Enzyme actionAQA A-Level Biology: Mind map

Exam questions on Enzyme action

1. Catalase, found inside liver cells, catalyses the breakdown of hydrogen peroxide, a toxic by-product of metabolism, into water and oxygen. Trypsin is made by the pancreas and secreted into the small intestine, where it catalyses the hydrolysis of proteins to shorter polypeptides.
   Explain why trypsin does not catalyse the breakdown of hydrogen peroxide.2 marks
2. In 1894 Emil Fischer proposed that an enzyme and its substrate fit together like a lock and key. In 1958 Daniel Koshland proposed a modified model after it was found that some enzymes can act on substrates of slightly different shapes and that the shape of an enzyme can change when its substrate binds.
   Explain how the induced-fit model accounts for an enzyme lowering the activation energy of a reaction.2 marks
3. Lactase is an enzyme made by cells lining the small intestine. It is anchored in the cell surface membrane with its active site facing the gut lumen, where it hydrolyses the disaccharide lactose to glucose and galactose. Some adults make too little lactase, and can take a tablet containing lactase from a fungus with dairy foods.
   A mutation in a different person replaces one amino acid in the active site of lactase with an amino acid with a different R group. The enzyme no longer hydrolyses lactose. Explain why.3 marks