Microbiology 2124
Exam 2
Oct. 22, 1999
David Demezas

General Instructions: Answer multiple choice questions on your scantron 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 your scantron sheet.

1. The population size of bacteria increase by _________.
A. cloning
B. binary fission
C. replication
D. mitosis
E. meiosis

2. Given a population of bacteria with an initial population of 1 x 10⁶ cfu/ml and a population of 1 x 10⁹ cfu/ml after 1 hour. What is the most likely doubling time (generation time; g) of this culture?
A. 0.1 hours
B. 1 hour
C. 2 hours
D. 0.25 hours
E. 4 hours

3. Organisms that have adapted to live in the bodies of animals (e.g., you) are classified as ______.
A. psychrophile
B. thermophile
C. mesophile
D. extreme thermophile
E. psychrotroph

4. Which type of bacterium grows with or without oxygen in the presence of a suitable electron acceptor?
A. obligate anaerobe
B. obligate aerobe
C. facultative anaerobe
D. microaerophile
E. aerotolerant aerobe

5. As nutrients are depleted and waste products accumulate in a culture of bacteria, the growth of the population begins to slow and the culture enters the __________.
A. lag phase
B. log phase (syn. exponential phase)
C. stationary phase
D. Death phase
E. None of the above.

6. True (A) or False (B). A mid-log phase culture of bacteria growing in nutrient broth is inoculated into fresh, sterile nutrient broth. The new culture will not go through a lag phase as it grows.

7. Which of the following is used to determine the total number of cells (i.e., living and dead) in a culture?
A. spread plate counts
B. turbidity
C. microscopic counts
D. dry weight
E. pour plate counts

8. Which of the following enzymes converts hydrogen peroxide to oxygen and water?
A. oxidase
B. carboxylase
C. catalase
D. polymerase
E. ligase

9. Which of the following elements makes up the greatest percentage of bacteria by weight?
A. oxygen
B. phosphorous
C. nitrogen
D. iron
E. carbon

10. Mannitol salts agar with 7.5% salt and a pH indicator is an example of __________.
A. a selective medium only
B. a differential medium only
C. a selective and differential medium
D. none of the above.

11. True (A) or False (B). The chemical composition of complex media is well defined.

12. The time required to kill a suspension of bacteria held at a given temperature is referred to as _____.
A. decimal reduction time
B. thermal death time
C. thermal death point
D. none of the above.

13. True (A) or False (B). The autoclave operates at 15 lbs/ square inch pressure and 121 ^oC for 10 -15 minutes to sterilize moderately sized loads.

14. Ultra-violet lights are germicidal because ultra violet wavelengths of light cause ________, that are harmful to a bacterium, to form.
A. adenine dimers
B. guanine dimers
C. cytosine dimers
D. thymine dimers
E. all of the above

15. Food spoilage in the refrigerator is caused by _________.
A. mesophiles
B. psychrophiles
C. barophiles
D. thermophiles
E. psychrotrophs

16. True (A) or False (B). The volume of the medium bears no relationship to the time required for sterilization in the autoclave.

17. _______ are sufficiently non-toxic to be used on living tissue (e.g., your face).
A. Disinfectants
B. Antiseptics

18. Which of the following macromolecules is not a frequent target of chemical disinfectants?
A. plasma membrane
B. proteins
C. chromosome
D. All of the above are targets.
E. None of the above are targets.

19. The most widely accepted method for the disinfection of milk that allows it to retain its palatability is _______.
A. autoclaving
B. pasteurization
C. ultra violet light
D. none of the above
E. all of the above

20. True (A) or False (B). Non-ionizing radiation sterilizes materials by producing highly reactive hydroxyl radicals that react with and damage DNA and other macromolecules.

