Biology 12

54 MHR • Unit 1 Metabolic Processes

Recent studies on synthetic oligosaccharides

(carbohydrates composed of a relatively small

number of monosaccharides) indicate they have

great potential as therapeutic agents. These

compounds, which interfere with carbohydrate–

protein reactions, are difficult to create in the

laboratory. However, a new technology has been

discovered using glycosidases, which are produced

by genetically altering DNA. These altered enzymes

catalyze the synthesis but not the hydrolysis of

oligosaccharides, making them easier and less

expensive to construct. The altered enzymes have

been termed glycosynthases and can be used to

make anti-ulcer agents, therapeutic drugs for

middle-ear infections, and infant formula additives,

to name a few. Dr. Stephen Withers, a scientist

at the University of British Columbia, and his

co-workers were the first to develop glycosynthases.

They continue to be in the forefront of developing

new ways to use these enzymes and their

substrates in industry and medicine. The

“Canadians in Biology” profile on the previous

page provides a more complete account of the work

accomplished by Dr. Withers and his team.

By lowering the activation energy needed by

cells to start metabolic reactions, enzymes allow

biological systems to undertake necessary processes

at the temperatures that exist inside the cell.

People have learned a great deal about enzymes

and taken them from such diverse sources as yeast

and organisms living in hydrothermal vents in

order to manufacture foods and pharmaceuticals.

The following section discusses another aspect of

enzyme function and metabolic reactions within

cells — coupled reactions and the production of ATP.

SECTION REVIEW

1. Define the term “catalysis.”


2. (a)Draw and label a diagram that shows the
   nature of the catalytic cycle.
   (b)How is the cyclic nature of this process energy-
   efficient for the cell?


3. What are the different ways that hydrolytic and
   oxidative enzymes change chemical reactions?


4. Make a three- to five-panel cartoon to show an
   example of a metabolic pathway. Explain the terms
   “substrate” and “product” as part of this cartoon.


5. Explain how the enzyme sucrase can participate
   in a reaction involving sucrose, but not in a reaction
   involving maltose. Use diagrams in your answer.


6. (a)Label the diagram with the following terms:
   substrates, enzyme, active site, product,
   enzyme–substrate complex.
   (b)How is enzyme shape important to the
   enzyme–substrate complex?
   7. Identify two ways in which enzymes reduce the
   activation energy necessary to break the bonds of
   the substrate.
   8. Make a chart that lists four factors that influence
   enzyme activity. For each factor, provide an example
   and a brief explanation of how the factor influences
   enzyme activity.
   9. Most enzymes function at a pH range of 6 to 8.
   What is one notable exception?


7. Describe how thermostable enzymes may be
   helpful to the pharmaceutical industry.


8. Use diagrams to show how non-competitive
   inhibitors act differently from competitive inhibitors.


9. Enzymes can be dissolved in the cytosol or
   embedded on a membrane. Identify one advantage
   and one disadvantage of each situation.


10. Pepsin is an enzyme that breaks down protein.
    (a)A student has a test tube that contains pepsin,
    egg white, and water. What conditions would
    you recommend to ensure breakdown of the
    egg white?
    (b)How could you increase the rate of the reaction?

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