Week 7: DNA Structure and Replication Quiz
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Questions and Answers

What is the role of initiator proteins in DNA replication?

  • They help in the binding of DNA polymerase to the template strand.
  • They seal the nicks in the newly formed DNA strands.
  • They aid in the synthesis of nucleotides.
  • They recognize specific sequences and open the double helix. (correct)

    • What describes the model of DNA replication that involves each parent strand serving as a template for a new strand?

  • Conservative model
  • Semiconservative model (correct)
  • Dispersive model
  • Hybrid model

    • How do replication bubbles contribute to DNA replication?

  • They prevent the synthesis of new daughter strands.
  • They form the basis for chromosome separation.
  • They enable simultaneous replication in both directions. (correct)
  • They allow RNA synthesis to occur during replication.

    • Which of the following statements about origins of replication is true?

    <p>Replication starts at specific sites where DNA strands separate.</p> Signup and view all the answers

    What occurs at the replication fork?

    <p>The double helix is unwound and template strands are exposed.</p> Signup and view all the answers

    What two types of proteins work together to unzip the DNA double helix?

    <p>DNA helicases and single-strand DNA-binding proteins.</p> Signup and view all the answers

    In which model of DNA replication do the two parental strands remain together after replication?

    <p>Conservative model</p> Signup and view all the answers

    How many strands of DNA are typically involved in the replication process?

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

    What happens when replication bubbles fuse?

    <p>Synthesis of the daughter strands is complete.</p> Signup and view all the answers

    What type of model suggests that each daughter DNA molecule contains both old and newly synthesized DNA?

    <p>Dispersive model</p> Signup and view all the answers

    Why is the unzipping of DNA important during replication?

    <p>It provides access for incoming nucleoside triphosphates to form base pairs.</p> Signup and view all the answers

    Where does DNA replication begin in eukaryotic cells?

    <p>At multiple sites along each chromosome.</p> Signup and view all the answers

    What is the primary function of the DNA replication process?

    <p>To copy the genetic information for cell division.</p> Signup and view all the answers

    What distinguishes the structure of bacterial and eukaryotic chromosomes with respect to replication origins?

    <p>Eukaryotic chromosomes can have hundreds of origins of replication.</p> Signup and view all the answers

    What is a replication machine responsible for in the DNA replication process?

    <p>Carrying out specific functions during DNA replication.</p> Signup and view all the answers

    Which statement best describes the complementary nature of DNA strands in replication?

    <p>Each strand can serve as a template for synthesis based on pairing rules.</p> Signup and view all the answers

    What is the main challenge associated with the replication of linear DNA in eukaryotic chromosomes?

    <p>DNA polymerases cannot replicate or repair a specific region at the ends.</p> Signup and view all the answers

    Which DNA polymerase is responsible for the initial synthesis of the leading strand in eukaryotic cells?

    <p>DNA pol ε</p> Signup and view all the answers

    How are Okazaki fragments on the lagging strand of DNA joined together?

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

    During DNA replication, the antiparallel nature of DNA affects which of the following processes?

    <p>Leading strand synthesis is continuous while lagging strand synthesis is fragmented.</p> Signup and view all the answers

    What is the role of DNA pol α in eukaryotic DNA replication?

    <p>It initiates the synthesis of both leading and lagging strands.</p> Signup and view all the answers

    What is the primary function of primase in DNA replication?

    <p>To initiate RNA synthesis on the DNA template</p> Signup and view all the answers

    During DNA elongation, what forms the bond between the 3' end of the growing DNA strand and the incoming nucleotide?

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

    Which molecule provides the energy necessary for the polymerization of nucleotides during DNA synthesis?

    <p>Deoxyribonucleoside triphosphate</p> Signup and view all the answers

    How many different DNA polymerases have been discovered in eukaryotic cells?

    <p>15</p> Signup and view all the answers

    Which part of the RNA primer does the new DNA strand begin to elongate from?

    <p>3' end</p> Signup and view all the answers

    What is released during the linkage of a nucleotide monomer to the DNA chain?

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

    What identifies eukaryotic DNA polymerases in terms of nomenclature?

    <p>Greek letters</p> Signup and view all the answers

    What is the role of pyrophosphate in DNA replication?

    <p>To provide energy for the reaction</p> Signup and view all the answers

    What is the primary role of DNA in cells?

    <p>To encode hereditary information</p> Signup and view all the answers

    During which phase of the cell-division cycle does DNA replication occur in eukaryotic cells?

    <p>S phase</p> Signup and view all the answers

    What is a key feature of the DNA structure represented in the diagram?

    <p>It contains phosphodiester bonds and hydrogen bonds</p> Signup and view all the answers

    Which component is found at the 5' end of a DNA strand?

    <p>A phosphate group</p> Signup and view all the answers

    Which nitrogenous base pairs with adenine in DNA?

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

    What structural component is essential for the formation of a nucleosome?

    <p>Histone proteins</p> Signup and view all the answers

    What characteristic of DNA contributes to its stability and structural integrity?

    <p>Phosphodiester linkages</p> Signup and view all the answers

    What would most likely happen if DNA replication did not occur during the S phase?

