Chapter 5

Arsenic is a poison that exists in two states in the environmentarsenite $\left({\mathrm{H}}_2{\mathrm{AsO}}_3^{-}\right)$and arsenate $\left({\mathrm{H}}_2{\mathrm{AsO}}_4^{-}\right)$. Arsenite dissolves in water, making the water dangerous to drink. Arsenate is less soluble and binds to minerals, making this form of arsenic less toxic in the environment. Some strains of the bacterium Thermus oxidize arsenic in an aerobic environment but reduce arsenic under anaerobic conditions. In case of arsenic contamination of water, how could scientists use Thermus to remediate the problem?

Why is the pentose phosphate pathway half as energy efficient as glycolysis?

Describe how bacterial fermentation causes milk to sour.

Giardia intestinalis and Entamoeba histolytica are protozoa that live in the colons of mammals and can cause life-threatening diarrhea. Interestingly, these microbes lack mitochondria. What kind of pathway must they have for carbohydrate catabolism?

Two cultures of a facultative anaerobe are grown in the same type of medium, but one is exposed to air and the other is maintained under anaerobic conditions. Which of the two cultures will contain more cells at the end of a week? Why?

What is the maximum number of molecules of ATP that can be generated by a bacterium after the complete aerobic oxidation of a fat molecule containing three 12-carbon chains? (Assume that all the available energy released during catabolism goes to ATP production.)

Sulfanilamide, which inhibits folic acid producing microbes to synthesize nucleic acids, has no effect on humans. Explain.

Cyanide is a potent poison because it irreversibly blocks cytochrome $a_3$. What effect would its action have on the rest of the electron transport chain? What would be the redox state (reduced or oxidized) of ubiquinone in the presence of cyanide?

How do the processes of oxygenic photosynthesis and aerobic respiration complement one another?

Members of the pathogenic bacterial genus Haemophilus require ${\mathrm{NAD}}^{+}$and heme from their environment. For what purpose does Haemophilus use these growth factors?