Saturday, December 1, 2007

Concept 27.3

Question:
I. Explain how molecular systematics has greatly increased our understanding of prokaryotic phylogeny.

Answers:
a) Before molecular systematics, taxonomists classified prokaryotes according to phenotypic characters that did not clarigy evolutionary relationships. Molecular comparisons indicated key divergences in prokaryotic lineages.


Question:
II. What do syphilis and Lyme disease have in common?

Answer:
a) The two pathogenic spirochetes unexpectedly share an ATP synthase. The organism that causes Lyme disease is a bacterium, Borrelia burgdorferi, which was cultured from the midgut of Ixodes ticks in the mid-1980s. One of the most infamous relatives of this bacterium, Borrelia burgdorferi, is Treponema pallidum, the bacterium that causes syphilis. In contrast to Lyme disease, syphilis is not a modern affliction; it was first recognized in the 15th century in Europe. It is similar to B. burgdorferi in that it is a spirochete with a relatively small genome and requires a host to survive; however, at the genomic level, the two organisms are not very closely related to each other at all.
b) both diseases are caused by spirochetes.

Question:
I. What characteristics enable some species of Archaea to live in extreme environments?

Answers:
a) The ability of various archaea to use hydrogen, sulfur, and other chemicals as energy sources and to survive or even thrive without oxygen enables them to live in environments where more commonly needed resources are not present.

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