    <p>Cells would have an incomplete set of genetic instructions</p> Signup and view all the answers

    What type of bond forms between complementary bases in DNA?

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

    Which of the following is NOT a function of DNA?

    <p>Catalyzing metabolic reactions</p> Signup and view all the answers

    Why can't an Okazaki fragment's RNA primer be replaced with DNA after removal?

    <p>There is no 3’ end available for nucleotide addition.</p> Signup and view all the answers

    What happens to eukaryotic chromosomal DNA with each round of replication?

    <p>It gets shorter with each round of replication.</p> Signup and view all the answers

    What is the primary function of telomeres?

    <p>To protect genes from erosion during replication.</p> Signup and view all the answers

    What characteristic is true about the nucleotide sequences of telomeres?

    <p>They are composed of repetitive short nucleotide sequences.</p> Signup and view all the answers

    What specific sequence is often repeated in human telomeres?

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

    What is the role of telomerase in relation to telomeres?

    <p>To maintain and extend telomere length.</p> Signup and view all the answers

    Which of the following best describes the effect of each replication cycle on daughter DNA molecules?

    <p>They become progressively shorter.</p> Signup and view all the answers

    What consequence does the absence of a 3’ end have during DNA replication?

    <p>It limits nucleotide addition, resulting in shorter DNA.</p> Signup and view all the answers

    What is the primary function of helicases during DNA replication?

    <p>To separate double helix strands at replication forks</p> Signup and view all the answers

    How do single-strand binding proteins contribute to DNA replication?

    <p>By preventing strands from re-forming base pairs</p> Signup and view all the answers

    What role does topoisomerase play during DNA replication?

    <p>To relieve tension created by unwinding</p> Signup and view all the answers

    Which statement accurately describes DNA polymerase's ability to initiate synthesis?

    <p>It can only add nucleotides to an existing chain</p> Signup and view all the answers

    What type of molecule serves as a primer for DNA polymerase during replication?

    <p>An RNA chain synthesized by primase</p> Signup and view all the answers

    What happens when the helicase unzips the DNA double helix?

    <p>It creates tension that can break the DNA</p> Signup and view all the answers

    How does the sliding clamp assist DNA polymerase during replication?

    <p>It keeps DNA polymerase attached to the template strand</p> Signup and view all the answers

    Which enzyme is responsible for creating the RNA primer necessary for DNA synthesis?

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

    What is the key outcome of the semiconservative model of DNA replication?

    <p>Each daughter molecule contains one old strand and one newly synthesized strand.</p> Signup and view all the answers

    What defines the locations where DNA replication begins in eukaryotic cells?

    <p>Origins of replication</p> Signup and view all the answers

    Which model of DNA replication suggests that the two parental strands remain together after replication?

    <p>Conservative model</p> Signup and view all the answers

    In the context of DNA replication, how do eukaryotic chromosomes differ from bacterial genomes?

    <p>Eukaryotic chromosomes may possess multiple origins of replication.</p> Signup and view all the answers

    What characteristic of the dispersive model of DNA replication distinguishes it from the other models?

    <p>Daughter molecules are hybrid, containing both old and new segments.</p> Signup and view all the answers

    Which of the following accurately describes the behavior of parental strands during the semiconservative replication process?

    <p>They act as templates for new strand synthesis and remain intact.</p> Signup and view all the answers

    What best describes the parental DNA molecule at the start of replication?

    <p>It remains double-stranded and unwinds into two separate strands.</p> Signup and view all the answers

    Which model of DNA replication posits that the parental strands separate entirely during replication?

    <p>Semiconservative model</p> Signup and view all the answers

    What initiates the formation of a new DNA strand during replication?

    <p>The completion of the RNA primer</p> Signup and view all the answers

    Which component is essential for the formation of a phosphodiester bond during DNA elongation?

    <p>The high-energy phosphate bond of deoxyribonucleoside triphosphate</p> Signup and view all the answers

    What is the primary function of the RNA primer in DNA replication?

    <p>To provide a free 3' end for DNA polymerase</p> Signup and view all the answers

    Which statement accurately describes the role of deoxyribonucleoside triphosphate in DNA replication?

    <p>It serves as the building block of the DNA polymer.</p> Signup and view all the answers

    What is released as a byproduct during the formation of a new DNA strand?

    <p>A molecule of pyrophosphate</p> Signup and view all the answers

    How many different DNA polymerases have been discovered in eukaryotic organisms?

    <p>Exactly 15 types</p> Signup and view all the answers

    Which best distinguishes eukaryotic DNA polymerases from bacterial ones?

    <p>Eukaryotic DNA polymerases have multiple types indicated by Greek letters.</p> Signup and view all the answers

    What is a significant feature of the nucleotide sequence in telomeres?

    <p>Telomeres are composed of repeating sequences.</p> Signup and view all the answers

    During which specific phase of the cell-division cycle is DNA replication in most eukaryotic cells carried out?

    <p>S phase</p> Signup and view all the answers

    What type of bond is formed between the phosphate group of one nucleotide and the hydroxyl group of another during DNA synthesis?

