Microbiology 301

First Midterm Exam

You will be given an examination and a computer answer sheet. Make sure your name is on both the question and answer sheet. MARK ANSWER ON BOTH AND HAND BOTH IN.

The COMPUTER SHEET WILL NOT BE RETURNED and you are RESPONSIBLE for the correct transfer of your answers to the computer answer sheet.

The questions will be returned along with an individual student score report in a room in the laboratory area (number to be announced). If you wish to have your examination returned privately, give the proctor of the examination a note to that effect.

Choose the ONE best answer.

1. Which of the following statements is FALSE?

A. As a general rule, microorganisms are 1 mm or smaller in size.
B. All microorganisms have a procaryotic cell structure.
C. Anton van Leeuwenhoek is given credit for discovering the microbial world.
D. Bacteria are found residing in almost all environments examined including on the human body.
E. Robert Koch proved that certain human diseases are caused by bacteria.

2. Which of the following statements about bacteria is FALSE?

A. The binomial system of nomenclature used to name plants and animals is used to name bacteria.
B. They are the smallest of the microorganisms.
C. They all have a procaryotic structure.
D. The archaebacteria differ from the eubacteria in having a eucaryotic cell structure and their cell wall lacking peptidoglycan.
E. The electron microscope has better resolving power and magnification than a light microscope.

3. Which of the following statements about the Gram Stain/reaction are TRUE?

1. The Gram stain is an important first step in the identification of eubacteria.
2. The Gram Stain is used to determine if a bacterium is motile or not.
3. Two bacteria having the same Gram reaction and shape are identical (same genus and species).
4. The presence of purple and red bacteria following Gram staining of a culture means you may be working with a mixed culture.
5. Gram-positive bacteria appear red following staining.

A. 1, 3 B. 2, 3, 4 C. 1, 5 D. 1, 4 E. All of the above

4. A term describing spherical bacteria that remain in chains following cell division is streptococci.

A. True
B. False

5. Which of the following statements about the glycocalyx layer of bacteria is FALSE?

A. The removal/loss of this layer will result in cell lysis.
B. The chemical composition of glycocalyx can vary from genus to genus and even within a species.
C. It may contribute to the pathogenicity of a species by preventing phagocytosis by macrophages.
D. Synthesis of this layer may be nutritionally controlled.
E. In some bacteria this layer is used for cell attachment.

6. Which of the following statements is FALSE?

A. In certain bacteria, motility occurs in the absence of flagellum(a).
B. A bacterium with flagella over its entire surface is referred to as a peritrichously flagellated bacterium.
C. The part of the flagellum that anchors the structure to the cell is the basal body structure.
D. The flagellar filament is composed of identical protein subunits called flagellin. The order of amino acids in this protein is identical in all bacteria.
E. The eucaryotic flagellum generates motion by moving up and down, the bacterial flagellum(a) by rotating in a clockwise or counter clockwise direction. If more than one bacterial flagellum is present they all rotate in the same direction.

7. For the eucaryotic and procaryotic flagellum to generate motion energy must be provided in the form of ATP.

A. True
B. False

8. Which of the following statements about pili and/or fimbriae is FALSE?

A. They are surface appendages found on some bacteria.
B. A cell may have more than one type of pili/fimbriae on its surface.
C. In some cases they may be used for cell attachment.
D. May contribute to the pathogenesis of a bacterial species.
E. In the absence of a flagellum(a), these structures are used to move to a desired location.

Use the following Key to answer questions 9 through 12. An answer may be used more than once.

A. Gram-negative bacteria
B. Gram-positive bacteria
C. Mycoplasma pneumoniae
D. Archaebacteria
E. More than one of the above

9. The cell wall appears as two distinct layers when viewed through an electron microscope.

10. Sterols are present in the cytoplasmic membrane.

11. Peptidoglycan is the major chemical component of the cell wall.

12. The cell wall has endotoxic activity.

13. For penicillin to be effective, bacterial cells must be actively synthesizing peptidoglycan.

A. True
B. False

14. Lysozyme causes bacterial lysis by breaking the covalent bond between NAG and NAM, the two repeating subunits of peptidoglycan.

A. True
B. False

15. Which of the following statements is FALSE?

A. The cytoplasmic membrane of bacteria consists of a phospholipid bilayer, with many different proteins inserted into this structure.
B. The bacterial cell membrane is involved in the generation of metabolic energy, a function absent in the eucaryotic cytoplasmic membrane.
C. Transport by facilitated diffusion allows concentration of molecules inside a cell.
D. Transport by active transport requires the participation of membrane proteins known as permeases, and an expenditure of metabolic energy.

16. Which of the following statements is FALSE?

A. Bacteria have a single chromosome.
B. Plasmids are RNA molecules that contain genetic information not present on the bacterial chromosome.
C. As a group, bacteria can accumulate several types of reserve material, but generally only one type of reserve is made by any one species.
D. Phosphate is stored within a bacterium as polyphosphate, long chains of phosphate, also known as metachromatic granules or volutin granules.
E. The 70S bacterial ribosome is composed of a 50S and 30S subunit.

