Microbiology Answers

You can smell sulfur when boiling eggs. What amino acids do you expect in the egg?

DNA polymerase I (Pol I) of E. coli consists of three functional parts (domains): an N-terminal domain with 5´ to 3´ exonuclease activities required for removal of the RNA primer, a central domain responsible for 3´ to 5´ exonuclease proofreading, and a C-terminal domain with polymerase activity. Pol I is thought to simultaneously remove RNA primers and fill in the gaps that result. A group of proteins known as RNaseH also have 5´ to 3´ exonuclease activity and can thus remove RNA primers. However, they lack the other two functions observed for Pol I. Predict the ability of the following mutants to replicate DNA:

(1) a strain with a mutant gene encoding Pol I such that it no longer has polymerase activity (but retains both types of nuclease activities)

DNA polymerase I (Pol I) of E. coli consists of three functional parts (domains): an N-terminal domain with 5´ to 3´ exonuclease activities required for removal of the RNA primer, a central domain responsible for 3´ to 5´ exonuclease proofreading, and a C-terminal domain with polymerase activity. Pol I is thought to simultaneously remove RNA primers and fill in the gaps that result. A group of proteins known as RNaseH also have 5´ to 3´ exonuclease activity and can thus remove RNA primers. However, they lack the other two functions observed for Pol I. Predict the ability of the following mutants to replicate DNA:

(1) a strain with a mutant gene encoding Pol I such that it no longer has polymerase activity (but retains both types of nuclease activities);   

(2) a strain without RNaseH proteins;

You have isolated several E. coli mutants: Mutant #1 has a point mutation in the -10 region of the promoter of a structural gene encoding an enzyme needed for synthesis of the amino acid serine. Mutant #2 has a mutation in the -35 region in the promoter of the same gene. Mutant #3 is a double mutant with mutations in both the -10 and -35 region of the promoter of the same gene. Only Mutant #3 is unable to make serine. Why do you think this is so?

1. Why is fungal growth rate slower than bacterial growth rate? (5 marks)

2. List 4 ways in which fungi are useful to humans. (4 marks)

3. List 4 ways in which fungi are harmful to humans. (4 marks)

4. Why is it difficult/takes a long time to treat fungal infections in humans? (3 marks)

5. What are some distinctive features of fungi that can be used for its morphological characterization and identification? (4 marks)

Consider the growth of microorganism in batch culture, inoculated at a biomass concentration of 0.1g/L growing as the limiting substrate with the initial concentration S_° =10 g/L. After a lag time of 3 h, the culture grows exponentially with a minimum doubling time of 2h. Stationary phase is reached after a total time of 14 h. Assume that there was no death phase. Calculate the total time in culture to reach stationary phase if S_° were 2g/L, assuming that this concentration is also sufficient to support maximal growth (i.e., S>>Ks over the entire fermentation). 

Which of the following organisms is larger in size, a bacterium with 2 micrometer or a chloroplast with 0.003 millimeter? State your reasons and show your computation.