Download Prescott`s Microbiology, 9th Edition Chapter 18 – Microbial

Prescott’s Microbiology, 9th Edition
Chapter 18 – Microbial Genomics
GUIDELINES FOR ANSWERING THE MICRO INQUIRY QUESTIONS
Figure 18.1 What is the function of the 3’-OH during DNA synthesis?
This is where the 5’ phosphate of the next nucleotide is covalently attached during elongation.
Figure 18.4 Why is it important that the DNA to be sequenced is immobilized in all three of these
techniques?
With a flow cell, unless the DNA was attached to the substrate, it would flow away.
Figure 18.6 Which step (or steps) in this process is (are) replaced by PCR amplification and
immobilization of fragments to a solid support in the post-Sanger sequencing techniques?
Comparing this figure to 18.4, the major difference is that the Sanger steps of gel electrophoresis
and cloning are replaced by PCR and immobilization, which results in a process that is much
faster and less expensive.
Figure 18.9 Which amino acids are most highly conserved?
The ones in the putative membrane targeting sequence.
Figure 18.11 Based on this genomic reconstruction, can you determine if T. palidum has a
respiratory or fermentative metabolism?
Since electron transport chain pathways are not present, respiration is not possible. Thus
fermentation is the mode of catabolism.
Figure 18.13 Based on your interpretation of the data, identify two genes that are strongly induced and
two genes that are strongly repressed.
A ratio number of one means the expression is unchanged in the two conditions. Strongly induced genes
have light red colors, and a high fold ratio number. Examples would be DR0422, DR1359, and DR0207.
Strongly repressed genes have light green colors and a low ratio number. Examples would be DR1337,
DR1998, and DR1146.
Figure 18.15 How would determining the amino acid sequence of a 30 amino acid residue
peptide differ from determining the amino acid sequence of a 200,000 dalton protein?
The peptide would generate a few fragments, while the protein would generate dozens.
Figure 18.18 Two strains of E. coli are shown in this figure. One is a human pathogen and one
is not. Explain why genome size cannot be used to determine which is pathogenic.
The nonpathogenic strain is K-12, with 4.64 million bp, and the pathogenic strain is O157:H7,
with a 5.53 million bp genome. K-12 is a lab strain, while O157:H7 is a virulent foodborne
strain which causes bloody diarrhea. It contains a number of protein toxin genes. Sometimes the
evolution of pathogenesis involves acquisition of additional genes, sometimes it involves the
loos of genetic material. Mycoplasma genitalium and Chlamydia trachomatis are pathogens as
well.
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