Download Chapter 14 Answers to Even Numbered Study Questions

PRINCIPLES OF MODERN MICROBIOLOGY
Mark Wheelis
ANSWERS TO STUDYQUESTIONS
Chapter 14
Procaryotic Microbes
2.
If we want to try to infer something about the common ancestor of all life, there are two approaches
that can give us hints. One is the presumption that characteristics shared by all or most descendents
are most likely the result of common descent, rather than convergence. Thus we can infer that most
of the basic protein synthesizing machinery, the use of DNA for information storage and RNA for
gene expression, the specifics of the genetic code, the use of ATP, NADH, and other cofactors in
their modern roles, the enzymes of central metabolism and of biosynthesis, and many other
common traits were already present in the most recent common ancestor.
We can also, with much less certainty, reason that features of early branching lineages, and of
lineages that appear to have undergone much less evolutionary change than others, are likely to be
more similar to the common ancestor than more recently diverging and more rapidly changing
lineages. This reasoning suggests that the common ancestor was likely a thermophile or extreme
thermophile (reasonable on environmental grounds also, as the early earth was much hotter than
now). It was probably an anaerobe (also consistent with what we know of the early atmosphere),
and it probably used sulfur compounds as electron donor or acceptor. Of course, these conclusions
must be very tentative.
4.
Many proteobacteria cause human disease: the enteric bacteria, the vibrio group, the
pseudomonads, and the rickettsias. So do a number of gram positive bacteria, spirochetes, and
chlamydia. No archaea are known to cause human disease. (Note: a number of other groups contain
human pathogens; only those that are mentioned in this chapter are included here.)
6.
All bacteria contain murein in their cell envelope, with the following exceptions: the
planctomycetes (which have a protein envelope), the chlamydia (which have a peptidoglycan that
lacks muramic acid), and the mycoplasmas within the gram positive bacteria (which have no
envelope, but which have abundant glycolipids).