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Questions and Answers
What is the term used to describe the pairing of adenine with thymine and guanine with cytosine in DNA?
What is the term used to describe the pairing of adenine with thymine and guanine with cytosine in DNA?
Which feature of DNA is described as having different widths with distinct structural roles?
Which feature of DNA is described as having different widths with distinct structural roles?
How does DNA replication ensure that each daughter cell has an identical copy of DNA?
How does DNA replication ensure that each daughter cell has an identical copy of DNA?
Which enzyme is primarily responsible for adding nucleotides to a growing chain during DNA replication?
Which enzyme is primarily responsible for adding nucleotides to a growing chain during DNA replication?
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What characteristic of DNA allows it to undergo mutation?
What characteristic of DNA allows it to undergo mutation?
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What structural characteristic defines the orientation of the two strands of DNA?
What structural characteristic defines the orientation of the two strands of DNA?
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Which experiment identified DNA as the transformation factor?
Which experiment identified DNA as the transformation factor?
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What was the primary focus of Griffith’s experiment?
What was the primary focus of Griffith’s experiment?
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What method did Hershey and Chase use to differentiate between DNA and proteins?
What method did Hershey and Chase use to differentiate between DNA and proteins?
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What conclusion can be drawn if a phage containing both DNA and RNA were used in the Hershey and Chase experiment?
What conclusion can be drawn if a phage containing both DNA and RNA were used in the Hershey and Chase experiment?
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What role does DnaA play in the replication initiation process?
What role does DnaA play in the replication initiation process?
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What type of virus was used in the Hershey and Chase experiment?
What type of virus was used in the Hershey and Chase experiment?
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Which of the following is NOT an essential characteristic of hereditary material?
Which of the following is NOT an essential characteristic of hereditary material?
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How does the replication of the lagging strand differ from that of the leading strand?
How does the replication of the lagging strand differ from that of the leading strand?
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Which of the following statements accurately describes DNA polymerase?
Which of the following statements accurately describes DNA polymerase?
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Avery's experiment destroyed which of the following components to determine its role in transformation?
Avery's experiment destroyed which of the following components to determine its role in transformation?
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What is the primary function of primase during DNA replication?
What is the primary function of primase during DNA replication?
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What is the consensus sequence used for in the replication initiation process?
What is the consensus sequence used for in the replication initiation process?
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What is the result of DNA replication as observed in bacteria?
What is the result of DNA replication as observed in bacteria?
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Which experimental technique was used to distinguish between heavy and light nitrogen in the Meselson-Stahl experiment?
Which experimental technique was used to distinguish between heavy and light nitrogen in the Meselson-Stahl experiment?
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What characterizes the directionality of DNA replication in bacteria?
What characterizes the directionality of DNA replication in bacteria?
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How fast can E.coli DNA polymerase replicate DNA?
How fast can E.coli DNA polymerase replicate DNA?
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What was the primary evidence supporting bidirectional replication of DNA?
What was the primary evidence supporting bidirectional replication of DNA?
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How many origins of replication can be found in the human genome?
How many origins of replication can be found in the human genome?
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What would be observed in the Meselson and Stahl experiment if DNA replication was conservative?
What would be observed in the Meselson and Stahl experiment if DNA replication was conservative?
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What is a characteristic feature of DNA replication in eukaryotic organisms?
What is a characteristic feature of DNA replication in eukaryotic organisms?
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What is the role of DNA polymerase I in replication?
What is the role of DNA polymerase I in replication?
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What is the primary function of DNA ligase during DNA replication?
What is the primary function of DNA ligase during DNA replication?
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How does the proofreading ability of DNA polymerases work?
How does the proofreading ability of DNA polymerases work?
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What is the function of telomerase in eukaryotic cells?
What is the function of telomerase in eukaryotic cells?
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Why do differentiated somatic cells have limited lifespans?
Why do differentiated somatic cells have limited lifespans?
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What is a consequence of telomere shortening in cells?
What is a consequence of telomere shortening in cells?
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What happens to the 3'-OH end of a DNA strand during proofreading?
