Question

Which of the following carbohydrates exist in both linear and cyclic forms?

• A. Monosaccharides
• B. Disaccharides
• C. Oligosaccharides
• D. Polysaccharides

Answer 1

The correct option is A Monosaccharides

Monosaccharides are the simplest sugars which cannot be hydrolysed further. Monosaccharides can be divided further based on the number of carbon atoms present into trioses (3C) which include glyceraldehyde (aldose) and dihydroxyacetone (ketose), tetroses (4C) which include erythrose (aldose) and erythrulose (ketose), pentoses (5C) which include ribose (aldose), deoxyribose and ribulose (ketose), hexoses (6C) which include glucose (aldose), fructose (ketose), galactose, etc. If the structure contains a -CHO (aldehyde) group, it is referred to as aldose sugar and if it contains >C=O (keto) group, it is referred to as ketose sugar. Hence the simplest carbohydrate pairs are glyceraldehyde (aldose) and dihydroxyacetone (ketose). Pentoses and hexoses exist in both linear (chain) and cyclic (ring) forms.

Disaccharides are made up of 2 monosaccharides which are joined together by a glycosidic bond.

Oligosaccharides are made up of a few monosaccharide units (3-10) which are joined together by glycosidic bonds.

Polysaccharides are made up of more than 10 monosaccharide units which are joined together by glycosidic bonds.