Prokaryotes & Viruses
Types of Prokaryotes
Classwork
1. What are the two major categories of prokaryotic organisms?
2. Why would a doctor recommend that you consume a probiotic while taking
antibiotics to fight an infection?
3. What is an extremophile?
4. Which group of prokaryotes is most likely to contain extremophiles?
5. Explain why scientists believe that archaeans are more closely related to
eukaryotes than bacteria.
Homework
6. Identify two ways in which bacteria can be helpful to the human body.
7. Provide two reasons why bacteria greatly outnumber mammals in number and
diversity on Earth.
8. What characteristics of archaea would allow them to be categorized as
extremophiles?
9. Taking into account the recent categorization of archaeans, explain why science
is often times a malleable subject.
Structure & Function
Classwork
10. Describe what the name Streptococcus would indicate to you regarding the
shape and organization of a specific bacterium.
11. Identify one external cellular feature that distinguishes bacteria from animal cells.
12. Would a bacterium with a capsule, or without a capsule, more closely resemble a
gel-coated Tylenol pill? Why?
13. Explain the behavior you would observe in a bacterium exhibiting chemotaxis.
What organelle would most likely be involved in this process?
14. Compare fimbriae in bacterium to another object seen in nature or an artificial
object used in everyday life.
15. Explain how pili allow for stimulating genetic diversity in bacteria.
16. In what area of a bacterium would you most likely find peptidoglycan?
17. Explain how the presence of an “F” factor could affect the lifestyle of a
prokaryote.
Homework
18. Describe what the name Staphylococcus would indicate to you regarding the
shape and organization of a specific bacterium.
19. Explain the similarities between cellulose and peptidoglycan.
20. Explain the behavior you would observe in a bacterium exhibiting phototaxis.
21. What is the difference between fimbriae and sex pili?
22. What impact would a lack of sex pili have on the bacteria gene pool?
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23. How would you identify bacteria that carried an R plasmid amongst a population
exposed to an antibiotic?
Reproduction & Gene Expression
Classwork
24. What information would the ‘locus’ of a gene reveal to an observer?
25. Reproduction in prokaryotic cells is called ________________________.
26. Taking into account the structure or bacterial chromosomes, explain why a
replication bubble exists during bacterial chromosome replication.
27. Is binary fission an example of sexual or asexual reproduction? Explain your
answer.
28. What is an operon?
29. Explain why the existence of operons in prokaryotic cells helps to demonstrate a
characteristic of living organisms.
30. Explain how the lac operon helps prokaryotic organisms conserve energy.
31. What molecule plays the role of inducer in the lac operon?
32. What role does tryptophan play in the activation or inactivation of the trp operon?
33. How does the presence of tryptophan impact the transcription of the gene that
allows for the production of tryptophan in an organism that utilizes the trp
operon?
34. Explain the role of each of the following in the utilization of operons: operator,
promoter, gene.
35. What type of symbiotic relationship is exhibited in the following scenario?
Explain your answer. A clownfish receives protection from an anemone via its
stinging tentacles, and the anemone receives food and is cleaned by the
clownfish.
36. What type of symbiotic relationship is exhibited in the following scenario?
Explain your answer. A specific strain of bacteria lives in your small intestine.
This bacteria absorbs nutrients from your body, and occasionally, when gathered
in abundance, may cause you to become sick.
37. Why would natural selection favor bacteria that are living in close proximity to
other bacteria, as opposed to bacteria living in relative isolation?
Homework
38. Describe prokaryotic chromosomes.
39. How many replication forks exist during prokaryotic chromosome duplication?
Explain your answer.
40. Where does transcription occur in a prokaryotic cell?
41. What role do repressors play in operon function?
42. In what way is using the lac operon similar to turning off the lights when you are
not in a room?
43. What is the difference between an inducible operon and a repressible operon?
44. Why would the body benefit from the inactivation of the tryptophan gene when
tryptophan is present in the body?
45. Define symbiosis.
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46. What type of symbiotic relationship is exhibited when one organism benefits and
another organism is negatively affected in a relationship?
47. Provide an example of how two bacteria, living in close proximity to each other,
may create a mutualistic relationship.
Genetic Variation
Classwork
48. Explain why mutation is more likely to increase genetic diversity at a rapid rate in
prokaryotes than in other organisms.
49. Briefly explain how Fredrick Griffith’s experiment demonstrated the process of
bacterial transformation.
50. What is the difference between sexual reproduction and conjugation exhibited in
bacteria?
51. What role do viruses play in the process of transduction?
52. Can a virus reproduce without the presence of another organism? Explain your
answer.
