Practice Questions
Define the terms monosaccharide and polysaccharide. (2 marks)
Monosaccharide: a simple sugar / single carbohydrate monomer (1)
Polysaccharide: a complex carbohydrate polymer made of many monosaccharides bonded together (1)
Explain how monosaccharides can be joined to form a polysaccharide, and state two reasons why organisms build polysaccharides rather than keeping sugars only as monosaccharides. (6 marks)
Monosaccharides act as monomers that join to form larger carbohydrates (1)
Monosaccharides bond by forming covalent glycosidic linkages (1)
Linkage formation occurs via a condensation reaction producing water (1)
Any two of:
Polysaccharides allow energy to be stored in a compact form (1)
Polymers reduce osmotic effects compared with many free monosaccharides (1)
Polysaccharides can provide structural materials due to repeating linked units (1)
FAQ
In cells, many monosaccharides are predominantly in ring forms in aqueous solution, but they can interconvert between ring and open-chain forms.
Enzymes can still catalyse glycosidic bond formation because the relevant hydroxyl groups are available on the ring structure.
A reducing sugar has a free anomeric carbon that can participate in reactions that reduce other compounds.
When a glycosidic bond uses the anomeric carbon, that end may no longer be reducing; whether a polysaccharide has reducing ends depends on how its linkages are arranged.
Cells use specific enzymes that position monosaccharides and catalyse bond formation at particular carbon atoms and orientations.
This enzyme specificity ensures the same monomers can be assembled into different polysaccharides with distinct shapes and functions.
They refer to the carbon atoms on each monosaccharide that are connected by the glycosidic bond.
For example, “1–4” indicates a bond between carbon 1 of one sugar and carbon 4 of the next, which strongly influences the polymer’s geometry.
Yes. Some polysaccharides can be heteropolymers, built from more than one type of monosaccharide.
The sequence of monomers and the linkage types together determine the polymer’s chemical properties and how it interacts with water and proteins.
