Complex Carbohydrates (College Board AP® Biology)

Molecular Structure of Complex Carbohydrates

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