53. It is often said that viruses ‘infiltrate’ host cells. Explain why scientists use this
terminology to explain the life cycle of viruses.
54. Explain the difference between the lytic and lysogenic cycles.
55. Explain how temperate phages are different from viruses that utilize the lytic
cycle.
56. What does the term ‘host range’ mean in terms of viral reproduction?
Homework
57. Explain how the process of transformation can lead to genetic diversity in
prokaryotes.
58. How do sex pili allow for an increase in genetic diversity in prokaryotes?
59. Are viruses considered to be living organisms? Explain your answer.
60. Explain how viruses utilize host cells to reproduce.
61. Some scientists believe that viruses evolved in tandem with other cells. Use
what you know about virus life cycles to support this statement.
62. How could a virus that utilizes the lysogenic cycle spread throughout an
organism without immediately killing host cells.
63. Explain the term ‘obligate intracellular parasite.’
Biotech: Recombinant DNA
Classwork
64. List all the steps of the recombinant DNA process and their associated
technologies (if any).
65. Explain how the process of gel electrophoresis can be useful in determining the
identity of a gene of interest after restriction enzymes have been utilized.
66. Explain why the fact that DNA is a universal code allows scientists to produce
recombinant DNA.
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Homework
67. Why is polymerase chain reaction an important step in the genetic engineering
process?
68. Suppose you are examining a gel produced through the electrophoresis process.
How could you determine which segments of DNA contain more or fewer bases
than the others?
69. Suppose that instead of DNA being universal among all life, that each new
species utilized different nucleotides in their DNA. How could this affect the
process of genetic engineering?
Free Response
1. Compare and contrast the lac and trp operons by responding to the following
prompts:
a. Identify the lac operon and the trp operon as either an inducible operon or
a repressible operon.
b. Identify which type of operon is typically on (inducible or repressible).
c. Identify which type of operon is usually off (inducible or repressible).
d. Explain the steps that occur with a repressible operon (identify the factors
or molecules that alter the typical state of a repressible operon as well as
the following terminology: co-repressor and operator)
2. The illustration below represents how antibiotic resistant can develop within a
bacterial population. All of the circles represent a bacterial colony with varying
level of antibiotic resistance. Explain this process by responding to the prompts
below:
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a. Explain what occurs within the first circle, “Before antibiotics” that leads to
the results in the second circle, “After antibiotics”.
b. Explain what happens within the second circle, “After antibiotics”, that
leads to the third circle, “Final population”.
c. Describe the final population of bacteria.
3. The illustration below shows a type of virus that infects bacterial cells.
a. What is the name for this type of virus?
b. Label the parts of the virus shown on the illustration.
c. Describe the sequence of events that occur within the lytic cycle from
attachment of the virus to a bacterial cell through the release of new
viruses.
4. There are four phases to bacterial growth, as shown in the graph below.
http://www.smccd.edu/accounts/case/biol230/growth
For each of the four phases labeled on the graph above, describe the following:
a. the activities of the bacterial cells
b. the state of the resources available to the bacteria
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5. An experiment was performed to determine the effectiveness of various
antibiotics on a particular species of bacteria. The plating results are shown
below.
http://loudoun.nvcc.edu/vetonline/vet132/micro/microbiology_unit_lesson5.htm
Use the results shown on the image above in responding to the prompts below:
a. Two disks, C and E, have zones of inhibition. Explain what this result
indicates and why these circles are clear.
b. The bacteria cells surrounding disk A grew at a rapid rate once they were
plated onto the agar. This area of the plate began with 100 bacterial cells.
This species of bacteria has a generation time of 60 minutes. The plates
were placed into a 37oC incubator for 48 hours. When the plates were
removed and viewed, approximately how many bacterial cells had grown
around disk A?
Prokaryotes
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Answer Key
1. Prokaryotes are organized into bacteria and archaea.
2. Antibiotics kill bacteria in your body. Some of these bacteria are necessary for
the proper digestion of food, probiotics help augment the loss of the helpful
bacteria in your body.
3. Extremophiles are archaeans that live in extreme physical environments.
4. Archaea
5. The genetic portfolio and gene expression process of archaeans is more similar
to that of eukaryotes than bacteria.
6. Bacteria aid our bodies in digestion, and some helpful bacteria attack harmful
forms of bacteria.
7. Bacteria are extremely small, and they evolved much earlier than eukaryotes and
have had millions of more years to develop greater levels of diversity.
