Molecular Biology of the Gene - Chapter 12
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Questions and Answers

What is the main function of nucleotide excision repair?

  • Adds telomeres to the ends of DNA molecules
  • Replicates the ends of DNA molecules
  • Removes damaged stretches of DNA (correct)
  • Prevents the shortening of DNA molecules

    • The error rate of DNA replication is zero due to efficient proofreading and repair mechanisms.

    False (B)

    What are mutations and how are they significant in evolution?

    Mutations are permanent changes in DNA sequences that can be passed on to offspring. They introduce genetic variation, which is the raw material for natural selection, leading to the evolution of new species.

    The special nucleotide sequences at the ends of eukaryotic chromosomal DNA molecules are called ______.

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

    Match the following terms with their corresponding descriptions:

    <p>DNA polymerase = An enzyme that adds nucleotides to a growing DNA strand Telomere = A protective cap at the end of a chromosome Mutation = A permanent change in the DNA sequence Nucleotide excision repair = A mechanism to remove and replace damaged DNA segments</p> Signup and view all the answers

    What type of sugar is found in the nucleotide dATP?

    <p>Deoxyribose (B)</p> Signup and view all the answers

    DNA polymerase adds nucleotides only to the free 5' end of a growing strand.

    <p>False (B)</p> Signup and view all the answers

    What is the name given to the short segments of DNA synthesized on the lagging strand?

    <p>Okazaki fragments</p> Signup and view all the answers

    The enzyme ____ joins the Okazaki fragments together on the lagging strand.

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

    What is the primary function of the DNA replication machine?

    <p>To synthesize new DNA strands (D)</p> Signup and view all the answers

    DNA polymerase can only add nucleotides in the 3' to 5' direction.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the process by which DNA polymerase corrects any mistakes made during DNA replication?

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

    Which of these components of T2 phage enters an E. coli cell during infection?

    <p>DNA (A)</p> Signup and view all the answers

    Erwin Chargaff's research proved that DNA is the genetic material.

    <p>False (B)</p> Signup and view all the answers

    What technique did Maurice Wilkins and Rosalind Franklin use to study the structure of DNA?

    <p>X-ray crystallography</p> Signup and view all the answers

    According to Chargaff's rules, the number of adenine (A) bases in DNA is equal to the number of ______ bases.

    <p>thymine (T)</p> Signup and view all the answers

    Match the scientists with their contributions to understanding DNA.

    <p>Alfred Hershey and Martha Chase = Proved that DNA is the genetic material Erwin Chargaff = Discovered the base pairing rules in DNA Maurice Wilkins and Rosalind Franklin = Used X-ray crystallography to study DNA structure James Watson = Proposed the double helix model of DNA structure</p> Signup and view all the answers

    What did Rosalind Franklin conclude about the structure of DNA?

    <p>There were two outer sugar-phosphate backbones. (A), The nitrogenous bases were paired in the molecule's interior. (C)</p> Signup and view all the answers

    Watson and Crick initially believed that adenine paired with thymine and guanine paired with cytosine.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the process by which DNA is copied?

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

    The two strands of DNA are ______ , meaning they run in opposite directions.

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

    Which of the following is NOT a competing model of DNA replication?

    <p>Transformative model (B)</p> Signup and view all the answers

    What is the significance of Chargaff's rules in the context of DNA structure?

    <p>Chargaff's rules, which state that the amount of adenine equals the amount of thymine and the amount of guanine equals the amount of cytosine, support the Watson-Crick model of DNA structure and base pairing.</p> Signup and view all the answers

    The semiconservative model of DNA replication predicts that each daughter molecule will have two old strands.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the Y-shaped region where parental DNA strands are being unwound during replication?

    <p>Replication fork (C)</p> Signup and view all the answers

    DNA polymerases require a primer to start DNA synthesis.

    <p>True (A)</p> Signup and view all the answers

    What are the two main enzymes involved in unwinding the DNA double helix during replication?

    <p>Helicases and topoisomerase</p> Signup and view all the answers

    The initial nucleotide chain in DNA replication is a short ______ primer.

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

    Match the following enzymes with their functions in DNA replication:

    <p>DNA polymerase = Synthesizes new DNA strands Primase = Synthesizes short RNA primers Helicase = Unwinds the DNA double helix Topoisomerase = Relieves the strain of twisting in the DNA helix</p> Signup and view all the answers

    Which of the following scientists was NOT involved in the discovery of DNA as the genetic material?

    <p>Linus Pauling (C)</p> Signup and view all the answers

    Which scientist(s) provided experimental evidence supporting the semiconservative model of DNA replication?

    <p>Meselson and Stahl (B)</p> Signup and view all the answers

    T.H. Morgan's research showed that genes are located on chromosomes.

    <p>True (A)</p> Signup and view all the answers

    Eukaryotic chromosomes have only one origin of replication.

    <p>False (B)</p> Signup and view all the answers

    What is bacteriophage?

    <p>A virus that infects bacteria.</p> Signup and view all the answers

    What is the primary function of single-strand binding proteins during DNA replication?

