Glycosidic bonds: condensation and hydrolysis

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Glycosidic bonds: condensation and hydrolysisSpec 1.4

In short

A condensation reaction joins two monosaccharides by forming a glycosidic bond and releasing one molecule of water. Repeating it builds disaccharides (maltose, sucrose, lactose) and polysaccharides (glycogen, amylose, amylopectin). A hydrolysis reaction adds water to break a glycosidic bond and release the monosaccharides again.

In a condensation reaction, an –OH group on one monosaccharide and an –H on another are removed. They form a molecule of water, and the two sugars are joined by a C–O–C link called a glycosidic bond. In starch and glycogen the main chain is held together by α-1,4 glycosidic bonds (between carbon 1 of one glucose and carbon 4 of the next). Branches are made by α-1,6 glycosidic bonds.

glucose + glucose → maltose + water (C₆H₁₂O₆ + C₆H₁₂O₆ → C₁₂H₂₂O₁₁ + H₂O)

Two α-glucose molecules with carbons numbered 1 to 6; the –OH on carbon 1 of one and the H of the –OH on carbon 4 of the other are removed as water to form maltose with an α-1,4 glycosidic bond; hydrolysis adds water to reverse it. — Condensation forms an α-1,4 glycosidic bond and releases water; hydrolysis uses water to break it.

The disaccharides you need to know
Disaccharide	Made from	Found in
Maltose	Glucose + glucose	Germinating seeds; produced when starch is digested
Sucrose	Glucose + fructose	Sugar cane, sugar beet; the main sugar transported in phloem
Lactose	Glucose + galactose	Milk

A polysaccharide is made by repeating condensation many times. A chain of n monosaccharides contains n − 1 glycosidic bonds along the main chain, and n − 1 molecules of water are released when it forms.

Hydrolysis is the reverse reaction. A molecule of water is added across the glycosidic bond, which breaks it and releases the monosaccharides. In living organisms the reaction is catalysed by enzymes, for example amylase on starch and lactase on lactose.

Exam tip:

Name the reaction and the bond, and say what happens to water. Condensation forms a glycosidic bond and releases water. Hydrolysis uses water to break the bond.

Written and checked against the Edexcel International AS Level Biology (XBI11) specification · Updated October 2026

Frequently asked questions

Why is water a good solvent?

Water is a good solvent because its molecules are dipoles, with a slightly negative oxygen end and slightly positive hydrogen ends. These charged ends are attracted to ions and polar molecules, surround them and keep them apart, so they dissolve. This lets blood plasma and sap carry substances.

What is the difference between starch and glycogen?

Both are polysaccharides made of α-glucose, but starch is the energy store in plants and glycogen is the store in animals. Glycogen is more highly branched, with α-1,6 branches every 8 to 12 units, so it has more free ends and releases glucose faster.

What is a condensation reaction?

A condensation reaction joins two molecules together and releases a molecule of water. When monosaccharides join, a glycosidic bond forms. When glycerol and fatty acids join, ester bonds form. Hydrolysis is the reverse, as water is added to break the bond.

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