8. The fact that archaeans live in environments with extreme physical conditions.
9. Until recently, archaeans were considered to be more closely related to bacteria
than eukaryotes. New scientific evidence and techniques refuted this idea. As
scientists discover new evidence and develop new techniques, former ideas are
challenged and refined.
10. Strep means that the bacteria are organized into a line, coccus is spherical
shape
11. Bacteria have cell walls and often times capsules. Animal cells have neither of
these.
12. The one with the capsule. The capsule works very similar to the gel coat of the
Tylenol.
13. The bacteria would move in response to the presence of a chemical. A flagellum
would likely be involved in the movement.
14. Fimbriae are like the burrs on a seed or like Velcro, anything that aids in external
attachment to a foreign surface.
15. Pili are used to transfer genetic information from one bacterium to another.
16. The peptidoglycan is found in the cell wall.
17. The “F” factor allows for the existence of a sex pilus which would allow the
bacterium to spread its genetic material to another bacterium.
18. Staph means the bacteria forms clusters, coccus means spherical.
19. Cellulose and peptidoglycan are both tough carbohydrates used in the
construction of cell walls.
20. The bacterium would move in a reaction to light.
21. While both are stiff extensions extending from the exterior surface of a bacterium,
fimbriae are used for attachment, sex pili are used for transferring genetic
material.
22. The diversity would not be as great in the gene pool in the absence of pili.
23. The bacterium that carries the R plasmid would be more likely to survive and
exhibit resistance to an antibiotic than bacteria lacking the plasmid.
24. The locus of a gene would indicate where on a chromosome the gene was
located.
25. Binary fission
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26. The bacterial chromosome is circular and double stranded, so during replication
when the chromosome is split, the bubble appears.
27. Binary fission is asexual reproduction. It is the splitting of an individual
bacterium.
28. An operon is a system of molecules that is used to regulate gene expression.
29. Operons allow prokaryotes to regulate their gene expression in response to
changes in the environment. Environmental response is one of the
characteristics of living organisms.
30. The lac operon allows the prokaryote to save energy by not producing lactase in
the absence of lactose. Since lactase is basically useless in the absence of
lactose, the organism saves energy by not producing it when it is not needed.
31. Lactose
32. Tryptophan is the repressor in this operon.
33. Since this is a repressible operon, tryptophan deactivates the transcription of the
gene that would initiate its production in the organism.
34. The operator essentially activates or deactivates the operon, the promoter is the
region of DNA that attracts the enzymes to begin transcription and the gene is
the segment of DNA that codes for a protein that is affected by the operons
activation or deactivation.
35. Mutualism. Both organisms are benefited from this relationship.
36. Parasitism. The bacteria is positively affected, your body is negatively affected.
37. These bacteria will benefit each other by utilizing different substances produced
by each type of bacteria. These bacteria will be more likely to live longer and
reproduce more frequently than bacteria living in isolation.
38. Prokaryotic chromosomes are singular and circular.
39. Two. There is one replication fork at each end of the replication bubble.
40. Transcription occurs in the cytoplasm.
41. Repressors bind to the operator region of a gene and turn off transcription.
42. Both actions conserve energy. Turning off the lights conserves electricity, the lac
operon conserves cellular energy by not unnecessarily producing lactase.
43. Inducible operons are usually off and can be turned on, repressible operons are
usually on and can be turned off.
44. The body does not have to unnecessarily produce the amino acid tryptophan if it
is already present in the environment.
45. Symbiosis is an interaction between two organisms providing benefit to at least
one organism.
46. Parasitism.
47. The bacteria have access to products produced by each other that they may not
be able to produce on their own.
48. Prokaryotes are more numerous and reproduce more quickly than other
organisms, which will naturally create a higher mutation rate, leading to
increased genetic diversity.
49. Griffith proved that a non-virulent strain of bacteria could gain virulence simply
through exposure to dead individuals of a virulent strain.
50. Sexual reproduction involves donation of genetic material from two individuals to
create a genetically unique offspring.
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51. Viruses transfer genetic information from one bacterium to another as it
incorporates host DNA and infects future bacteria.
52. No. The virus needs to inject its genetic material into a host cell and utilize the
cellular machinery of the host cell in order to reproduce.
53. Viruses inject their genetic material into a cell, and the cell copies the viral DNA
and produces the protein coat for the viral ‘offspring.’
54. The lytic cycle results in immediate host cell death, whereas in the lysogenic
cycle the viral DNA is incorporated but may remain dormant for an undetermined
amount of time.
55. Temperate phages may use the lytic or lysogenic cycle.
56. Host range is the number of hosts that a specific virus may successfully infect. A
virus may only successfully reproduce in one of these host cells.
