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Ch. 5 - Genetics
Norman-McKay- Microbiology: Basic and Clinical Principles 2nd Edition
Norman-McKay2nd EditionMicrobiology: Basic and Clinical PrinciplesISBN: 9780137661619Not the one you use?Change textbook
All textbooksNorman-McKay 2nd EditionCh. 5 - GeneticsProblem 21
Chapter 5, Problem 21

In Griffith's classical experiments on transformation, which of the following scenarios led to a dead mouse? Select all that apply.
a. Infecting the mouse with a living strain of S. pneumoniae that makes a capsule
b. Infecting the mouse with a heat-killed strain of S. pneumoniae that makes a capsule
c. Infecting the mouse with a heat-killed strain of S. pneumoniae that makes a capsule and a living strain of S. pneumoniae that cannot make a capsule
d. Infecting the mouse with a living strain of S. pneumoniae that cannot make a capsule

Verified step by step guidance
1
Step 1: Understand the key difference between the two strains of S. pneumoniae used in Griffith's experiment: the encapsulated (smooth, S) strain is virulent and causes death in mice, while the non-encapsulated (rough, R) strain is non-virulent and does not cause death.
Step 2: Analyze option (a): Infecting the mouse with a living encapsulated (S) strain. Since this strain is virulent due to its capsule, it will cause disease and lead to the death of the mouse.
Step 3: Analyze option (b): Infecting the mouse with a heat-killed encapsulated (S) strain. Heat-killed bacteria are not alive and cannot cause disease, so the mouse will survive.
Step 4: Analyze option (c): Infecting the mouse with a mixture of heat-killed encapsulated (S) strain and living non-encapsulated (R) strain. The heat-killed S strain can release genetic material that transforms the living R strain into a virulent form, causing the mouse to die.
Step 5: Analyze option (d): Infecting the mouse with a living non-encapsulated (R) strain. Since this strain lacks the capsule and is non-virulent, the mouse will survive.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Griffith's Experiment and Bacterial Transformation

Griffith's experiment demonstrated that non-virulent bacteria could acquire virulence by taking up genetic material from heat-killed virulent bacteria. This process, called transformation, showed that DNA carries genetic information, allowing harmless bacteria to become deadly.
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The Griffith Experiment

Role of the Bacterial Capsule in Virulence

The capsule is a polysaccharide layer surrounding some bacteria, like S. pneumoniae, which protects them from the host immune system. Strains with capsules are virulent and cause disease, while those without capsules are typically non-virulent and do not kill the host.
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Heat-Killed Bacteria and Their Effect on Infection

Heat-killed bacteria are dead and cannot cause infection by themselves. However, their genetic material can be taken up by living non-virulent bacteria, enabling transformation. In Griffith's experiment, only the combination of heat-killed virulent and live non-virulent bacteria led to a lethal infection.
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Related Practice
Textbook Question

Protein synthesis occurs in two main stages: ___________ and ___________.

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Textbook Question

Select all the true statements about repressible operons:

a. By default they are on until turned off.

b. An example is the lactose operon.

c. An example is the arginine operon.

d. A repressor must bind to the operator in order for the operon to be turned off.

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Textbook Question

Cells that can be transformed are said to be ___________.

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Textbook Question

Use the genetic code table in the chapter and the DNA sequence below to answer the following questions:

3'-TACATAAAATAATGGCGTTCTATT-5'

a. What would the mRNA sequence be, based on the provided DNA sequence?

b. What would the corresponding polypeptide sequence be for this DNA sequence?

c. What tRNA anticodon loop would correspond to the third codon of the mRNA?

d. What would the mRNA and polypeptide sequences be if the second adenine in the DNA was deleted?

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Textbook Question

Which of the following is produced by transcription?

a. mRNA

b. Protein

c. DNA

d. None of the above

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Textbook Question

Quorum sensing helps cells _______.

a. mutate

b. form biofilms

c. carry out transduction

d. copy their DNA

e. perform conjugation

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