DNA: The Molecule of Life
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Questions and Answers

What was the main finding of Frederick Griffith's experiment in 1928?

  • Heat-killed smooth strain bacteria can cause disease.
  • Rough strain bacteria can transform into smooth strain. (correct)
  • Only smooth strain bacteria cause disease.
  • Pathogenicity is determined by the environment.
  • What component did Macleod, McCarty, and Avery identify as responsible for transforming rough cells into smooth cells?

  • RNA
  • DNA (correct)
  • Protein
  • Polysaccharides
  • In Griffith's experiment, what was the outcome when mice were injected with heat-killed smooth strain bacteria?

  • The mice developed immunity.
  • The mice exhibited unusual behavior.
  • The mice developed pneumonia.
  • The mice survived without illness. (correct)
  • Which of the following enzymes was used to determine the transforming activity in Avery's experiments?

    <p>DNases</p> Signup and view all the answers

    What type of virus did Hershey and Chase study in their experiments?

    <p>Bacteriophage</p> Signup and view all the answers

    What characteristic differentiates the pathogenic strain of pneumococci bacteria from the non-pathogenic strain?

    <p>Presence of a polysaccharide coat</p> Signup and view all the answers

    What was the primary aim of Hershey and Chase's experiment?

    <p>To determine whether DNA or protein carries genetic information.</p> Signup and view all the answers

    What observation was made when rough strain bacteria were injected alongside heat-killed smooth strain bacteria?

    <p>The mice died and smooth strain bacteria were recovered.</p> Signup and view all the answers

    What is the primary purpose of phage infecting a bacterium?

    <p>To insert its own DNA into the bacterium</p> Signup and view all the answers

    Which radioactive element was used to label the DNA of phages in the first experiment?

    <p>Phosphorus-32</p> Signup and view all the answers

    What did the researchers find in the second experiment regarding the radioactive sulfur tracer?

    <p>It was found in the protein shells</p> Signup and view all the answers

    What is one of the three important properties that a molecule carrying genetic information must have?

    <p>It must be capable of faithful replication</p> Signup and view all the answers

    What did Hershey receive the Nobel Prize for?

    <p>Discoveries concerning the genetic structure of viruses</p> Signup and view all the answers

    What are the main types of nitrogen bases found in DNA?

    <p>Purines and pyrimidines</p> Signup and view all the answers

    In the context of molecular biology, what is now often viewed as the central dogma?

    <p>RNA → DNA → RNA → Protein</p> Signup and view all the answers

    What key aspect of DNA structure assists in the understanding of Mendelian genetics?

    <p>Chromosome behavior</p> Signup and view all the answers

    What primarily encodes the information content of DNA?

    <p>The linear arrangement of base pairs</p> Signup and view all the answers

    How does the structure of DNA contribute to the accuracy of replication?

    <p>It maintains linearity in base pair arrangement</p> Signup and view all the answers

    What effect can a single base pair change have on a gene?

    <p>It can vary from having no effect to completely altering function</p> Signup and view all the answers

    What is the estimated mutation frequency for a given gene in humans?

    <p>1 in 10,000 to 1 in a million</p> Signup and view all the answers

    What could significantly elevate the mutation rate in DNA?

    <p>Chemicals or radiation that damage DNA</p> Signup and view all the answers

    What type of variations do mutations usually cause within a species?

    <p>Subtle changes leading to diverse traits</p> Signup and view all the answers

    Which form of DNA is primarily represented in organisms?

    <p>B DNA</p> Signup and view all the answers

    How many genes are estimated to be present in humans?

    <p>20,000-25,000</p> Signup and view all the answers

    Which nucleotide base pairs with adenine in DNA?

    <p>Thymine</p> Signup and view all the answers

    What type of bond forms between adjacent nucleotides in a single strand of DNA?

    <p>Covalent phosphodiester bonds</p> Signup and view all the answers

    What is the significance of the major and minor grooves found in DNA?

    <p>They facilitate transcription factor recognition</p> Signup and view all the answers

    What is the physical structure of standard DNA found in vivo?

    <p>B form DNA</p> Signup and view all the answers

    In DNA replication, what does the term 'semi-conservative' refer to?

    <p>Each new DNA molecule contains one old strand and one new strand</p> Signup and view all the answers

    How many bases per turn does a typical DNA helix contain?

    <p>10 bases</p> Signup and view all the answers

    Which form of DNA is associated with increased instability due to its unique structural configuration?

    <p>Z form DNA</p> Signup and view all the answers

    Which statement about the hydrogen bonds between DNA bases is true?

    <p>G-C pairs form three hydrogen bonds</p> Signup and view all the answers

    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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.

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