Microbiology 2124
Exam 2
Oct. 21, 1998
David Demezas
General Instructions: Answer multiple choice questions on the test sheet. Answer other questions in the space provided on the test sheet. Be sure that you answer the question in complete sentences. Write your name on all pages of the test.
Multiple Choice (2.5 pts each). Choose the most correct answer and mark the corresponding letter on the blank provided to the left of the question.
1. Bacteria multiply by a process called _________.
A. meiosis
B. binary fission
C. replication
D. mitosis
E. fusion
2. The growth of a bacterial population is plotted on semilogarithmic paper. The growth curve will be _______.
A. linear
B. curvilinear
C. sigmoid
D. exponential
E. hyperbolic
3. Which of the following will NOT result in a lag phase?
A. Stationary phase cells inoculated into the same medium.
B. Damaged cells inoculated into the same medium.
C. Cell grown in rich medium inoculated into poor medium.
D. Exponentially growing cells inoculated into the same medium.
E. All of the above will result in a lag phase.
4. Which of the following is NOT characteristic of stationary phase?
A. Growth rate equals zero.
B. Nutrients are depleted.
C. Waste products are accumlating.
D. Growth rate is maximal for the species of bacteria.
E. All of the above.
5. A viable cell count is obtained by _________.
A. the spread plate method
B. the pour plate method
C. direct microscopic counts
D. optical density (i.e. turbidity)
E. A and B
6. The usual type of bacteria used in our teaching laboratory (e.g., Escherichia coli) would be classified as a ______ based on its growth temperature requirements.
A. psychrophile
B. thermophile
C. mesophile
D. extreme thermophile
E. psychrotroph
7. A species of fresh water bacteria makes _________ to counter the loss of water from their cytoplasm to the environment when they are placed in salt water.
A. reduced solutes
B. compatible solutes
C. noncompatible solutes
D. oxidized solutes
E. None of the above.
8. Which of the following enzymes degrades hydrogen peroxide to oxygen and water?
A. catalase
B. super oxide dismutase
C. peroxidase
D. reductase
E. resazurin
9. T or F - The fatty acids of the plasma membrane of a thermophilic bacteria are mainly unsaturated fatty acids
10. Microorganisms that can only grow in environments where the oxygen level is reduced from that in air are ________.
A. facultative aerobes
B. strict anaerobes
C. microaerophiles
D. aerobes
E. none of the above
11. "Central dogma of molecular biology" states that genetic information flows from _____
A. RNA through DNA to protein.
B. protein through RNA to DNA
C. DNA through protein to RNA
D. DNA through RNA to protein
E. RNA through protein to DNA
12. Nucleotides are composed of ___________.
A. a sugar, a nitrogenous base, and phosphate groups
B. a fatty acid, nitrogenous base, and sulfate groups
C. a sugar and phosphate groups
D. a peptide, nitrogenous base, and phosphate groups
E. an amino acid and phosphate groups
13. T or F - Replication in bacteria is usually bidirectional.
14. ______ forms the phosphodiester bond between adjacent Okazaki fragments.
A. DNA polymerase I
B. DNA ligase
C. DNA polymerase III
D. primase
E. topoisomerase
15 The primer in DNA replication is _________.
A. an RNA starter sequence with a free 3´-OH group
B. an RNA starter sequence with a free 5´-OH group
C. a DNA starter sequence with a free 3´-OH group
D. a DNA starter sequence with a free 5´-OH group
E. a DNA starter sequence with a free 5´-phosphate group
16. Which of the following statements about RNA is False?
A. mRNA, tRNA and rRNA are the products of transcription.
B. rRNA is incorporated into ribosomes.
C. All RNAs are translated into polypeptides.
D. tRNAs carry amino acids to the growing polypeptide.
E. Only mRNA is translated into polypeptides.
17. T or F - A tRNA may carry several different amino acids to the growing polypeptide.
18. Which of the following statements about promoters is incorrect?
A. - 10 region or the Pribnow box sequence is semiconserved among promoters
B. - 35 region is identical among all promoters.
C. -10 region is identical among all promoters.
D. - 35 region is semiconserved among all promoters.
E. B and C
For questions 19 and 20
DNA sequence: 3´ - ATG ATA CGT ACC AGT TGA CTA GTA - 5´
19. The mRNA transcript from the above DNA seqeunce is ________.
A. 3´ - ATG ATA CGT ACC AGT TGA CTA GTA - 5´
B. 5´ - TAC TAT GCA TGA TCA ACT GAT CAT - 3´
C. 5´ - UAC UAU GCA UGG UCA ACU GAU CAU - 3´
D. 5´ - ATG ATA CGT ACC AGT TGA CTA GTA - 3´
E. 3´ - UAC UAU GCA UGG UCA ACU GAU CAU - 5´
20. The translation product is _______.
A. tyr - tyr - ala - trp - ser - thr - asp - his
B. tyr - tyr - ala- stop
C. his - asp - thr - ser - trp - ala - tyr - try
D. his - asp - thr - stop
E. None of the above is correct.
21. Enzymatic activity of a pathway (e.g., biosynthesis of an amino acid) can be controlled by the endproduct inhibiting the first enzyme of the pathway. This is referred to as _________.
