Sciences - Co-ordinated (Double) - 0654 CIE

Enzymes

Overview

Inside every cell, thousands of chemical reactions must happen fast enough to keep you alive, yet at a gentle 37 degrees Celsius. The molecules that make this possible are enzymes: biological catalysts that speed reactions up enormously without being used up. One enzyme, catalase, can break down 40000 molecules every second.

In this lesson you will learn what enzymes are, how their active site fits a specific substrate like a lock and key, and how temperature and pH change their activity, including the irreversible damage of denaturation. At Extended level you will explain these effects in terms of shape, fit and collisions.

Objectives

Describe a catalyst as a substance that increases the rate of a chemical reaction and is not changed by the reaction
Describe enzymes as proteins that are involved in all metabolic reactions, where they function as biological catalysts
Describe why enzymes are important in all living organisms in terms of a reaction rate necessary to sustain life
Describe enzyme action with reference to the shape of the active site of an enzyme being complementary to its substrate and the formation of products
Investigate and describe the effect of changes in temperature and pH on enzyme activity with reference to optimum temperature and denaturation
[Supplement] Explain enzyme action with reference to: active site, enzyme-substrate complex, substrate and product
[Supplement] Explain the specificity of enzymes in terms of the complementary shape and fit of the active site with the substrate
[Supplement] Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy, shape and fit, frequency of effective collisions and denaturation
[Supplement] Explain the effect of changes in pH on enzyme activity in terms of shape and fit and denaturation

Lesson Note

Enzymes control every metabolic reaction, so they connect digestion, respiration, photosynthesis and more. Examiners reliably ask you to describe enzyme action with the lock-and-key idea and to explain the temperature and pH graphs, including denaturation. This is one of the highest-value topics in the whole course.

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Lesson Evaluation

Congratulations on completing the lesson on Enzymes. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

An enzyme is best described as a: A. carbohydrate catalyst B. protein that acts as a biological catalyst C. fat that speeds reactions D. mineral ion Answer: B
The part of an enzyme that binds the substrate is the: A. cell wall B. active site C. ribosome D. nucleus Answer: B
Above its optimum temperature an enzyme is: A. activated B. denatured C. dissolved D. used up Answer: B
An enzyme acts on only one type of substrate because: A. it is used up B. its active site has a complementary shape to that substrate C. it raises the temperature D. it is an acid Answer: B
Which statement about a catalyst is correct? A. it is used up in the reaction B. it slows reactions down C. it is not changed by the reaction D. it only works once Answer: C