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Questions and Answers
What model of DNA replication was supported by the experiments of Meselson and Stahl?
What model of DNA replication was supported by the experiments of Meselson and Stahl?
What are the complementary base pairs in DNA as explained by Chargaff's rules?
What are the complementary base pairs in DNA as explained by Chargaff's rules?
How many base pairs are there per turn in the DNA double helix?
How many base pairs are there per turn in the DNA double helix?
What is the origin of replication in prokaryotes?
What is the origin of replication in prokaryotes?
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What structure forms at each origin of replication during DNA replication?
What structure forms at each origin of replication during DNA replication?
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What did Griffith's experiment with Streptococcus pneumoniae demonstrate?
What did Griffith's experiment with Streptococcus pneumoniae demonstrate?
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What was the key finding of Hershey and Chase's experiment in 1952?
What was the key finding of Hershey and Chase's experiment in 1952?
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What circumstantial evidence supports the idea that DNA is the genetic material in eukaryotic cells?
What circumstantial evidence supports the idea that DNA is the genetic material in eukaryotic cells?
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What did Chargaff's 1947 experiment reveal about DNA?
What did Chargaff's 1947 experiment reveal about DNA?
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Which of the following statements about transformation is true?
Which of the following statements about transformation is true?
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What is a significant characteristic of bacteriophages in the context of genetic material?
What is a significant characteristic of bacteriophages in the context of genetic material?
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What structural feature of DNA did Watson and Crick discover?
What structural feature of DNA did Watson and Crick discover?
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Why was there doubt about DNA being the genetic material?
Why was there doubt about DNA being the genetic material?
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Study Notes
Molecular Basis of Inheritance
- Evidence that DNA is genetic material
- Mendel discovered heritable factors
- Morgan identified genes on chromosomes
- Search for the genetic material began
Griffith's Transformation Experiment
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1928: Griffith experimented with Streptococcus pneumoniae
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Smooth cells (with capsules): pathogenic
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Rough cells (without capsules): not pathogenic
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Heat-killed smooth cells: not pathogenic
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Heat-killed smooth cells + rough cells: pathogenic and produce live smooth cells
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Conclusion: Genetic material transferred from smooth to rough cells
Transforming Principle
- Transforming Principle: What was transferred from smooth to rough cells?
- Protein and DNA are components of chromosomes
- Protein is denatured by heat
- DNA is the probable transforming material
Bacteriophages and DNA
- Evidence that DNA is the genetic material came from studying bacteriophages (phages)
- Phage DNA programs bacterial cells
- Hershey and Chase 1952 experiment confirmed that DNA is genetic material in bacteriophages
Evidence for DNA in Eukaryotes
- DNA content doubles before mitosis
- During cell division, double DNA is divided equally between daughter cells
- Diploid cells have twice the DNA compared to haploid cells
- DNA composition varies between different species
Chargaff's Rules
- 1947: Chargaff used paper chromatography to study DNA base composition in different species
- Adenine (A) + Thymine (T) = Guanine (G) + Cytosine (C)
- Base composition varies between species, but A=T and G=C
Watson and Crick's Double Helix Model
- Watson and Crick discovered DNA's double helix structure
- Based on evidence from others like Hershey/Chase and Chargaff
- DNA is a double helix of two strands in antiparallel orientation. A-T and G-C
DNA Replication
- DNA replicates by using itself as a template
- Two strands separate, acting as templates forming two new complementary strands.
- Replication follows the semiconservative model. Each new DNA has one old and one new strand
DNA Replication Overview
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DNA replication requires enzymes and proteins
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Extremely rapid in prokaryotes and slower in eukaryotes
- Accuracy is high in both cases
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Origin of replication (multiple origins in eukaryotes, single in prokaryotes)
Replication of DNA
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Strand separation is driven by enzymes called helicases
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Topoisomerase reduces strain caused by strand separation
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Synthesis happens in 5' to 3' direction
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Leading strand: continuous synthesis
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Lagging strand: discontinuous synthesis, replicated in short fragments (Okazaki fragments).
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Okazaki fragments are joined by the enzyme DNA ligase
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Primase creates primers to start replication
Replication Elongation
- DNA replication proceeds with enzymes and their functions, including polymerase and primase.
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Description
Explore the key experiments and discoveries that identified DNA as the genetic material. This quiz covers Griffith's transformation experiment, the role of bacteriophages, and the contributions of scientists like Mendel and Morgan. Test your understanding of the concepts pivotal to molecular genetics.
