Questions and Answers
What is the genetic material in the majority of organisms?
DNA
DNA is composed of nucleotides, which include phosphate, sugar, and a __________ base.
nitrogenous
What are the three characteristics that genetic material must have?
Most scientists initially believed that DNA was the source of inheritance.
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In Fred Griffith's experiment, what was the virulent strain of Streptococcus pneumoniae called?
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What term did Griffith use to describe the transmitted substance that transformed R cells into S cells?
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What did Avery, MacLeod & McCarty aim to identify in their experiment?
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Which bacteriophage was used in the Hershey & Chase experiment?
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What did the results of Experiment 1 in Hershey & Chase's study confirm?
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The results of Hershey & Chase's Experiment 2 showed the presence of 35S in the new phage.
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What was the conclusion of Gierer & Schramm's experiment with TMV?
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Study Notes
DNA as Genetic Material
- DNA is the primary genetic material in most organisms; some viruses use RNA.
- Nucleotides consist of phosphate, sugar, and nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
- DNA structure: right-handed double helix with antiparallel strands and complementary base pairing.
- DNA has directional properties: 5’ to 3’.
Characteristics Required for Genetic Material
- Must store stable information.
- Must replicate accurately to ensure progeny resembles parent.
- Must have the potential for variation to facilitate evolution.
Historical Context: Search for Genetic Material
- Initial belief placed heredity factors in the nucleus, with many scientists leaning towards proteins as the source of inheritance.
- Skepticism regarding DNA's role due to its simpler composition (only 4 nucleotide types compared to complex proteins).
- Prevailing view held that proteins within chromatin were responsible for heredity until the mid-20th century.
Fred Griffith Experiment (1928)
- Focused on Streptococcus pneumoniae infection patterns in mice.
- S-strain: smooth, virulent due to polysaccharide capsule; resistant to immune system.
- R-strain: rough, avirulent; easily destroyed by the immune system.
- Analyzed variations of strains; found that heat-killed S-strain transformed R-strain to S-strain, naming this the 'transforming principle'.
Avery, MacLeod & McCarty Experiment (1944)
- Repeated Griffith's work by isolating and purifying the 'transforming principle'.
- Showed that the heat-killed S-strains could chemically transform R-strains into S-strains.
Hershey & Chase Experiment (1953)
- Resolved the debate about genetic material by using T2 bacteriophage, which contains only DNA and protein.
- Bacteriophage infects E. coli, directing the host cell to create new phage.
- Experiment involved labeling DNA with 32P and protein with 35S to track genetic material transfer.
- Two experiments conducted:
- First Experiment: Blended mixture of infected bacteria and isolated supernatant, confirming DNA entered cells, establishing it as genetic material.
- Second Experiment: After allowing phage reproduction, only 32P (DNA) was found in offspring, supporting DNA as the hereditary substance.
Gierer & Schramm Experiment (1956)
- Purified RNA from Tobacco Mosaic Virus (TMV).
- Injected TMV RNA into tobacco leaves, causing lesions.
- Digestion of TMV RNA with RNase led to no lesions, concluding RNA serves as genetic material in TMV.
Fraenkel-Conrat & Singer Experiment (1957)
- Isolated two TMV strains with differing coat proteins.
- Analyzed the impact of the coat protein on the virus's infectivity and genetic properties.
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Description
This quiz covers Week 1 of the Introductory Genetics course, focusing on the structure and function of DNA as the genetic material. You'll explore the components of nucleotides, the double helix structure, and the importance of complementary base pairing. Test your understanding of how DNA's directionality influences genetic information.
