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Chapter 10: Problem 19

A student mixes some heat-killed type IIS Streptococcus pneumoniae bacteria with live type IIR bacteria and injects the mixture into a mouse. The mouse develops pneumonia and dies. The student recovers some type IIS bacteria from the dead mouse. If this is the only experiment conducted by the student, has the student demonstrated that transformation has taken place? What other explanations might explain the presence of the type IIS bacteria in the dead mouse?

Short Answer

Expert verified
Without additional controls, the conclusion of transformation isn't definitive due to alternate explanations like contamination or revived bacteria.

Step by step solution

01

Understanding Transformation

Transformation is a genetic process where one bacterium takes up DNA from its environment. In this experiment, the student introduced heat-killed type IIS bacteria into a mouse along with live type IIR bacteria. The dead mouse had live type IIS bacteria, suggesting that genetic material from the dead IIS bacteria transformed the live IIR bacteria into the virulent IIS type.
02

Analyzing Other Possibilities

One alternative explanation could be contamination; perhaps the inoculation of the mouse was accidentally contaminated with live type IIS bacteria. Another possibility is that the transformation did not occur, and instead, some heat-killed type IIS were incompletely killed and somehow revived in the mouse.
03

Considering Experimental Controls

To strengthen the conclusion that transformation occurred, the student should include controls such as: (1) injecting mice with heat-killed IIS bacteria alone to ensure they do not recover, (2) injecting with live IIR to confirm they do not become lethal, and (3) ensuring no live IIS are present in the starting materials before injection. These controls would help rule out errors or contamination.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Genetic Transformation
Genetic transformation is a fascinating biological process where bacteria obtain genetic material from their environment, often from other bacterial cells. This naturally occurring phenomenon can lead to significant changes in the properties of the recipient bacterium.
  • In the exercise, type IIR bacteria likely received genetic material from the dead type IIS bacteria, which was heat-killed before injection.
  • Once the type IIR bacteria incorporated this new genetic material, they transformed into virulent type IIS bacteria, causing illness in the host, a mouse.
Understanding the mechanics of this process helps in thinking about how genes can be exchanged in microbial communities.
This exchange can affect bacterial traits, including antibiotic resistance or virulence. Genetic transformation is fundamental not just in bacterial evolution but also in biotechnology, where it's used in genetic engineering.
Streptococcus pneumoniae
Streptococcus pneumoniae is a bacterium known for causing serious illnesses such as pneumonia. It is particularly noteworthy in the study of genetic transformation.
Here's why:
  • S. pneumoniae exists in different strains, such as the virulent type IIS and the non-virulent type IIR.
  • In experiments, scientists have observed how these strains can change character when interacting with each other's genetic material.
In the exercise, the transition of S. pneumoniae from a harmless to a virulent type demonstrates the potential for significant bacterial transformation.
This understanding is crucial for vaccine development and for combatting bacterial diseases effectively.
Experimental Controls
When conducting experiments, especially complex ones like genetic transformation, experimental controls are crucial for validating results. They help determine whether the observed phenomena are genuinely related to the experimental conditions.
  • In our exercise, controls such as administering heat-killed IIS bacteria alone would verify if they are actually dead and non-promotive of disease.
  • Injecting with live IIR bacteria should show whether they remain harmless, highlighting any effect of IIS genetic material involvement.
  • Checking for contamination by ensuring no live IIS bacteria are initially present can prevent misleading results.
These controls establish a framework to confidently claim that a transformation has truly occurred.
Contamination
Contamination is a key consideration in scientific experiments and can easily lead to incorrect conclusions if not adequately managed.
In the context of the student experiment:
  • Contamination can occur if live type IIS bacteria accidentally mix with the experiment's bacteria samples, resulting in misleading outcomes.
  • Preventing contamination involves rigorous sterile techniques and careful handling to ensure no unwanted organisms or elements are introduced.
By recognizing potential sources of contamination and controlling them, researchers can be more certain about the reliability and accuracy of their experimental results.
This is essential for maintaining scientific integrity and advancing our understanding of genetic transformation processes.

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Most popular questions from this chapter

Match the researchers (a-j) with the discoveries listed. a. Kossel f. Hershey and Chase b. Fraenkel-Conrat g. Avery, MacLeod, and McCarty c. Wat son and Crick h. Griffith d. Levene i. Franklin and Wilkins e. Miescher j. Chargaff _____ Took X-ray diffraction pictures used in constructing the structure of DNA. _____ Determined that DNA contains nitrogenous bases. _____ Identified DNA as the genetic material in bacteriophage. _____ Discovered regularity in the ratios of different bases in DNA. _____ Determined that DNA is responsible for transformation in bacteria. _____ Worked out the helical structure of DNA by building models. _____ Discovered that DNA consists of repeating nudeotides. _____ Determined that DNA is acidic and high in phosphorous. _____ Conducted experiments showing that RNA can serve as the genetic material in some viruses. _____ Demonstrated that heat-killed material from bacteria can genetically transform live bacteria.

What are some of the important genetic implications of the DNA structure?

The introduction to this chapter, about the sequencing of 4000 -year-old DNA, emphasizes DNA's extreme stability. What aspects of DNA's structure contribute to the stability of the molecule? Why is RNA less stable than DNA?

Scientists have reportedly isolated short fragments of DNA from fossilized dinosaur bones hundreds of millions of years old. The technique used to isolate this DNA is the polymerase chain reaction, which is capable of amplifying very small amounts of DNA a millionfold (see Chapter 19 ). Critics have claimed that the DNA isolated from dinosaur bones is not purely of ancient origin but instead has been contaminated by DNA from present-day organisms such as bacteria, mold, or humans. What precautions, analyses, and control experiments could be carried out to ensure that DNA recovered from fossils is truly of ancient origin?

A B-DNA molecule has 1 million nucleotide pairs. How many complete turns are there in this molecule?
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