Carbohydrates- monosaccharides

Monosaccharides:

The smallest units (monomers) of carbohydrates are simple sugars and include trioses, pentoses and hexoses, named due to the number of carbon atoms present- they are monosaccharides.

• Monosaccharides are soluble in water, are sweet tasting and form crystals.
• The most common monosaccharide are hexose sugars
• Pentose and hexose sugars tend to form ring structures.

General formula:

(CH2O)n where n is a number between 3 and 9. They are classified according to the number of carbon atoms. The monosaccharides you will have to know fall into these categories:

C = 3 = triose

C = 4 = tetrose

C = 5 = pentose

C = 6 = hexose

Trioses: (e.g. glyceraldehydes), intermediates in respiration and photosynthesis.

Tetroses: rare.

Pentoses: (e.g. ribose, ribulose), used in the synthesis of nucleic acids (RNA and DNA), co-enzymes (NAD, NADP, FAD) and ATP.

Hexoses: (e.g. glucose, fructose), used as a source of energy in respiration and as building blocks for larger molecules.

All but one carbon atom have an alcohol (OH) group attached. The remaining carbon atom has an aldehyde or ketone group attached.

When Glucose forms a ring structure, it can do so in two different ways:

• If the OH at C1 is below the plane of the ring, it is called an α Glucose.
• If the OH at C1 is above the plane of the ring, it is called β Glucose.
• This difference in structure leads to a difference in properties.