Complex Carbohydrates (College Board AP Biology)

Carbohydrates

• Carbohydrates are monomers of sugars
• Monosaccharidescan join together via dehydration synthesis reactions to form disaccharides
• A dehydration synthesis reaction is one in which 2 molecules join together via the formation of a new chemical bond, with a molecule of water being released in the process
• A new covalent bond forms between the 2 monosaccharides, holding the disaccharide together
• To calculate the chemical formula of a disaccharide, you add all the carbons, hydrogens and oxygens in both monomers then subtract 2 H and 1 O (for the water molecule lost)
• All carbohydrates have the generic formula (CH₂O)_n
• They derive their name from 'hydrates of carbon'

Diagram of the Formation of a Disaccharide from Two Monosaccharides

Two monosaccharide monomers join together by dehydration synthesis to form a disaccharide

Uses of Carbohydrates

• Carbohydrates have different functions in biology
  • Energy storage
    • Starch in plants
    • Glycogen in animals
  • Starch forms a large part of the energy intake in the diet of herbivores
• Structural uses
  • Cellulose in plant cell walls
  • Chitin in some animals eg, insects
    • Forms an exoskeleton
• Dietary fiber
  • Many structural carbohydrates (eg. cellulose) are largely indigestible and form a large part of the dietary fiber requirements in the animal diet
• The types of monomer and the nature of the covalent bonds between monomers give each carbohydrate different properties
• Some carbohydrates are formed from straight chains of monomers eg. amylose
• Other carbohydrates are highly branched e.g glycogen
  • Highly branched carbohydrates have more terminal monomers (at the ends of a chain)
  • This makes them quicker to be synthesized and broken down
  • Which is an advantage for an energy storage compound that needs to be built up/used quickly