What happens to the 3'-OH end of a DNA strand during proofreading?
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What condition is associated with dyskeratosis congenita?
What condition is associated with dyskeratosis congenita?
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Study Notes
DNA as the Hereditary Molecule of Life
- Essential characteristics of hereditary material: Found in the nucleus, stable, sufficiently complex, accurately replicates itself, and mutable.
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Foundational experiments:
- Griffith's experiment discovered the 'transformation factor' in Pneumococcus.
- Avery's experiment identified DNA specifically as the 'transformation factor'.
- Hershey and Chase confirmed DNA is the hereditary material using bacteriophage T2.
Griffith’s Experiment
- Identified two strains of Pneumococcus: S strain (virulent) and R strain (non-virulent).
- Each strain exhibited four antigenic types (I, II, III, IV).
- Suggested the existence of a 'transformation factor'.
Avery’s Experiment
- Used the same S and R strains as Griffith.
- Systematically destroyed lipids, proteins, RNA, or DNA to determine what was needed for transformation.
Hershey and Chase Experiment
- Utilized bacteriophage proteins labeled with radioactive sulfur (35S) and DNA labeled with phosphorus (32P).
- Traced radioactive labels during infection to confirm that DNA, not protein, is the genetic material.
The DNA Double Helix
- Structure consists of two complementary, antiparallel strands.
- A pairs with T, and G pairs with C; this base pairing ensures genetic fidelity.
- Characterized by an axis of helical symmetry, a conserved diameter, and major and minor grooves.
DNA Replication Process
- Semiconservative and bidirectional replication: each parental strand serves as a template for a new strand.
- In bacterial DNA replication, it proceeds bidirectionally from a single origin of replication.
Meselson-Stahl Experiment
- Used cesium chloride gradient ultracentrifugation to distinguish DNA with heavy nitrogen (15N) from light nitrogen (14N).
- Provided evidence supporting the semiconservative mechanism of DNA replication.
Replication Origins and Directionality
- E. coli replication initiates at specific consensus sequences (oriC) and progresses bidirectionally.
- Eukaryotic genomes possess thousands of origins, with the human genome containing approximately 10,000 origins.
Mechanism of DNA Replication in Bacteria
- Initiation: DnaA binds to oriC, bends DNA, and breaks hydrogen bonds.
- Unwinding: Helicase (DnaB) unwinds DNA strands while DnaC transports DnaB.
- Nucleotide Addition: DNA polymerase requires an existing 3’ OH to add nucleotides. RNA primers synthesized by primase initiate replication.
Leading and Lagging Strand Synthesis
- Leading strand synthesized continuously in the same direction as the replication fork.
- Lagging strand synthesized discontinuously using Okazaki fragments in the opposite direction.
RNA Primer Removal and Fragment Ligation
- DNA polymerase I removes RNA primers and fills in gaps with DNA.
- DNA ligase seals the nicks between DNA segments.
Topoisomerase Function
- Prevents supercoiling by catalyzing controlled cleavage and rejoining of DNA strands.
Proofreading and Error Correction
- DNA replication errors occur once per billion nucleotides due to proofreading by DNA polymerase with 3’-to-5’ exonuclease activity.
- Mismatched base pairs are corrected by removing incorrect nucleotides.
Telomeres and Aging
- Telomeres are repetitive DNA sequences at the ends of linear chromosomes that cannot be fully replicated.
- Telomerase, a protein-RNA complex, synthesizes telomeres, active primarily in germ-line and some stem cells.
- Differentiated somatic cells lack telomerase activity leading to limited lifespan and the Hayflick limit (50-70 divisions).
Applications: Telomeres, Aging, and Cancer
- Dyskeratosis congenita is a condition linked to defective telomerase function.
- Abnormal reactivation of telomerase is associated with cancer proliferation.
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Description
This quiz covers DNA as the hereditary molecule of life, focusing on its essential characteristics and foundational experiments. Review key concepts such as the stability, complexity, and replication of DNA. Test your understanding of Chapter 7 and its implications in genetics.