Form and hydrolyse glycosidic bonds
Condensation forms glycosidic bonds between sugars; hydrolysis breaks them using water.
AS Level; Cambridge International Biology 9700, 2028–2030. Original explanatory diagrams and examples support syllabus learning; written answers are self-checked and teacher review remains pending.
Before you begin
- Recognise that biological molecules are built from smaller molecules and that structure is related to function.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which reaction breaks a glycosidic bond by adding water?
What you will learn
- Describe glycosidic-bond formation by condensation in disaccharides and polysaccharides
- Describe glycosidic-bond breakage by hydrolysis
- Connect hydrolysis with testing for non-reducing sugars
Condensation joins sugar units
When two monosaccharides join, a condensation reaction forms a covalent glycosidic bond and removes a molecule of water. Sucrose is a disaccharide formed from glucose and fructose. Repeated condensation joins many monosaccharides to make a polysaccharide.
The bond name and reaction describe different ideas: glycosidic is the covalent link between sugar units, while condensation is the reaction that forms the link and releases water.
Hydrolysis breaks the link
Hydrolysis adds water to break a glycosidic bond. In the non-reducing sugar test, dilute acid and heat hydrolyse a non-reducing sugar such as sucrose into reducing monosaccharides. After cooling and neutralising, Benedict solution can detect the reducing products.
Comparing untreated and hydrolysed portions helps distinguish reducing sugar already present from reducing sugar produced by hydrolysis. Hydrolysis does not make sugar atoms disappear; it changes how the units are joined.
Pause and explain
What happens to water when a glycosidic bond forms by condensation?
Worked example
Sucrose is hydrolysed and then gives a positive Benedict result. Explain the bond change and test result.
Show the worked solution
- Hydrolysis adds water and breaks the glycosidic bond.
- Sucrose yields reducing monosaccharides.
- Benedict solution detects those products.
Answer Hydrolysis breaks the glycosidic bond in sucrose, adding water and releasing glucose and fructose. These are reducing sugars, so the hydrolysed sample can give a positive Benedict result after it has been neutralised.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain how a glycosidic bond forms between two monosaccharides.
Give me a hint
Include the reaction type and water.
Compare my reasoning
- The monosaccharides join by condensation.
- A covalent glycosidic bond forms and water is removed.
A condensation reaction joins two monosaccharides by forming a covalent glycosidic bond and removing a molecule of water.
Look for these in your work
- Condensation named
- Bond and water change stated
Describe what hydrolysis does to a polysaccharide.
Give me a hint
Explain the role of water.
Compare my reasoning
- Water is added at glycosidic bonds.
- The polymer is broken into shorter sugar units.
Hydrolysis adds water to glycosidic bonds and breaks them, so a polysaccharide is split into shorter carbohydrate units or monosaccharides.
Look for these in your work
- Water used
- Bond breakage and products stated
A sample is negative with Benedict solution before treatment and positive after acid hydrolysis. Explain the biochemical evidence.
Give me a hint
Link the change to reducing products.
Compare my reasoning
- Hydrolysis breaks glycosidic bonds.
- A non-reducing sugar can yield reducing monosaccharides.
The acid hydrolysed glycosidic bonds in a non-reducing sugar, producing reducing monosaccharides. The positive Benedict result after hydrolysis, compared with the negative untreated result, supports the presence of non-reducing sugar.
Look for these in your work
- Hydrolysis explained
- Before/after comparison interpreted
Common mistakes
- Saying condensation adds water
- Saying hydrolysis joins sugar monomers
- Forgetting acid neutralisation before Benedict solution
What can you explain now?
Which reaction breaks a glycosidic bond by adding water?
Compare with the explanation
Hydrolysis
Hydrolysis uses water to break a bond.
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Make it stick
How do condensation and hydrolysis have opposite effects on glycosidic bonds?
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