    <p>To stabilize the single-stranded DNA after it is unwound by helicases</p> Signup and view all the answers

    The process of ______ refers to the change in genotype and phenotype due to the assimilation of foreign DNA.

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

    Which of the following was NOT a key piece of evidence supporting DNA as the genetic material?

    <p>The presence of DNA in chromosomes (B)</p> Signup and view all the answers

    Match the following scientists with their contributions:

    <p>Frederick Griffith = Discovered transformation in bacteria Oswald Avery, Maclyn McCarty, and Colin MacLeod = Identified DNA as the transforming substance Alfred Hershey and Martha Chase = Confirmed DNA as the genetic material in viruses T.H. Morgan = Demonstrated that genes are located on chromosomes</p> Signup and view all the answers

    Why were many biologists initially skeptical about DNA being the genetic material?

    <p>Little was known about DNA's structure and function at the time.</p> Signup and view all the answers

    Viruses always contain DNA as their genetic material.

    <p>False (B)</p> Signup and view all the answers

    Flashcards

    Hershey-Chase Experiment

    An experiment demonstrating that DNA is the genetic material of T2 phage.

    DNA structure

    DNA is a polymer of nucleotides with a nitrogenous base, sugar, and phosphate.

    Chargaff’s rules

    In DNA, number of A=T and G=C; base composition varies among species.

    Erwin Chargaff

    Reported that DNA base composition varies by species, supporting DNA's role in heredity.

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    X-ray crystallography

    Technique used to study molecular structure, particularly DNA by Franklin and Wilkins.

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    double helix

    The shape of DNA, confirmed by Watson using X-ray images.

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    Nitrogenous bases

    Components of DNA that include adenine, thymine, guanine, and cytosine.

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    T2 phage

    A virus that infects E. coli used in Hershey and Chase's experiment.

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    Antiparallel Strands

    DNA strands run in opposite directions.

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    Chargaff's Rules

    In DNA, the amount of A equals T, and G equals C.

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    Base Pairing

    Specific pairing of nitrogenous bases in DNA (A with T, G with C).

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    DNA Replication

    The process of copying DNA to produce two identical DNA molecules.

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    Template Strand

    A strand of DNA that serves as a guide to synthesize a new strand.

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    Semiconservative Replication

    Each new DNA molecule consists of one old strand and one new strand.

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    Competing Replication Models

    The conservative and dispersive models differ in how DNA strands are used.

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    Nucleoside triphosphate

    Building blocks added to DNA strands during replication, providing the necessary nucleotides.

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    dATP

    A specific nucleoside triphosphate that supplies adenine to DNA and contains deoxyribose.

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    Dehydration reaction

    Process where a nucleotide joins a DNA strand, losing two phosphate groups as pyrophosphate.

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    Antiparallel structure

    Orientation of DNA strands in opposite directions, affecting replication direction.

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    Leading strand

    The DNA strand that is synthesized continuously toward the replication fork.

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    Lagging strand

    The DNA strand synthesized in segments, moving away from the replication fork in Okazaki fragments.

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    Okazaki fragments

    Short segments of DNA synthesized on the lagging strand during replication.

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    DNA polymerase

    Enzyme that adds nucleotides to a growing DNA strand and proofreads the DNA.

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    Genetic Material

    Substance that carries genetic information; DNA or RNA.

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    T.H. Morgan's Contribution

    Demonstrated that genes are located on chromosomes.

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    Transformation

    Change in genotype and phenotype due to foreign DNA.

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    Frederick Griffith

    Conducted experiments that demonstrated DNA's role in heredity.

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    Heat-killed Pathogen

    Dead bacterial cells used in Griffith's transformation experiments.

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    Bacteriophages

    Viruses that infect bacteria, used to study DNA.

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    Oswald Avery's Work

    Identified DNA as the transforming substance in Griffith's experiments.

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    Phage T2

    A type of bacteriophage used in molecular genetics studies.

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    Semiconservative Model

    A method of DNA replication where each new DNA helix contains one original and one new strand.

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    Nucleotide Excision Repair

    A DNA repair mechanism where a nuclease cuts out damaged DNA and replaces it.

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    Origins of Replication

    Specific sites on DNA where replication begins, creating a bubble.

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    Mutations

    Permanent changes in the DNA sequence that can be passed to the next generation.

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    Replication Fork

    A Y-shaped region at each end of a replication bubble where DNA strands are unwound.

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    Helicases

    Enzymes that unwind the DNA double helix at the replication forks.

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    Telomeres

    Special nucleotide sequences at the ends of eukaryotic chromosomes that protect DNA from shortening.

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    DNA Shortening

    The process where linear DNA becomes shorter after each replication due to the inability to complete 5' ends.

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    Single-strand Binding Proteins

    Proteins that stabilize and protect single-stranded DNA after unwinding.

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    Aging and Telomeres

    The connection between the shortening of telomeres and the aging process in organisms.

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    Topoisomerase

    An enzyme that alleviates strain on DNA strands during unwinding by cutting and rejoining them.

