Self Quiz on Metabolism -1
Come up with an answer FIRST, then "select" the line with the "*" to see the answer. If you just print this out or just look at the answers without thinking first, it won't do you a damn bit of good!

1. A bacterium uses methane gas as its carbon and energy source. What term would we use to describe this bacterium?

*    Chemoheterotroph or chemoorganotroph both work. Heterotroph only means that the methane is used for carbon, but not necessarily that is used for energy. Methane, CH4, is an organic molecule.

2. A bacterium oxidizes sulfur found in minerals to obtain energy and uses carbon dioxide as its carbon source. How do we classify it?

*    Chemoautotroph (or chemolithotroph).

3. What's a better source of energy for a bacterium, glycerol or methanol?

*    The 3 carbons of glycerol come out to -1, 0, and -1 for a total of -2.  The carbon in methanol also has a value of -2, so they turn out to be the same! Trick question, I guess.

4. What is an enzyme cofactor? What are some examples of organic cofactors?

*    A cofactor is a small molecule that helps in an enzyme reaction. Like the enzyme, it is not used up in the reaction. Examples we have covered in class:  NAD and Coenzyme A. Many "vitamins" are either cofactors or are used to make cofactors (the nicotinamide in NAD comes from a B vitamin).

5. What are three major differences between competitive inhibition and allosteric inhibition?

*    a) They take place at different sites on the enzyme, the active site and allosteric site, respectively
        b) Allosteric inhibitors are used by organisms to control the rate at which chemical reactions occur and to            regulate pathways; competitive inhibition is caused by harmful chemicals such as antimicrobial drugs.
        c) By increasing the amount of the normal substrate, competitive inhibition can be overcome, but doing that has no effect on allosteric inhibition.

6. As a biological catalyst, enzymes have several important characteristics. Name them.

*    Like all catalysts, they speed up the rate of a chemical reaction, and they are not used up in the reaction. Also, they are specific and each one only speeds up the rate of a specific reaction. Anything that affects the structure of an enzyme such as pH, salt concentration (ionic strength), and temperature will affect the activitiy of the enzyme. Also, they are saturable.

7. What is the function of NAD, NADP, and FAD in metabolism?

*    They accept electrons (and hydrogen atoms) removed from carbon atoms during metabolism.

8. What is the difference between electrons and hydrogen ions?

*    This is important, because catabolism is all about removing electrons until the last steps where everything depends on hydrogen ions. A hydrogen atom that has an electron removed becomes a hydrogen ion or H+. Since H is just a proton and an electron, a hydrogen ion, H+, is a proton. Note that electrons and hydrogen ions are opposite things and must not be confused!

9. What are the fates of the electrons and the H+ ions during electron transport and chemiosmosis?

*    The electrons, in the form of complete H atoms, are accepted by oxygen to form water.  H+ ions accumulate outside the membrane to form a gradient and reenter the cell (down the concentration gradient) through the ATPase (which makes ATP) and meet up with OH- inside the cell to reform water.

10. A molecule(s) that an enzyme acts on is called a ____________ and the resulting molecule(s) is called a ________.

*    substrate     product