1. KEY CONCEPT Enzymes are catalysts for chemical reactions in living things.
Like other carnivores, the Venus flytrap eats animals to get nutrients that it needs to make molecules such as proteins and nucleic acids. Other chemical compounds made by the plant's cells enable the Venus flytrap to digest the animals that it eats.

2. A catalyst lowers activation energy.
Catalysts are substances that speed up chemical reactions.
decrease activation energy
increase reaction rate

3. Enzymes allow chemical reactions to occur under tightly controlled conditions.
Enzymes are catalysts in living things.
Enzymes are needed for almost all processes.
Most enzymes are proteins.
Fig. This micrograph shows a pathogen after it has been captured. Once inside a white blood cell, enzymes are used to destroy the pathogen. (colored TEM; magnification 11,000 X)

4. Disruptions in homeostasis can prevent enzymes from functioning.
Enzymes function best in a small range of conditions.
Changes in concentrations, temperature and pH can break hydrogen bonds causing enzymes not to work properly.

5. Critical Viewing: Do you think a high-carbohydrate or a high protein meal would be digested more quickly? Explain.

6. An enzyme’s function depends on its structure.
An enzyme’s structure allows only certain reactants to bind to the enzyme.
An enzyme’s function depends on its structure.
substrates
active site
substrates (reactants)
enzyme
Substrates bind to an enzyme at certain places called active sites.

7. The lock-and-key model (inducible fit model) helps illustrate how enzymes function.
substrates brought together
bonds in substrates weakened
Substrates bind to an enzyme at certain places called active sites.
The enzyme brings substrates together and weakens their bonds.
The catalyzed reaction forms a product that is released from the enzyme. 1. 2. 3.
Apply: How does the structure of an enzyme affect its function?