They are sugars. They dissolve easily in water to form sweet-tasing solutions. This is because they contain a lot of -OH groups, which are polar (hydrophilc).

EXTRA: The chemistry of monosaccharides

Monosaccharides contain a carbonyl group. Depending on the carbonyl group they contain they are classified as:

  • Aldoses when they contain an aldehyde. The suffix –ose is used in naming carbohydrates (E.g. pentose)
  • Ketoses when they contain a ketone. The suffix –ulose is used in naming carbohydrates (E.g. pentulose)

When they are added to water, monosaccharides tend to form cyclic structures which are more stable. These structures have two stereoisomers (also called anomers).

Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution), but that differ only in the three-dimensional orientations of their atoms in space (Wikipedia).

  • Alpha (α) stereoisomers: The -OH group on the first Carbon atom is drawn below the cycle
  • Beta (β) stereoisomers: The -OH group on the first Carbon atom is drawn above the cycle.

General formula: (CH2O)n

They consist of a single sugar molecule.


  • Source of energy in respiration (Due to large nr. of C-H bonds. When broken they release lots of energy which helps in making ATP, from ADP and phosphate.
  • Important building blocks for larger molecules (polysaccharides). For instance deoxyribose is used in making DNA, and ribose is used in making RNA.

Common monosaccharides are Glucose (C6H12O6), Fructose, Galactose, Ribose and Deoxyribose.

Glucose: Is the main source of energy in all organisms. It is used as a fuel to make ATP in aerobic respiration. Furthermore, it is the monosaccharide which is the most abundant as polymers (so it is used to make polymers – more molecules of the same type bond together). Humans normally contains about 80 mg of glucose per 100 cubic cm of blood.


One important aspect of pentoses (Contain 5 C atoms) and hexoses (Contain 6 C atoms) is that the chain of C atoms is long enough to close up, forming a more stable ring structure.

In glucose, the hydroxyl group (-OH) on the first C atom may be above or below the plane of the ring. If the OH is below the ring, the molecule is known as Alpha-Glucose. If the OH is above the ring, the molecule is known as Beta-Glucose.





1.1.2 Disaccharides

1.1.3 Polysaccharides

1.1.4 Practicals

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