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    Primase

    An enzyme that synthesizes a short RNA primer for DNA replication to start.

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    Study Notes

    Chapter 12: Molecular Biology of the Gene - Part 1

    • DNA is the genetic material

      • Morgan's group showed genes reside on chromosomes, with DNA and protein being candidates for the genetic material
      • DNA's hereditary role was first discovered through studying bacteria and infecting viruses.
      • Griffith observed transformation (change in genotype and phenotype due to foreign DNA assimilation).
      • Avery, McCarty, and MacLeod identified the transforming substance as DNA

    • Evidence that DNA can transform bacteria

      • Frederick Griffith's 1928 research with bacteria strains (pathogenic and harmless) sparked the investigation.
      • When heat-killed pathogenic bacteria were mixed with living harmless ones, some living cells turned pathogenic (transformation).

    • Evidence that viral DNA can program cells

      • Bacteriophages (phages) are viruses that infect bacteria.
      • Phages have DNA (occasionally RNA) encased in a protein coat.
      • Phages have been key tools in molecular genetics research.
      • Hershey and Chase experiment:
        • Alfred Hershey and Martha Chase (1952) demonstrated that viral DNA (and not protein) enters the bacteria during infection, establishing that DNA is the genetic material, not protein.
        • DNA was tracked using radioactive isotopes.
      • The experiment involved phage T2.

    • Additional evidence that DNA is the genetic material.

      • DNA is a polymer of nucleotides (nitrogenous base, sugar, and phosphate group).
        • Nitrogenous bases can be adenine (A), thymine (T), guanine (G), or cytosine (C)
      • Erwin Chargaff's (1950) findings revealed species-specific DNA compositions.
      • This diversity further supported DNA as the genetic material.

    Chargaff's Rules

    • Base composition of DNA varies among species.
    • In any species, the number of A and T bases is equal, and the number of G and C bases is equal.

    Structure of DNA

    • DNA's structure was established using X-ray crystallography data, which provided crucial information about its helical structure.
      • Franklin's X-ray diffraction images were critical in determining the DNA structure.
      • Watson and Crick built a model of the double helix based on existing information, including Franklin's data and the complementary base pairing rule.

    DNA Replication and Repair

    • DNA replication ensures offspring resemble parents

      • Replication prior to mitosis ensures the faithful transmission of genetic information from a parent cell to daughter cells.
      • Watson and Crick recognized that specific base pairing suggests a copying mechanism for genetic material, thus initiating studies on DNA replication.
      • DNA replication is guided by the principle of complementarity.

    • The Basic Principle - Base Pairing to a Template Strand

      • DNA strands are complementary, acting as templates for new strand construction.
      • This results in two exact copies of the original DNA molecule.

    • Watson and Crick's Semiconservative Model

      • When DNA replicates, each daughter molecule has one old strand and one new strand

    • Experiments by Meselson and Stahl

      • Experiments with isotopes confirmed the semiconservative model,

    • DNA Replication: A Closer Look

      • DNA replication is a complex process involving multiple enzymes, remarkable for both speed and accuracy.

    • Bacterial DNA Replication Processes

      • Starts at specific origins
      • The replication fork is a region where the parental strands unwind.
        • Helicases untwist the double helix.
        • Single-strand binding proteins stabilize single-stranded DNA.
        • Topoisomerase relieves strain in the double helix by reducing it.

    • Synthesizing a new DNA strand.

      • DNA polymerases require primers (short RNA segments).
      • Primase synthesizes RNA primers.
      • Polymerases add nucleotides to the 3' end.

    • Antiparallel Elongation

      • DNA polymerases add nucleotides only to the growing strand's free 3' end.

    • Leading and Lagging Strands

      • Leading strand synthesized continuously; the lagging strand is synthesized discontinuously as Okazaki fragments.
      • DNA ligase joins the fragments.

    • DNA Replication Complex

      • Enzymes work together in a complex.
      • It may be stationary during replication.

    • Proofreading and Repairing DNA

      • DNA polymerases proofread newly made DNA.
      • Repair enzymes (e.g., in mismatch repair) correct errors that avoid proofreading.

    • DNA Damage and Repair

      • DNA can be damaged by chemical or physical agents (e.g., cigarette smoke, X-rays).
      • Nucleotide excision repair (NER) involves removing and replacing damaged stretches of DNA.

    • Replicating the Ends of DNA Molecules

      • Linear DNA chromosomes have telomeres (special nucleotide sequences at the ends) to prevent shortening during each replication.

    • Evolutionary Significance of Altered DNA Nucleotides

      • Mutations (changes in DNA) are sources of genetic variation.
      • Natural selection then acts upon these variations contributing to the emergence of new species.

    • Eukaryotic Chromosome Telomeres

      • Telomeres protect genes from erosion.

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    Biology: Molecular Biology of the Gene Chapter 16 PDF

    Description

    Explore the key concepts of molecular biology in Chapter 12, focusing on the role of DNA as the genetic material. Discover how Griffith's experiments laid the foundation for understanding bacterial transformation and the significance of bacteriophages in genetic research.

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