What is a glycosidic bond?

The covalent C–O–C bond that joins two monosaccharides.

A reaction in which a molecule of water is added to break a bond.

What are the three monosaccharides in this topic?

Glucose, fructose and galactose (all C₆H₁₂O₆).

How are polysaccharides formed?

By many condensation reactions, forming a glycosidic bond each time.

How many glycosidic bonds are in an unbranched chain of 50 glucose units?

49 (one fewer than the number of units).

Why does hydrolysis of a chain give glucose of greater total mass?

Water molecules are added and become part of the glucose molecules.

Condensation, hydrolysis and glycosidic bondsEdexcel International A Level Biology: Flashcards

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What is a condensation reaction?

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What is a condensation reaction?: A reaction that joins two molecules by removing a molecule of water.
What is a glycosidic bond?: The covalent C–O–C bond that joins two monosaccharides.
What is hydrolysis?: A reaction in which a molecule of water is added to break a bond.
Which monosaccharides form maltose?: Glucose and glucose.
Which monosaccharides form sucrose?: Glucose and fructose.
Which monosaccharides form lactose?: Glucose and galactose.
What are the three monosaccharides in this topic?: Glucose, fructose and galactose (all C₆H₁₂O₆).
What is released when two monosaccharides join?: A molecule of water.
How are polysaccharides formed?: By many condensation reactions, forming a glycosidic bond each time.
Which enzyme hydrolyses lactose?: Lactase.
Which enzyme hydrolyses starch to maltose?: Amylase.
How many glycosidic bonds are in an unbranched chain of 50 glucose units?: 49 (one fewer than the number of units).
How many water molecules are needed to hydrolyse a disaccharide?: One.
Why does hydrolysis of a chain give glucose of greater total mass?: Water molecules are added and become part of the glucose molecules.

Exam questions on Condensation, hydrolysis and glycosidic bonds

Sucrose is the main sugar transported in the phloem of a sugar-cane plant. The plant makes sucrose in its leaves from two monosaccharides.
Describe how a molecule of sucrose is formed from its two monosaccharides.2 marks
Milk contains the disaccharide lactose. A man with lactose intolerance has too little of the enzyme lactase in his small intestine, so lactose in milk is not digested properly.
Explain how lactase breaks down lactose, referring to the bond and to water.2 marks
During germination, a barley seed releases amylase, which digests the starch stored in the seed. The embryo needs glucose for respiration. Starch is an unbranched polysaccharide in this example, made of glucose units joined by glycosidic bonds.
Explain how amylase and maltase together convert starch into glucose.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).