Cambridge O Level Biology · Syllabus 5090 · Biotechnology and Genetic Modification
Lactase
What is Lactase?
An enzyme that hydrolyses lactose, the sugar naturally present in milk, into the simpler sugars glucose and galactose. Milk treated with lactase therefore has a much reduced lactose content and is sold as lactose-free milk. It is suitable for many people with lactose intolerance, who do not produce enough lactase of their own to digest lactose properly. Lactose intolerance is not the same as an allergy to milk protein: removing the lactose does not remove the protein, so lactose-free milk does not help with a milk-protein allergy. The enzyme name ends in -ase and the sugar it acts on ends in -ose, which is the reliable way to keep the two words apart.
This definition is part of the Biotechnology and Genetic Modification chapter in Cambridge O Level Biology.
Lactase in context
Biotechnology is the use of living organisms, cells or enzymes to make useful products. Yeast respires anaerobically, converting glucose to ethanol and carbon dioxide: the carbon dioxide raises bread dough, and the ethanol is the product collected in ethanol manufacture. Bacteria are chosen for industrial production because they reproduce rapidly, can make complex molecules, contain plasmids that can receive selected genes, and raise fewer ethical concerns than using animals. They are grown in fermenters, in which temperature, pH, oxygen, nutrient supply and waste products are all controlled. Isolated enzymes do industrial jobs of their own — proteases and lipases in biological washing powders, pectinase in fruit juice, lactase in lactose-free milk. Genetic modification is changing an organism's genetic material by removing, changing or inserting individual genes; inserting the human insulin gene into bacterial DNA lets bacteria make human insulin, and inserting genes into crops can give herbicide resistance, insect-pest resistance or increased vitamin content — each with benefits and risks that have to be weighed rather than declared.
Common mistakes with Lactase
- “Lactose-free milk is suitable for anyone who reacts badly to milk.” Why wrong It addresses lactose only. A milk-protein allergy is a response to the protein, which is entirely unchanged by lactase. Say instead Lactase-treated milk is suitable for many people with lactose intolerance. It does not help with milk-protein allergy, because the protein is still present.
- “Lactase is the sugar in milk.” Why wrong One letter, two different kinds of molecule. The sentence has an enzyme being digested by a sugar. Say instead Lactose is the sugar; lactase is the enzyme that hydrolyses it into glucose and galactose.
Examiner tips on Lactase
- Give the products by name. “Lactase breaks down lactose” is one mark at best. “Lactase hydrolyses lactose into glucose and galactose” is a complete answer, and naming both products is the detail that separates it from a vague one.
Questions students ask about Lactase
What is biotechnology?
Biotechnology is the use of living organisms, cells or enzymes to make useful products or to carry out useful processes. It includes using yeast to make bread and ethanol, growing bacteria in industrial fermenters, and using isolated enzymes such as proteases, pectinase and lactase. Genetic modification is one technique used within biotechnology, not another name for it.
How is lactose-free milk made?
Milk is treated with the enzyme lactase, which hydrolyses lactose — the sugar in milk — into glucose and galactose. The lactose content of the product therefore falls sharply, making it suitable for many people with lactose intolerance.
Does lactose-free milk help with a milk allergy?
No. Lactose intolerance and milk-protein allergy are different conditions. Lactase acts only on the sugar; the protein in the milk is unchanged, so lactose-free milk does not help with an allergy to milk protein.