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Introduction to the lesson
Enzymes have a very specific mode of action. In this lesson you will learn about the two different hypotheses regarding enzymes' mode of action. As you read about these, it is important to think about how the structure of the enzyme determines its mode of action. Refer back to ch.2 to clarify your knowledge of protein structure and make sure you can correlate the structure of proteins with the mode of action of enzymes. This is not done in detail in the text book but is very important for really understanding enzymes. You will also see in this lesson how enzymes lower activation energy to make chemical reactions in the body possible. In the next lesson we will examine different factors which either speed up or slow down enzyme action.
Reading
Read the section “The best means of defence is attack” in your biology text book (p.54)
Thinking it through
- What strikes you as amazing about this beetle’s means of defence?
- How effective do you think it is?
- Did you notice the names of the two enzymes mentioned? Most enzymes are names with “ase” at the end of the name
- What role do these two enzymes play?
- What do you think a catalyst is?
Mode of action of enzymes
Read the section under the title “Mode of action of enzymes” in your text book (p.54-57).
Learning Activity 1
Answer the following questions in your exercise book.
- What is the main function of enzymes?
- What is the difference between intracellular and extracellular enzymes?
- Enzymes are "globular" proteins.
- What level of structure is this?
- From what you learned in ch.2, are globular proteins soluble or insoluble in water and how does their structure make them this way? What is the significance of this in terms of enzymes' function? (Think specifically about the need for enzymes to get from one place to another in the body.)
- The active site of an enzyme needs to be a very specific shape. From your knowledge from ch.2, explain in detail what would be the effect on the enzyme's active site if only one amino acid was coded incorrectly in the amino acid chain/primary structure (include an explanation of what would happen to the secondary, tertiary and quarternary structure and what would be the effect when the deformed enzyme comes into contact with its substrate).
- What is the difference between the "lock and key" hypothesis and the "induced fit" hypothesis?
- Draw an annotated diagram of the interaction between an enzyme and its substrate (cf. Fig. 3.3 on p.55 of your textbook). Make sure you understand this process.
- Activation energy for chemical reactions is often very high (think about how hot you need to heat water to get sugar to dissolve in it). What would happen to the body if metabolic reactions had to take place at these temperatures?
- Copy Fig. 3.6 (p.57 of your textbook). Underneath your graph, give a detailed explanation for why the curve is steep at first but after a few seconds becomes more gradual.
Definitions and review:
Definitions
- Enzyme
- Catalyst
- Intracellular enzyme
- Extracellular enzyme
- Active site
- Lock and key hypothesis
- Enzyme-substrate complex
- Induced fit hypothesis
- Enzyme-product complex
- Activation energy
- Initial rate of reaction
Mindmap
Start a new mindmap for chapter three and add this section to it.