Chapter 7: DNA Structure and Replication Quiz
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Questions and Answers

What is the key difference between the S (smooth) and R (rough) strains of Pneumococcus identified by Frederick Griffith?

  • The S strain is genetically stable, while the R strain can undergo genetic mutations.
  • The S strain is more resistant to antibiotics compared to the R strain.
  • The S strain has a polysaccharide capsule, while the R strain lacks this capsule.
  • The S strain is virulent and causes fatal pneumonia, while the R strain is avirulent and does not cause illness. (correct)

    • Which of the following was the key finding from Griffith's transformation experiment?

  • Avirulent R strains of Pneumococcus could be transformed into virulent S strains.
  • The transforming principle was likely a component of the polysaccharide capsule or a compound required for capsule synthesis.
  • Genetic material could be transferred between bacterial cells, leading to changes in phenotype.
  • All of the above were key findings from Griffith's transformation experiment. (correct)

    • Why did geneticists in the 1940s favor proteins as the genetic material rather than DNA?

  • Proteins were thought to be more stable and less prone to mutations than DNA.
  • DNA had not yet been identified as the hereditary molecule at that time.
  • Proteins were believed to have a more complex structure that could better encode genetic information.
  • Proteins were known to be more abundant and diverse in cells compared to DNA. (correct)

    • What was the key finding from the Hershey-Chase experiment using bacteriophage T2?

    <p>Bacteriophage T2 injects its DNA into the bacterial host cell during infection.</p> Signup and view all the answers

    What is the difference between a nucleoside and a nucleotide?

    <p>A nucleoside contains a nitrogenous base and a pentose sugar, while a nucleotide also contains a phosphate group.</p> Signup and view all the answers

    What are Chargaff's rules of base composition in DNA?

    <p>Chargaff's rules state that the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine.</p> Signup and view all the answers

    What is the role of phosphodiester bonds in the structure of DNA?

    <p>Phosphodiester bonds link the phosphate groups of adjacent nucleotides to form the DNA backbone.</p> Signup and view all the answers

    What are the four characteristics that the genetic material must exhibit?

    <p>Replicate, store information, express information, allow variation by mutation</p> Signup and view all the answers

    When were Mendel's hereditary principles rediscovered?

    <p>1900</p> Signup and view all the answers

    Who independently described the parallels between chromosome partitioning into gametes and the inheritance of genes?

    <p>Walter Sutton and Theodor Boveri</p> Signup and view all the answers

    In what year was DNA localized to chromosomes and made a candidate for the hereditary material?

    <p>1923</p> Signup and view all the answers

    Why were both proteins and RNA also considered candidates for the hereditary material?

    <p>Due to their presence in chromosomes</p> Signup and view all the answers

    Which criteria must a molecule meet to serve as genetic material?

    <p>Replication, storage of information, expression of information, allowance for mutation</p> Signup and view all the answers

    Why were lipids and carbohydrates also considered candidates for the hereditary material?

    <p>Due to their abundance as energy sources</p> Signup and view all the answers

    Which experimental result provided crucial data for Watson and Crick's DNA model?

    <p>Both A and B</p> Signup and view all the answers

    Which of the following statements about DNA is correct according to the information provided?

    <p>All of the above</p> Signup and view all the answers

    What did Rosalind Franklin's X-ray diffraction analysis reveal about the structure of DNA?

    <p>DNA has a 3.4-angstrom periodicity, characteristic of a helical structure</p> Signup and view all the answers

    According to the Watson and Crick model, what is the structure of DNA?

    <p>A double helix with anti-parallel strands connected by base pairing</p> Signup and view all the answers

    What did James Watson and Francis Crick receive for their DNA model?

    <p>The Nobel Prize in Chemistry in 1962</p> Signup and view all the answers

    Which of the following statements about DNA is NOT supported by the information provided?

    <p>DNA is a circular molecule</p> Signup and view all the answers

    Who was the British biophysicist and X-ray crystallographer whose experimental work contributed to the discovery of DNA's structure?

    <p>Rosalind Franklin</p> Signup and view all the answers

    How many hydrogen bonds are formed between adenine (A) and thymine (T) in DNA base pairing?

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

    Which type of bond is present between guanine (G) and cytosine (C) in DNA base pairing?

    <p>Hydrogen bond</p> Signup and view all the answers

    In the structure of DNA, what makes up the backbone of the molecule?

    <p>Sugar and phosphate</p> Signup and view all the answers

    Which scientist(s) proposed the DNA double helix structure?

    <p>Watson and Crick</p> Signup and view all the answers

    What experiment helped in establishing that DNA is the genetic material?

    <p>Hershey-Chase experiment</p> Signup and view all the answers

    In Chargaff's rules of base composition, what is the ratio of adenine (A) to thymine (T)?

    <p>$1:1$</p> Signup and view all the answers

    Which direction do DNA strands run in, as indicated by the notation 5’-3’?

    <p>-5' to -3'</p> Signup and view all the answers

    What provides complementarity to the two strands of DNA?

    <p>$G-C$ base pairing</p> Signup and view all the answers

    Which type of bond is responsible for providing chemical stability to the DNA helix?

    <p>$Hydrogen$ bond</p> Signup and view all the answers

    Study Notes

    Griffith's Transformation Experiment

    • Frederick Griffith (1927) showed that avirulent strains of Streptococcus pneumoniae could be transformed to virulence
    • He speculated that the transforming principle could be part of the polysaccharide capsule or a compound required for capsule synthesis

    Avery, MacLeod, and McCarty's Experiment

    • Demonstrated that DNA is the genetic material (1944)
    • Used Streptococcus pneumoniae to show that DNA is the transforming principle

    Hershey and Chase Experiment

    • Used Escherichia coli and bacteriophage T2 to show that DNA enters the bacterial cell during infection and directs viral reproduction (1952)
    • Demonstrated that DNA, not protein, is the genetic material

    Composition and Structure of DNA

    • Nucleotides are the building blocks of DNA
    • Nucleotides consist of a nitrogenous base, pentose sugar, and phosphate group
    • DNA contains deoxyribose, while RNA contains ribose sugar

    Nucleosides and Nucleotides

    • Nucleoside: a nitrogenous base and pentose sugar
    • Nucleotide: a nucleoside with a phosphate group added
    • Mono-, di-, and triphosphates: nucleotides with one, two, or three phosphate groups added

    Phosphodiester Bonds

    • Nucleotides are linked by phosphodiester bonds between the phosphate group at the C-5' position and the OH group at the C-3' position

    Erwin Chargaff's Rules of Base Composition

    • A = T, and G = C
    • The amount of pyrimidine nucleotides (T+C) equals the amount of purine nucleotides (A+G)

    Watson and Crick's Model

    • Proposed structure of DNA as a double helix (1953)
    • Two anti-parallel strands connected by base pairing, with stacked nitrogenous bases

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    Test your knowledge on topics like the structure and replication of DNA, evidence supporting DNA as the genetic material, and the chemistry essential to DNA structure. Explore the criteria for a molecule to serve as genetic material and the rediscovery of Mendel's work in genetics.

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