6-hexol
Reaction Type: Reduction of aldehyde to primary alcohol
Change: Aldehyde group (C1) → Primary alcohol (CH₂OH)
Mechanism:
- Ring opening: D-Glucose opens to linear aldehyde form
- Hydride transfer: NADH donates hydride (H⁻) to carbonyl carbon (C1)
- Protonation: Carbonyl oxygen accepts proton (H⁺)
- Product formation: Aldehyde converted to primary alcohol
Biological & Medical Importance:
- Sugar substitute: Sweetener for diabetics (low glycemic index)
- Diabetic complication: Sorbitol accumulation in tissues causes damage
- Osmotic effect: Sorbitol draws water into cells
- Cataracts: Sorbitol in lens causes osmotic stress
- Neuropathy: Accumulation in nerves causes damage
- Food industry: Humectant, sweetener, texturizer
📋 Task:
In medicine, drugs with D-galacturonic acid are used as anti-inflammatory and antiviral agents. In human body D-galacturonic acid forms in the result of D-galactopyranose oxidation in the presence of oxidase enzyme. Write down this reaction.
D-Galactose Oxidation to D-Galacturonic Acid
Reaction:
D-Galactopyranose + O₂ + H₂O → D-Galacturonic acid + H₂O₂
Enzyme: Galactose oxidase (or Galactose dehydrogenase with NAD⁺)
Oxidizing agent: Molecular oxygen (O₂)
Product: D-Galacturonic acid
IUPAC Name: (2S,3R,4S,5R)-2,3,4,5-Tetrahydroxy-6-oxohexanoic acid
Reaction Type: Oxidation of primary alcohol to carboxylic acid
Change: CH₂OH group at C6 → COOH (carboxyl group)
Mechanism:
- Substrate binding: D-Galactose binds to oxidase active site
- Alcohol oxidation: Primary alcohol (C6) oxidized to aldehyde
- Further oxidation: Aldehyde oxidized to carboxylic acid
- Electron transfer: Electrons transferred to O₂, forming H₂O₂
Medical Applications:
- Anti-inflammatory: Used in anti-inflammatory drugs
- Antiviral: Exhibits antiviral activity
- Pectin component: Main monomer of pectic acid
- Detoxification: Conjugation with toxins
- Connective tissue: Component of glycosaminoglycans
- Pharmaceutical: Drug delivery systems
End of Topic 3 Solutions
All carbohydrate structures, reactions, and biological importance covered with molecular visualizations.