Lab 6
Microbiology
Learning Objectives
Describe the structure of a typical bacterium.
Characterize the value of a Gram stain as a differential stain.
Describe the cellular replication process for bacteria.
Relate the development of bacterial resistance to the principles of transformation,
transduction, and conjugation.
Characterize sporulation.
Describe the general structure of a virus.
Compare the viral replication processes for DNA and RNA viruses.
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Activity 1: Bacteria
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1. Functionally, how are pili different from flagella?
2. A bacillus has what shape?
3. Why can the lipopolysaccharide in the outer membrane of Gram-negative
bacteria be dangerous to humans?
4. How many chromosomes are present in a bacterium?
5. What are plasmids?
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Activity 1: Bacteria (continued)
Suggest a hypothesis for the above image:
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Activity 2: The Gram Stain
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1. How many bacterial cells become purple with exposure to crystal violet stain?
2. What would happen if someone forgot the iodine step in a Gram stain?
3. What allows bacteria to be decolorized by an alcohol solution?
4. Why is the Gram stain called a differential staining procedure?
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Activity 3: Binary Fission
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1. Describe bacterial multiplication?
2. What is a transverse septum?
3. If binary fission occurs every 15 minutes, beginning with a single bacterium, how
many bacterial organisms will be present after 6 hours?
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Activity 4: Transformation
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1. In transformation, what is taken into the bacterial cell?
2. Where did the genetic information likely come from in the process of
transformation?
3. What structure changed inside the transformed cell?
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Activity 5: Transduction
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1. What is a bacteriophage?
2. How does the bacteriophage attach the bacterium?
3. What do viral enzymes do to the host cell chromosome?
4. How do the bacteriophages leave the host cell?
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Activity 6: Conjugation
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1. How does conjugation differ from both transduction and transformation?
2. What is the conjugation bridge built to transfer the genetic information?
3. What does it mean when a cell is F+?
4. Can a F- cell transfer information to a F+ cell? Why?
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Activity 7: Sporulation
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1. Why is sporulation important to a bacterial cell?
2. What protects the spore when the mother cell disintegrates?
3. What is the preferred environment of Clostridium tetani?
4. Do spores release bacterial toxins? Why or why not?
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Activity 8: Viruses
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1. Luis had a very painful coldsore on his upper lip. Earlier that semester he had used
a topical cream containing polymyxin to treat an infected cut on his hand. At that
time, he had read in his microbiology textbook that polymyxin is an antibiotic that
disrupts cell membranes. He applied some polymyxin cream to his coldsore daily,
but obtained no relief. Why did this treatment fail?
2. You are taking an introductory microbiology class and you cannot afford to get
sick. An exam is scheduled for next week and you really need to be able to study.
You tell your friend that you think you are coming down with a cold. Your friend
says that he has some antibiotics left over from an illness he had a year ago. He
would be glad to give them to you for you to take. Should you take them?
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Activity 9: Viruses
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1. What is the structure of a polio virus if it is a non-enveloped virus?
2. What does it mean if a polio virus is a (+) sense RNA virus?
3. How are capsid proteins produced by the host cell?
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Activity 10: HIV Virus
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1. Describe the structure of the HIV virus.
2. What is unique about the cells destroyed by the HIV virus?
3. For the HIV virus to enter the cell, what is the lock and what is the key?
4. What is the role of reverse transcriptase in HIV virus replication?
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