B1.1 Polysaccharides
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What is a polysaccharide?
Polymer of monosaccharides via condensation reactions; composition and isomerization affect function.
Describe starch.
• α-glucose polymer • Amylose: unbranched, α-1,4 links • Amylopectin: branched, α-1,4 + α-1,6 links • Energy storage in plants, stored in amyloplasts, hydrolyzed to glucose.
Describe glycogen.
• α-glucose polymer, highly branched (α-1,4 + α-1,6 links) • Energy storage in animals (liver & muscle) • Rapid glucose release via enzymatic hydrolysis • More soluble than starch due to higher branching.
Describe cellulose.
• β-glucose polymer, unbranched, β-1,4 links • Chains form microfibrils via hydrogen bonds • Provides structural support in plant cell walls • Few organisms digest β-linkages.
How do polysaccharide structures relate to function?
• Branching → rapid glucose release (starch, glycogen) • Linear + hydrogen bonding → structural strength (cellulose) • Insolubility → storage/structure.
How is energy stored in polysaccharides mobilized?
By enzymatic hydrolysis into monosaccharides (e.g., starch → glucose).
Why are polysaccharides a good energy source?
Long chains allow high energy density release; branching increases rate of glucose availability.
Compare starch, glycogen, and cellulose.
Starch: plant energy storage, partly branched, α-glucose Glycogen: animal energy storage, highly branched, α-glucose Cellulose: structural, linear β-glucose, hydrogen-bonded microfibrils
Why do germinating seeds contain maltose?
Starch is broken down to mobilize glucose for energy during growth