57. Transformation allows a prokaryote to assimilate genetic material from another
prokaryote, thus increasing genetic diversity.
58. Sex pili allow a bacterium to transfer genetic material to another bacterium.
59. No. Viruses do not satisfy the requirements of living organisms. They do not
have cells, no metabolism, cannot reproduce on their own.
60. Viruses inject their DNA/RNA into a host cell and use the organelles of the host
cell to replicate their DNA/RNA and produce new viruses.
61. Since viruses require other cells in order to reproduce, and viruses only use
specific host cells, it makes sense that they would evolve in relationship with their
host cells.
62. The lysogenic cycle allows a virus to incorporate its genetic material into the host
cell, allowing it to replicate and be transferred to new host cells without becoming
activated and destroying the host cell.
63. Obligate- require other cells; Intracellular- within cells; Parasite- benefits while
negatively affecting host cell
64. Find DNA (DNA sequencer) – Cut DNA (restriction enzymes) – Isolate DNA (gel
electrophoresis) – Amplification of DNA (PCR) – Create Plasmid (restriction
enzymes) – Insert into host – Collect Protein Product
65. Gel electrophoresis separates segments of DNA by length that have been cut
using restriction. By applying a charge to the gel, the segments of DNA move
from one end to the other, and the lighter segments, which contain fewer bases,
will move further than the longer, heavier regions
66. The universality of DNA allows it to be transferred between different species of
organisms and still be read by the new organisms. If the structure of DNA
changed between species, exchanging DNA between species would not be
possible
67. PCR allows DNA to produced at a much more rapid rate than could be
conducted using natural processes
68. The segments that have moved the furthest away from the starting point contain
the fewest bases, the segments closest to the start contain the most bases
69. Genetic engineering would be much more complicated, because segments of
DNA would not be compatible between two organisms of a different species.
Genes of interest would have to be translated, and then replicated using the DNA
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format of a different organism. This would be a much more complicated and time
consuming process.
1. Question 1
a. the lac operon is an inducible operon; the trp operon is a repressible
operon.
b. Repressible operons are ones that are typically “on”.
c. Inducible operons are ones that are typically “off”.
d. A repressible operon is typically on. When the concentration of a corepressor becomes high enough, it attaches to a repressor. The repressor
is then able to attach to the DNA at a site called the operator. When the
repressor is in this position, the gene cannot be transcribed, disrupting the
production of the protein. Therefore, the protein that was initially steadily
produced, is not being produced.
2. Question 2
a. Before antibiotics there is a somewhat diverse population of bacteria, with
regard to antibiotic resistance. The bacteria range from low resistance to
high resistance. Antibiotics are introduced which changes the bacterial
population.
b. After antibiotics shows the bacteria remaining after antibiotics have been
introduced into the environment. The bacteria that had low to moderate
antibiotic resistance are no longer in the environment. Only those bacteria
that are highly resistant have survived. The remaining highly resistant
bacteria survive and reproduce leading to “final population”.
c. The population that once existed has been entirely changed to bacteria
with high antibiotic resistance. If the same antibiotics were introduced into
this new environment it would likely have very little effect on these
bacteria; they would continue to grow and increase in number.
3. Question 3
a. Bacteriophage
b. From top to bottom: Head; Sheath; Tail; Base
c. 1. A virus particle attaches to a host cell. 2. The particle releases its
genetic instructions into the host cell. 3. The injected genetic material
recruits the host cell's enzymes. 4. The enzymes make parts for more new
virus particles. 5. The new particles assemble the parts into new viruses.
6. The new particles break free from the host cell.
4. Question 4
a. Lag phase: bacteria are reproducing and growing in number; Exponential
growth phase: bacteria are rapidly dividing, doubling with each
generation; Stationary phase: bacteria are reproducing at a sustainable
level. No increase in population overall; Logarithmic decline: more
bacteria are dying that are being replaced. Population numbers rapidly
decreasing
b. Lag phase: more resources than current population can utilize;
Exponential growth: abundant resources supporting the population
increase; Stationary phase: resources become limiting; Logarithmic
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decline: resources decreasing with each generation; unable to support
any population growth, bacteria dying
5. Question 5
a. Zones of inhibition indicate that no bacteria grew in these areas, in this
case around disks A and E. The disks were dipped into antibiotics.
Therefore, the bacteria plated onto the agar are susceptible to antibiotics
C and E and not susceptible to antibiotics A, B, or D. The circles around
C and E are clear because there is no bacterial growth.
b. 2.81 x 1016 estimated bacterial cells
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