Question

Figure 8.1 The following results were obtained from a replica-plating experiment: 1 2 3 4 5 5 Complete Glucose minimal salts (OMSA) GMSA + streptomycin GMSA + leucine GMSA +valine + streptomycin GMSA + leucine + streptomycin 20) Please consider Figure 8.1 carefully Which colonies are leucine auxotrophs? A) 1, 2, 3, and 9 B) 1, 2, 3, 4, 6, 8, and 9 C) 4,6, and 8 D) 3, 4, 8, and 9 21) Please consider Figure 8.1 carefully. Which colonies are streptomycin resistant? A) 3 and 9 B) 3,4,5,8, and 9 C) 3, 4, 8, and 9 D) 3,5, and 9 22) DNA probes I. are essentially short pieces of DNA of a particular chosen sequence. II. are labelled so that we can observe them via fluorescence or radioactivity, III. rely on complementary base pairing in order to bind to their target DNA. TV. allow us to look for the presence of specific known sequences of DNA V. let us identify specific proteins. VI. are never labelled with a fluorescent or radioactive marker. A) IV, V, and VI only. B) I only. C) I, II, III, and IV only. D) III, IV, and VI only. 23) Which of the following is NOT used as a criterion to classify viruses? A) Morphology B) Size C) Biochemical tests to measure metabolic activity. D) Nucleic acid SHORT ANSWER. Please answer the question(s) in the space provided. 36) You are studying the metabolic capabilities of a species of bacteria by growing cultures on different carbon sources and comparing their mRNA expression profiles using microarray analysis. You grow one culture on the single carbon compound methanol, and another culture (same species) on the four carbon compound succinate. You extract the mRNA from each culture and use microarray analysis to obtain the following expression ratios for three sample genes comparing growth on methanol to growth on succinate (ie, ratio is methanol succinate). Gene A: 0.03; Gene B: 27.8; Gene C: 1.001 For each gene, propose a general role based on this expression data that demonstrates your understanding of gene expression and microarrays. Gene A: Gene B: Gene C

Answer 1

• Minimal media contains nutrients in the minimal amount for survival of bacteria.
• Prototroph and auxotroph are terms referred to strains of bacteria on their ability synthesize nutrients like amino acids, nucleic acids, minerals, vitamins etc.
• Prototrophs are wildtype strains, which can synthesize nutrients required for their cellular functions.
• These bacteria can grow on minimal or basal media without supplementary nutrients.
• Auxotrophs are mutant strains, which have lost the capabilities of synthesizing specific nutrients.
• Auxotroph can grow on minimal media, only when the specific nutrient (as per the auxotroph mutant) is supplemented to the media.

20. Answer: C

In the given case:

• Minimal media has colonies 1,2,3,9.
• Thus, these are prototrophs.
• On supplementing leucine, colonies 4,6 and 8 also appear.
• Thus, leucine auxotrophs are 4,6 and 8.

21. Answer: B

• Three plates are used with antibiotic Streptomycin.
• Thu, colonies in all the plates together comprises of Streptomycin resistant colonies, which are  3,4, 5, 8 and 9.