|Stephen G. Saupe - Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; (320) 363-2782; firstname.lastname@example.org|
: Our two characters, Gink and Go, are sitting in the coffee shop discussing their favorite class, Concepts of Biology:
|Go:||I thought it was really interesting when Saupe told us today that the Mad Hatter in Lewis Carroll's book, Alice's Adventure's in Wonderland, was having enzyme problems.|
|Gink:||I always have enzyme problems. Do you mean that some of the enzymes of his nervous system weren't functioning properly?|
|Go:||Exactly. That's because mercury, which was used in the felting process of making hats, is a non-competitive inhibitor of enzymes.|
|Gink:||Is mercury binding to the active site of the enzyme?|
|Go:||Nope - you're thinking of a competitive inhibitor. Non-competitive inhibitors like mercury bind to a place on the enzyme other than the active site.|
|Gink:||Does the shape of the enzyme change when the inhibitor binds to it?|
|Go:||Of course. Mercury for example, breaks disulfide bonds that hold the enzymes in their 3-D shape.|
|Go:||Disulfide. Disulfide bonds, which are a type of covalent bond, join two sulfur atoms.|
|Gink:||It's all coming back - I hate that chemistry stuff. And cats, too. Got any mercury?|
|Go:||Now Gink .be serious (shake your finger vigorously at Gink).|
|Gink:||Okay .does any mercury bind to allosteric sites?|
|Go:||What are they?|
|Gink:||See smarty - I'm not so dumb (shake your finger vigorously at Go). Allosteric sites are regions of the enzyme, other than the active site, to which various regulator molecules can bind. When the allosteric regulators bind to these sites it changes the enzyme activity.|
|Go:||How could I have forgotten? I remember now that allosteric sites are an important way that enzyme activity can be regulated by the cell. Feedback inhibition is often involved. And, the process is reversible, unlike binding by mercury.|
|Gink:||I read that Newton went "mad" for awhile during his career. Was he poisoned by mercury, too?|
|Go:||You bet. And, there are many other examples. For example, you may have heard about the high frequency of birth defects in the Japanese fishing village of Minimata.|
|Gink:||I saw the photos by W. Eugene Smith and they were very sad. I sure hope that competitive and non-competitive inhibitors stay away from my enzymes.|
|Go:||Me too. You can't afford to be inhibited any more than you already are.|
Questions: After completing the dialog, answer the following questions:
1. Identify 3 ways that enzymes are held in their 3-D shape.
2. An enzyme/protein in its functional, 3-D shape is said to be in its
a. natural d. nurtured
b. native e. original
3. A protein/enzyme that has lost its typical 3-D shape is called _____________.
a. unnatural d. devastated
b. re-native e. atypical
4. Identify 3 conditions that might cause an enzyme to change its typical shape.
5. Compare and contrast active site and allosteric site.
How are they similar? How do they differ?
6. Inhibitors slow the rate of enzymatic reactions. Identify two mechanisms by which inhibitors can affect reaction rate.
7. Compare and contrast competitive and non-competitive
inhibitors. How are they similar? How do they differ?
8. Which type of inhibitor is mercury?
9. The St. Cloud Times recently (Sept '04) reported that a large quantity of mercury was found in the parking lots of a school. Explain why this was such a concern.
10. Defend or attack the statement: Mercury is a feedback inhibitor.
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Last updated: September 30, 2004
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