Comparison of Polysaccharides:

(a) Monomer Composition:

All three are polymers of glucose (C₆H₁₂O₆)

• Starch: α-glucose
• Glycogen: α-glucose
• Cellulose: β-glucose

(b) Glycosidic Linkages:

Starch:

• Amylose: α-1,4 glycosidic bonds (unbranched)
• Amylopectin: α-1,4 bonds with α-1,6 branches every 24-30 glucose units

Glycogen:

• α-1,4 bonds with α-1,6 branches every 8-12 glucose units (highly branched)

Cellulose:

• β-1,4 glycosidic bonds (linear, unbranched)

(c) Structure:

Starch: Helical coils (amylose) and branched structure (amylopectin)

Glycogen: Highly branched, compact globular structure

Cellulose: Long, straight, unbranched chains that form hydrogen bonds with adjacent chains → microfibrils

(d) Biological Function:

Starch:

• Energy storage in plants
• Found in roots, tubers, seeds
• Easily digestible by amylase enzymes

Glycogen:

• Energy storage in animals
• Stored in liver and muscle cells
• Highly branched for rapid glucose release

Cellulose:

• Structural support in plant cell walls
• Provides rigidity and strength
• Most humans cannot digest (lack cellulase enzyme)
• Dietary fiber in human nutrition

$\boxed{\text{Storage: starch/glycogen (α-glucose); Structural: cellulose (β-glucose)}}$

Dehydration Synthesis (Condensation Reaction):

Formation of sucrose from glucose + fructose

Reactants:

• Glucose: C₆H₁₂O₆ (α-glucose, 6-carbon aldose)
• Fructose: C₆H₁₂O₆ (β-fructose, 6-carbon ketose)

Process:

1. Hydroxyl groups (-OH) from each monosaccharide approach

   • OH from C1 of glucose
   • OH from C2 of fructose

2. Dehydration occurs:

   • One monosaccharide loses H
   • Other monosaccharide loses OH
   • These combine to form H₂O (water)

3. Bond formation:

   • Oxygen links the two monosaccharides
   • Forms glycosidic bond (C-O-C)
   • Specifically: α-1,2 glycosidic linkage

Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + \text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{enzyme}} \text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O}$

$\text{Glucose} + \text{Fructose} \rightarrow \text{Sucrose} + \text{Water}$

Key Features:

• Anabolic reaction (builds larger molecules)
• Endergonic (requires energy input, usually ATP)
• Enzyme-catalyzed (sucrase in reverse, or sucrose synthase)
• Reversible via hydrolysis

Bond Formed: $\boxed{\text{Glycosidic bond (α-1,2 linkage)}}$

Reverse Reaction (Hydrolysis): Adding water breaks the glycosidic bond, releasing glucose and fructose. This is how we digest disaccharides.

Note: Sucrose is "table sugar" - the primary transport sugar in plants (phloem sap).