Biology, Eighth Edition (Raven)

Chapter 6: Energy and Metabolism

Feedback Inhibition of Biochemical Pathways

How do enzymes interact with substrates to cause chemical reactions? Enzymes function by catalyzing reactions. A catalyst changes the rate of a chemical reaction without being permanently altered by that reaction. Enzymes greatly increase the rate of chemical reactions. This increase in the rate of reactions is accomplished by changing the conformation of substrate molecules so that the areas of the molecules that are involved in the reaction are exposed and much more likely to come into contact with one another. Changes in conformation of substrate molecules reduce the activation energy of the reaction. The reaction is much more likely to occur for any individual molecule and the reaction proceeds at a much faster rate than it would without the presence of the catalyst enzyme.

View the animation below, then complete the quiz to test your knowledge of the concept.


In feedback inhibition, the inhibitor of the biochemical pathway is typically
A)the substrate of the enzyme inhibited.
B)the product of the enzyme inhibited.
C)a substance that is produced towards the middle of the biochemical pathway.
D)the final product of the biochemical pathway.
E)a product of another biochemical pathway.

What does the inhibitor bind to during feedback inhibition?
A)active site of the enzyme being inhibited
B)allosteric site of the enzyme being inhibited
C)both A and B
D)neither A nor B
E)either A or B, depending on the biochemical pathway

Consider the biochemical pathway used to synthesize the amino acid proline. A high increase in the level of proline will most likely lead to
A)a decrease in proline production.
B)a further increase in proline production.
C)no change in the rate of proline production.
D)increased breakdown of proline.
E)proline being converted to praline.

If the end product of a biochemical pathway becomes available in the environment, it is crucial for the cell to continue making the product.

A biochemical pathway consists of a specific sequence of enzyme-catalyzed reactions.
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