17. Which of the following statements about endospores/sporulation are TRUE?

1. Sporulation is a characteristic of bacteria of the genus Bacillus and Clostridium.
2. Endospores would be present during the early exponential phase of growth of bacteria capable of sporulating.
3. Endospores are resistant to boiling, but not autoclaving.
4. Endospores show little to no metabolic activity.
5. Bacteria are induced to sporulate when they sense that the environment is no longer conducive to growth or harmful.

A. 2, 3 B. 4, 5 C. 1, 3, 4, 5 D. 1, 2, 4 E. All of the above

18. Which of the following statements is FALSE?

A. A pure culture is defined as a population of cells derived from a single cell.
B. The basic principle of the streak plate technique is to take a finite number of bacteria and dilute them over a large surface in order to isolate individual cells.
C. All chemoheterotrophs have the same growth requirements.
D. A minimal medium for one species may not satisfy the growth requirements for another species.
E. The composition of a medium may alter the generation time of a species.

19. Chemolithotrophic bacteria obtain their.

A. carbon and energy from organic molecules.
B. energy from inorganic molecules and their carbon from CO2.
C. energy from light and their carbon from organic molecules.
D. energy from organic molecules and their carbon from CO2.

20. A medium that contains something in it to inhibit the growth of unwanted bacteria, but not the bacterium you are trying to isolate, is referred to as an enriched medium.

A. True
B. False

21. The advantages of the viable cell count method over the direct (total) cell count method are:

1. Cell numbers are more quickly determinable.
2. Only the number of living cells is determined.
3. Cell growth is not required.
4. Cell numbers in low density cultures (106 bacteria/ml or less) can be determined accurately.

A. 1, 2 B. 2, 3 C. 3, 4 D. 2, 4 E. All of the above

22. Which of the following statements about bacterial growth in a closed system is FALSE?

A. A finite amount of nutrients is provided in the growth medium.
B. As growth occurs, the cultural environment changes.
C. During the lag phase, bacteria show no metabolic activity.
D. The generation time of the culture is determined during the log phase of growth.
E. Cells taken from the exponential phase of growth and placed in fresh medium of the same composition would exhibit little to no lag phase.

23. The spoilage of refrigerated foods is most often due to mesophilic bacteria.

A. True
B. False

24. Facultative anaerobic bacteria grow in the presence or absence of oxygen, but grow better aerobically.

A. True
B. False

25. Aerotolerant bacteria require oxygen, but below the levels present in air.

A. True
B. False

26. A pure culture is grown at different temperatures, and the resultant growth patterns are shown below. How would you describe this bacterium with respect to it temperature requirement?

A. Psychrophile
B. Mesophile
C. Thermophile
D. Extreme thermophile
E. Need more information to make determination.

27. Which of the following statements is FALSE?

A. Obligate anaerobes are sensitive to oxygen because they lack superoxide dismutase and catalase or peroxidase.
B. Obligate aerobes can grow only if oxygen is present.
C. The sensitivity of bacteria to oxygen is due to toxic forms of oxygen produced during metabolism.
D. The optimum growth temperature for a bacterial species is closer to the temperature that will kill the bacterium than it is to the lowest temperature at which growth can occur.
E. As a general rule, the more sugar and/or salt present in the environment, the better off bacteria are in terms of growth and survival.

28. To impress your friend with your microbiology knowledge, you tell them that there are literally millions of bacteria in their mouth. To prove this you take 1 ml of their saliva and you do two consecutive 1:10 dilutions, followed by a 1:100 dilution. From the last tube you plate 0.1 ml onto an appropriate medium, and incubate overnight. The next day you count 175 colonies on the plate. How many bacteria/ml were in your friend's saliva?

A. 175 X 10^-4 bacteria/ml
B. 1.75 X 10⁷ bacteria/ml
C. 1.75 X 10⁶
D. 1.75 X 10⁵
E. Your friend says "who cares get me to a doctor!"

29. Which of the following statements about metabolism is FALSE?

A. Metabolism is the sum total of all of the chemical reactions occurring within a cell.
B. Anabolic or biosynthetic reactions are regarded as energy consuming and carbon generating.
C. When a chemical accepts electrons and protons, it becomes oxidized.
D. Irrespective of the growth requirements of bacteria, they must all produce the same 12 essential precursor molecules.
E. The type of metabolism carried out by a bacteria may be influenced by nutritional and/or physical factors.

Use the following answers for questions 30 through 32. An answer may be used more than once.

A. Fermentation
B. Anaerobic respiration
C. Aerobic respiration
D. None of the above
E. More than one of the above

30. The type of metabolism carried out by obligate aerobes.

31. Metabolism requires the participation of an electron transport chain.

32. The type of metabolism in which the primary electron donor is an organic molecule, and an inorganic molecule, other than oxygen, serves as the terminal electron acceptor.

