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Questions and Answers
What was the main finding of Frederick Griffith's experiment in 1928?
What component did Macleod, McCarty, and Avery identify as responsible for transforming rough cells into smooth cells?
In Griffith's experiment, what was the outcome when mice were injected with heat-killed smooth strain bacteria?
Which of the following enzymes was used to determine the transforming activity in Avery's experiments?
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What type of virus did Hershey and Chase study in their experiments?
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What characteristic differentiates the pathogenic strain of pneumococci bacteria from the non-pathogenic strain?
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What was the primary aim of Hershey and Chase's experiment?
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What observation was made when rough strain bacteria were injected alongside heat-killed smooth strain bacteria?
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What is the primary purpose of phage infecting a bacterium?
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Which radioactive element was used to label the DNA of phages in the first experiment?
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What did the researchers find in the second experiment regarding the radioactive sulfur tracer?
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What is one of the three important properties that a molecule carrying genetic information must have?
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What did Hershey receive the Nobel Prize for?
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What are the main types of nitrogen bases found in DNA?
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In the context of molecular biology, what is now often viewed as the central dogma?
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What key aspect of DNA structure assists in the understanding of Mendelian genetics?
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What primarily encodes the information content of DNA?
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How does the structure of DNA contribute to the accuracy of replication?
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What effect can a single base pair change have on a gene?
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What is the estimated mutation frequency for a given gene in humans?
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What could significantly elevate the mutation rate in DNA?
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What type of variations do mutations usually cause within a species?
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Which form of DNA is primarily represented in organisms?
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How many genes are estimated to be present in humans?
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Which nucleotide base pairs with adenine in DNA?
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What type of bond forms between adjacent nucleotides in a single strand of DNA?
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What is the significance of the major and minor grooves found in DNA?
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What is the physical structure of standard DNA found in vivo?
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In DNA replication, what does the term 'semi-conservative' refer to?
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How many bases per turn does a typical DNA helix contain?
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Which form of DNA is associated with increased instability due to its unique structural configuration?
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Which statement about the hydrogen bonds between DNA bases is true?
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Study Notes
DNA: The Molecule of Life
- Discovery: DNA was identified in the 1940s and 50s through a series of experiments. Frederick Griffith's 1928 experiment demonstrated that genetic information could be transferred between bacteria using heat-killed pathogenic (smooth colony-forming) bacteria and live non-pathogenic (rough colony-forming) bacteria.
- Transforming Principle: Macleod, McCarty, and Avery (1944) followed up on Griffith's work and showed that DNA was the active agent in transferring genetic information, specifically the gene for the polysaccharide coat responsible for virulence.
- Hershey-Chase Experiment (1952): This landmark experiment confirmed that DNA and not protein carries genetic information. They used radioactive isotopes of phosphorus (present in DNA) and sulfur (present in proteins) to label the T2 phage. The results showed that DNA was injected into the bacteria, proving it was the genetic material responsible for phage replication.
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DNA Structure (Watson and Crick, 1953): The structure of DNA was determined using X-ray diffraction techniques. It consists of two antiparallel strands of nucleotides linked by hydrogen bonds between complementary bases.
- Adenine (A) pairs with Thymine (T) through two hydrogen bonds.
- Guanine (G) pairs with Cytosine (C) through three hydrogen bonds.
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DNA Properties:
- Replication: DNA can be faithfully replicated, ensuring that genetic information is accurately passed on to daughter cells during cell division.
- Information Storage: The sequence of bases in DNA carries genetic information.
- Variation: Changes in the base sequence, known as mutations, provide the basis for genetic diversity and evolution.
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DNA Organization:
- Single Strand Polymer: A single strand of DNA has a specific 5' to 3' polarity determined by the direction of phosphodiester bonds.
- Double Helix: The two strands of DNA are twisted into a double helix, forming major and minor grooves due to the asymmetry in base pairing. This structure promotes protein interaction.
- Biological Forms: DNA exists in various forms, with the standard form in living organisms being the B-form. A-form and Z-form also exist, with different structural characteristics and unknown physiological significance.
- Length: DNA molecules can be very long, extending for centimeters in human chromosomes.
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DNA Replication:
- Semi-conservative Replication: During replication, the double helix unwinds, and each strand serves as a template for the synthesis of a new complementary strand, resulting in two identical DNA molecules, each containing one original and one new strand.
- Mechanism: The process is guided by base pairing rules, ensuring accurate copying.
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Genetic Information:
- Limited Variations: DNA's structure explains how variations in the genetic information, like different eye colors in humans, arise through mutations, which can occur at a rate of 1/10,000 to 1/million per gene.
- Environmental Factors: Mutations can be induced by environmental factors such as radiation or chemicals that damage DNA.
Central Dogma of Molecular Biology
- Classic View: DNA is transcribed into RNA, which is then translated into protein.
- Current View: The role of RNA has expanded, recognizing its ability to catalyze reactions. This has led to an updated view of the central dogma: RNA can be transcribed into DNA (reverse transcription), and both DNA and RNA can produce proteins through translation.
- Significance of RNA: The discovery of catalytic RNA, a novel function, challenges the classic view and highlights the complexity of molecular biology.
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Description
Explore the fascinating journey of DNA discovery and its pivotal role in genetics. Learn about key experiments, including those by Griffith, Avery, and Hershey-Chase that established DNA as the genetic material. This quiz covers the milestones that shaped our understanding of molecular biology.