A. saturation
B. negative control
C. positive control
D. substrate inhibition
E. feedback inhibition
22. T or F - Regulation of a gene by a repressor is often referred to as negative control.
23. A constituitive enzyme is an enzyme in which _______.
A. synthesis is constant
B. control is negative
C. control is positive
D. there is allosteric regulation
E. there is catabolite repression
24. Repressors and the catabolite activator protein are examples of ____________.
A. catalytic enzymes
B. allosteric proteins
C. structural proteins
D. terminators
E. coinducers
25. T or F - The regulation of the maltose operon and catabolite repression of the lactose operon are examples of positive control.
26. The repression of the lactose operon by the presence of glucose is mediated through ________.
A. elevated level of cyclic AMP in the cell
B. low levels of cyclic AMP (cAMP) in the cell
C. a lac repressor /glucose complex binding to the lac operator
D. glucose binding to the lac operator
E. None of the above.
27. Genes for utilizing maltose are scattered throughout the chromosome of Escherichia coli and are under control of the same regulatory protein. The maltose-utilizing genes are an example of a _____.
A. an operon
B. regulon
C. stimulon
D. modulon
E. none of the above
28. Which of the following statements is False about cells in the early part of the second phase of diauxic growth in a glucose/lactose based medium?
A. The lac repressor is bound to the inducer and cannot bind to the operator region.
B. The levels of cyclic AMP are elevated relative to the first phase of growth.
C. The lac operon is induced.
D. cAMP/CAP is bound to the CAP binding site.
E. All of the above statements are true.
29. The two component regulatory system involved in signal transduction are composed of ______________.
A. repressors and corepressors
B. activators and inactivators
C. sensors and response regulators
D. transducers and corepressors
E. None of the above.
30. Attenuation, an effective means of regulating amino acid biosynthetic genes in bacteria, requires _________.
A. a repressor
B. a activator protein
C. coupling of transcription and translation
D. an inducer
E. feedback inhibition
31. A strain of Escherichia coli that requires an amino acid for growth is called a ___.
A. autotroph
B. lysogen
C. prototype
D. prototroph
E. auxotroph
32. T or F - A point mutation (i.e., a base pair substitution) in the third position of a codon always lead to missense mutations.
33. You obtained a mutant strain of E.coli through chemical mutagenesis using 5- bromouracil. Subsequently you found that the strain had reverted back to the wildtype phenotype in high frequency. What type of mutant did you obtain from chemical mutagenesis?
A. base-pair substitution
B. microdeletion
C. microinsertion
D. pyrimidine dimer
E. suppressor mutant
34. Ultraviolet light is used in germicidal lamps to kill bacteria. Ultraviolet light in the 260 nm region causes __________, which may be lethal, to form in DNA.
A. microdeletions
B. point mutations
C. pyrimidine dimers (e.g., thymine dimers)
D. microinsertions
E. None of the above.
35. The ______ is used to determine if a chemical is mutagenic and potentially carcinogenic.
A. complementation test
B. Ames test
C. transposon test
D. penicillin-test
E. fixation test
36 - 40. Match each term with the appropriate statement (A-E) about it.
36. Transformation A. F-factor is integrated in chromosome
B. Recipient cell
37. Transduction C. Absorbtion of DNA from the environment
D. Bacteriophage-mediated DNA transfer cell
38. Hfr E. F-factor separate from chromosome
39. F+
40. F-
Each of the following is worth 10 pts. Write your answers on the sheet of paper provided.
41. A culture of bacteria with a generation time (g) of 0.2 will grow from 3 x 103 to 1011 cells in how many hours?
42. Draw a replication fork and place and/or label the following clearly:
* 5´ and 3´ end of both parent strands of DNA
* leading strand with 5´ and 3´ end labelled
* DNA polymerase III
* helicase
* single-stranded binding proteins
* primase
* lagging strand
* using arrows, indicate the direction of DNA synthesis of both strands.
43. Copy the below diagram to your paper twice for question 43a and 43ba) Draw the interaction of repressor and the lac operon in the absence of lactose. Be sure to include the repressor, promoter, structural genes, operator, RNA polymerase and inducer. Also indicate whether the operon is expressed or not.
b) Draw the interaction of the repressor and the lac operon in the presence of lactose. Be sure to include the repressor, promoter, structural genes, operator, RNA polymerase and inducer. Also indicate wherther the operon is expressed or not.
44. a) Draw a mating between an F+ and an F- Escherichia coli cell. Indicate the outcome of this mating.
b) Draw a mating between an Hfr and an F- E. coli cell. Indicate the outcome of this mating.
