2.2.c Describe the formation of a glycosidic bond by condensation, with reference both to polysaccharides and to disaccharides, including sucrose.
2.2.d Describe the breakage of glycosidic bonds in polysaccharides and disaccharides by hydrolysis, with reference to the non-reducing sugar test.
- Monosaccharides are sugars
- Two main functions of monosaccharides include: source of energy in respiration and monosaccharides join together to build larger molecules (polysaccharides).
- Glucose is the most important monosaccharide for metabolism.
- When two monosaccharides join together, they form disaccharides.
- When many monosaccharides join together, they form polysaccharides.
- Examples of disaccharides include: maltose (glucose + glucose), sucrose (glucose + fructose) and lactose (glucose + galactose).
- Examples of polysaccharides include: glycogen, starch and cellulose.
FORMATION OF DISACCHARIDES AND POLYSACCHARIDES:
- Condensation occurs wherein hydroxyl groups (-OH groups) in the ring structures of the monosaccharides align next to each other, and a water molecule is created (i.e., 2 hydrogens and 1 oxygen are lost from the ring structure).
- The oxygen that is left forms a bridge with between the two monosaccharides - also known as a glycosidic bond.
- To create a polysaccharide, this process happens multiple times.
The above image shows the formation of disaccharides via condensation, and also demonstrates that hydrolysis separates disaccharides into two monosaccharides.
BREAKAGE OF DISACCHARIDES AND POLYSACCHARIDES:
- Breakage is when water is added back to the ring structure.
- As such, this process is the opposite of condensation, and is called ‘hydrolysis’
- Here, disaccharides and polysaccharides breakdown into monosaccharides.
- Hydrochloric acid can be used to break disaccharides down into two monosaccharides when testing for the presence of non-reducing sugars (e.g., sucrose).
⚠️🧠 For your GCE CIE Biology exam remember:Condensation joins molecules; hydrolysis splits molecules.
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References:
Jones, M., & Parkin, M. (2018). Cambridge International AS and A Level Biology. Cambridge: Cambridge University Press.