33. Which of the following statements about fermentation is FALSE?

A. The terminal electron acceptor is always an organic molecule.
B. Fermentation is a metabolic process unique to bacteria.
C. The products of fermentation can be used to identify microorganisms.
D. Fermentation is not a very efficient way of extracting energy from an organic substrate.
E. Fermentation is an important process in both the preparation and spoilage of certain food products.

34. Which of the following statements is FALSE?

A. In glycolysis, the net yield of ATPs made is 2.
B. The final product of glycolysis is always pyruvic acid.
C. Reducing power in the form of NADH and FADH are made by both the glycolytic pathway and the TCA cycle.
D. Assimilating inorganic nitrogen, NH3 (NH4+), into organic carbon requires an intermediate of the TCA cycle.
E. The ATP made in glycolysis and the TCA cycle is by substrate level phosphorylation.

35. E. coli is able to carry out 3 types of metabolism (fermentation, aerobic respiration or anaerobic respiration), and which form of metabolism it uses depends on the carbon source present in the growth medium.

A. True
B. False

36. Electrochemical energy or proton motive force established by the electron transport chain can be used to produce ATP.

A. True
B. False

37. More ATP is made from the re-oxidation of one NADH by the electron transport chain than by the metabolism of one glucose molecule by lactic acid fermentors.

A. True
B. False

38. Which of the following statements is FALSE?

A. Enzymes are neither consumed or modified when they catalyze a chemical reaction.
B. The product of one enzyme may be the substrate for another enzyme.
C. The metabolism of glucose requires an initial expenditure of chemical energy.
D. In the hydrogen bacteria, H2 gas serves as the terminal electron acceptor.

39. Which of the following statements is FALSE?

A. The central dogma of molecular biology states that genetic information flows from DNA to RNA to proteins.
B. A nucleotide is composed of a 5-carbon sugar, a nitrogen-containing base, and a phosphate, all held together by covalent bonds.
C. The presence of uracil indicates that you have an RNA and not a DNA molecule.
D. Cellular RNA may be single- or double-stranded depending on the gene from which the RNA was made.

40. Which of the following statements about cellular DNA is FALSE?

A. It is composed of two strands held together by hydrogen bonding.
B. It contains the sugar deoxyribose.
C. You will always find an equal number of adenines to thymines, and guanines to cytosines.
D. To have proper base-pairing, the two strands of DNA must be twisted around each other in a alpha-helical structure, and be of opposite polarity.
E. The backbone structure consists of alternating molecules of nitrogen-containing base, sugar, nitrogen-containing base, sugar, etc.

41. Which of the following statements about DNA replication in bacteria are TRUE?

1. Each strand serves as a template for the synthesis of a complementary strand.
2. The order of bases on the newly synthesized strand is identical to the template stand.
3. Replication is initiated (started) at several sites on the DNA molecule called promoter regions.
4. Synthesis of the new strand always proceeds in the 5' to 3' direction.
5. It requires the enzymes DNA polymerase and DNA ligase.

A. 1, 2, 4 B. 3, 4 C. 1, 4, 5 D. 1, 5 E. All of the above

42. Segregation of the newly replicated bacterial genomes into the two daughter cells following binary fission occurs by mitosis.

A. True
B. False

43. Which of the following statements about transcription is FALSE?

A. Transcription allows cells to express part of their genetic potential.
B. Transcription is initiated at multiple, but distinct, sites on the DNA molecule.
C. Synthesis of RNA proceeds in the 3' to 5' direction.
D. The products of transcription are mRNA, tRNA, and rRNA.
E. Transcription is an enzyme-mediated process requiring RNA polymerase.

44. A single bacterial mRNA may encode for the synthesis of two or more distinct proteins.

A. True
B. False

45. Which of the following statements is FALSE?

A. Several ribosomes may be associated with a single mRNA.
B. The genetic code is the "dictionary" that allows cells to go from the four letter language of nucleic acids to the 20 letter language of amino acids.
C. The nucleotide sequence of an mRNA is read in groups of 3 bases, each called a codon.
D. The genetic code is said to be degenerate because some codons do not have complementary tRNA.
E. Two different codons may specify the same amino acid.

46. Which of the following statements about translation in procaryotes is FALSE?

A. Base-pairing rules are important.
B. Transcription of a message must be completed before translation of that message can begin.C. m-RNA is always read in the 5' to 3' direction.
D. The translating portion of an mRNA molecule that contains 633 bases would synthesize a protein containing 211 amino acids.

47. Using the following DNA sequence, what would be the predicted RNA sequence made from this DNA?

3'-ATGCTAAGC-5'

A. TACGATTCG
B. AUGCUAAGC
C. UACGAUUCG
D. AUGGAAAGC
E. A genetic code table is needed to determine the order of nucleotides.

48. Which of the following statements is FALSE?

A. In the "charging" of a tRNA molecule, an amino acid is covalently linked to a specific tRNA.
B. Termination of translation occurs at nonsense codons.
C. The order of amino acids in a protein is dictated by the order of nucleotides on an mRNA.
D. The eucaryotic chromosome consists of two or more double-stranded linear DNA molecules.
E. The eucaryotic mRNA can be translated immediately following its synthesis.