IBDP Biology: Carbohydrates

• C₆H₁₂O₆
• Hexose sugar.
• Monomer for starch, glycogen and cellulose.
• Exists normally as a stable ring.
• Carbon 1 combines with oxygen atom on carbon 5.
• Various isomers exist.
• Same molecular formula, different structural formula.
  • alpha- glucose
  • beta- glucose
  • Have opposite arrangement of O and OH on carbon 1.
• This has great significance when forming polysaccharides.

• Many sugars.
• Polymers
• Formed by condensation reactions.

• Variable numbers of monosaccharides.
• Branched or unbranched chains.
• May be folded.
• Insoluble due to size.
• Exert no osmotic influence.
• Do not diffuse easily.
• Split into disaccharides and monosaccharides by hydrolysis.

When it comes to IBDP Biology,

• Up to 50% of a cell wall.
• 10,000 β-glucose molecules (approx).
• Joined by β-1,4 glycosidic bonds.
• Long unbranched chains.
• Every other β-glucose is inverted.
• This makes the chains very straight.
• Chains run parallel.
• Hydrogen bonds link the chains together
• They form bundles called microfibrils.
• Groups of microfibrils form cellulose fibres.
• These criss-cross in cell walls.
• They do not stretch in either direction
• This gives it considerable stability.
• It is a valuable structural material.
• Difficult to digest.
• Few organisms possess cellulase.
• Uses – cellophane, paper, cotton.

• When it comes to IBDP Biology, starch is found in most parts of a plant in starch grains.
• Food reserve from excess glucose:
  • Short term in photosynthetic cells
  • Food supply in seeds for germination.
• Important food supply in animals.
• Made of α glucose.
• 2 constituent structures:
  • • Approx 20% of starch.
    • α 1,4 glycosidic bonds.
    • Spiral structure held together by hydrogen bonds.
  • • Approx 80& of starch.
    • α 1,4 and α 1,6 bonds.
    • Branched chains.
• Compact for storage.
• Many branched ends enable rapid hydrolysis to release sugars.
• Amylase digests starch

• When it comes to IBDP Biology, major polysaccharide storage material in animals and fungi.
• Stored mainly in muscles and liver.
• Exists in granules.
• Made of α glucose.
• α 1,6 glycosidic bonds& α 1,4 bonds.
• Similar in structure to amylopectin, though shorter chains -α 1,6 bonds are more frequent.
• Even more compact for storage.
• Rapid hydrolysis due to many enzyme attachment points.

This is the end of this topic

CLICK HERE TO LEARN MORE ABOUT OUR IBDP BIOLOGY COURSES