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 MOLECULES OF LIFE

Carbohydrates (elements (CH2O)n)

Organization:

Monosaccharides

Disaccharides

Polysaccharides

Monosaccharides

5C pentoses (eg ribose, deoxyribose)
6C hexoses (eg glucose, fructose, galactose)

Glycoside linkage to form disaccharides

The two sugars are joined by condensation and may be broken by hydrolysis.

Different monosaccharides can be used:

sucrose = glucose + fructose
lactose = glucose + galactose
maltose = glucose + glucose

Polysaccharides: Common ones based upon glucose

Branched polysaccharides:
Amylose & amylopectin (starches) are synthesised in plants.
Glycogen is synthesised in animals. It is more highly branched than starches = more compact.
Unbranched polysaccharides:
Cellulose in plant cell walls.

FUNCTIONS OF THE CARBOHYDRATES

Sugars (mono and disaccharides) - small molecules, soluble in water:

  • maintenance of osmotic balance (e.g. salts in blood plasma, plant cell turgidity)
  • transport of energy reserves (e.g. glucose in blood or sucrose in sap)
  • energy substrate (respiration and photosynthesis)
  • energy store (sugar cane)
  • flavouring (fruits).
  • reward (nectar)
  • precursors (building blocks) of polysaccharides, nucleotides and amino acids.

Polysaccharides - large molecules, insoluble in water.

  • osmotically inactive carbohydrate storage (seeds, roots, chloroplasts)
  • structural (cellulose in plants)

© Paul Billiet 2008