21. "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

22. DNA serves as a template for the synthesis of _______ by complementary base-pairing.
A. RNA and protein
B. DNA and RNA
C. RNA only
D. DNA and protein
E. DNA only

23. If you determined that the DNA of a species of bacteria was 27% cytosine, you would correctly predict that there is ______ thymine in the DNA.
A. 27%
B 23%
C. 73%
D. 0%

24. You have discovered a new drug that inhibits DNA ligase. This drug will prevent ________.
A. the formation of peptide bonds between adjacent nucleotides in a polynucleotide strand
B. the formation of phosphodiester bonds between adjacent amino acids in a polynucleotide strand
C. the formation of peptide bonds between adjacent amino acids in a polypeptide
D. the formation of phosphodiester bonds between adjacent nucleotides in a polynucleotide strand
E. hydrolysis of DNA into nucleotides

25. 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.

26. Which of the following statements about replication is False?
A. DNA polymerase adds incoming nucleotides to the 3 prime end of the growing polynucleotide strand.
B. DNA helicase and single stranded binding proteins are required to unwind the double helix of the DNA and hold the two strands of polynucleotides apart during replication.
C. Okazaki fragments make up the leading strand of DNA.
D. Replication begins at OriR and proceeds in both a clock-wise and counter clock-wise direction.
E. A single RNA primer is needed to begin synthesis on the leading strand of DNA.

27. How many nucleotides constitute a codon?
A. 1
B. 2
C. 3
D. 4
E. 6

28. True (A) or False (B). In enzyme repression and induction, the repressor is usually an allosteric protein.

29. Enzymatic activity of a pathway (e.g., biosynthesis of an amino acid) can be controlled by the endproduct inhibiting the enzymatic activity of the first enzyme in the pathway of the amino acid biosynthesis. This is referred to as _________.
A. saturation
B. enzyme repression
C. positive control
D. substrate inhibition
E. feedback inhibition

30. The repression of the lactose operon by the presence of glucose is mediated through ________.
A. elevated level of cyclic AMP in the cell
B. depressed 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.

31. An operon is composed of _____________.
A. promoter, operator and structural gene(s)
B. promoter and operator only
C. operator and structural gene(s) only
D. promoter and structural gene(s)
E. none of the above

32. The function of the repressor of the lac operon is to ____________.
A. bind to the promoter in the absence of lactose
B. convert lactose to allolactose
C. bind to the promoter in the presence of lactose
D. bind to the operator in the presence of lactose
E. bind to the operator in the absence of lactose

33. A mutation of the base-pair substitution type that leads to premature termination of translation is called a(n) ____________.
A. silent mutation
B. missense mutation
C. non-sense mutation
D. deletion
E. insertion

34. Intercalating agents such as acrodine orange cause mutations by _________.
A. resembling normal nucleotides and causing basepair substitutions
B. modifying normal bases in the chromosome and causing basepair substitutions
C. inserting themselves between bases, therefore, spreading them apart and causing microdeletions
D. inhibiting DNA polymerase
E. by inhibiting RNA primase

35. True (A) or False (B). All point mutations in a structural gene lead to changes the amino acid sequence of the polypeptide.

36. Consider a mutation which occurs in which the change is from UAC to UAU, where both triplets code for the amino acid tyrosine. This is an example of a _____.
A. silent mutation
B. nonsense mutation
C. missense mutation
D. a point mutation
E. A and D

37. True (A) or False (B). Unlike mutations in eukaryotic organisms, all mutations in bacteria are inheritable.

Match the term with the correct definition from the right-hand column.

41. Given the following sequence of a gene, transcribe and translate it into a polypeptide. Be sure to show the product of transcription and translation.
5’ -GGATTCACATGTTTGTAGTCATTTAAATGGGCCGCGCAT-3’
Codon table
A) Transcription product:

B) Translation product:

42.

A) Diagram the interaction of the lac repressor and the lac operon in the absence of the inducer. This operon is or is not (circle one) expressed.

____p lacI_____p__lacZ___________lacY__________lacA________________

B) Diagram the interaction of the lac repressor and the lac operon in the presence of the inducer. This operon is or is not (circle one) expressed.

____p lacI_____p__lacZ___________lacY__________lacA________________