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

    Which structural end of a DNA strand does the synthesis of a new DNA strand begin from?

    <p>3' end</p> Signup and view all the answers

    What role does the DNA program play in the development of different traits?

    <p>It directs the development of various traits.</p> Signup and view all the answers

    Which of the following correctly states the relationship between DNA structure and its stability?

    <p>The double-helix structure confers stability and integrity.</p> Signup and view all the answers

    What is a consequence of DNA replication not occurring at the appropriate time in the cell cycle?

    <p>Potential genetic instability</p> Signup and view all the answers

    Which nitrogenous base does thymine pair with in a DNA molecule?

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

    What feature distinguishes the roles of nucleotides in DNA synthesis?

    <p>They act as energy carriers.</p> Signup and view all the answers

    What primary component regulates the encoding of hereditary information in cells?

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

    Which element of DNA architecture constrains the directionality of replication?

    <p>Antiparallel strands</p> Signup and view all the answers

    What prevents the addition of DNA nucleotides following the removal of an Okazaki fragment's RNA primer?

    <p>The unavailability of a 3' hydroxyl end</p> Signup and view all the answers

    How do telomeres protect eukaryotic chromosomal DNA?

    <p>By serving as a buffer zone to shield genes from erosion</p> Signup and view all the answers

    What is the primary reason eukaryotic chromosomal DNA becomes shorter with each replication cycle?

    <p>The inability to fully replicate the ends of linear chromosomes</p> Signup and view all the answers

    What is the typical structure of the nucleotide sequences found in telomeres?

    <p>Short, repetitive nucleotide sequences without genes</p> Signup and view all the answers

    What is the specific nucleotide sequence repeated in human telomeres?

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

    Which of the following statements about telomerase is true?

    <p>It prevents DNA degradation by synthesizing telomeric DNA.</p> Signup and view all the answers

    In what way does the removal of RNA primers impact the lagging strand during DNA replication?

    <p>It creates a gap without a 3' end for new nucleotide addition.</p> Signup and view all the answers

    What type of DNA sequences are often termed as 'buffer zones' in eukaryotic chromosomal DNA?

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

    What is the main role of telomerase in eukaryotic germ cells?

    <p>It lengthens telomeres to restore their original length.</p> Signup and view all the answers

    What is a significant consequence of telomerase activation in cancer cells?

    <p>It allows cancer cells to grow indefinitely.</p> Signup and view all the answers

    How does telomere length relate to colorectal cancer progression?

    <p>TERT increases with disease progression in most cases.</p> Signup and view all the answers

    What factors can accelerate telomere erosion in colorectal cancer?

    <p>Alterations in genes involved in CRC carcinogenesis.</p> Signup and view all the answers

    Which of the following markers shows promise for monitoring colorectal cancer progression?

    <p>Plasma TERT mRNA levels.</p> Signup and view all the answers

    What role do genes like APC and MSH2 play in colorectal cancer?

    <p>They are involved in DNA repair and tumor suppression.</p> Signup and view all the answers

    What is the significance of telomerase activity in somatic cells?

    <p>It has a role in aging and cancer in somatic tissues.</p> Signup and view all the answers

    Which statement reflects the current understanding of telomerase as a prognostic factor in colorectal cancer?

    <p>Most studies suggest it is a useful prognostic factor under debate.</p> Signup and view all the answers

    Study Notes

    DNA and DNA Replication

    • DNA is the genetic material, encoding hereditary information and directing the development of traits.
    • DNA replication in eukaryotes occurs during the S phase (synthesis phase) of the cell cycle.
    • DNA strands are complementary; each acts as a template for a new strand during replication.
    • The parent DNA molecule unwinds to create two new daughter strands via base-pairing rules.
    • DNA replication is semiconservative, each new daughter molecule has one old strand and one new strand.

    DNA Structure

    • DNA is a double helix.
    • The double helix has a sugar-phosphate backbone.
    • Bases pair together: Adenine with Thymine, Cytosine with Guanine, held by hydrogen bonds.

    DNA Replication: Origins of Replication

    • Replication starts at specific sites called origins of replication.
    • Eukaryotic chromosomes have hundreds/thousands of origins.
    • Bacterial genomes are circular, with a single origin.
    • Initiator proteins recognize origin sites, separating DNA strands to form a replication bubble.
    • Replication proceeds in both directions from the origin.
    • A replication machine, formed by proteins with specific functions, moves along the DNA at the replication fork.
    • The replication fork is the Y-shaped region where parental strands are unwound.

    DNA Replication: Challenges and Solutions

    • Unzipping a helical molecule creates tension.
    • Single-strand binding proteins (SSBPs) bind to the separated strands, keeping them from re-pairing.
    • Topoisomerase relieves the tension by breaking, swiveling, and rejoining DNA strands.

    DNA Replication: Replication Machinery

    • An additional replication protein, called a sliding clamp, keeps DNA polymerase firmly attached to the template strand.
    • DNA polymerases catalyze the addition of nucleotides to the 3' end of the growing strand.
    • The polymerization reaction uses the energy from incoming deoxyribonucleoside triphosphates, forming phosphodiester bonds.
    • Specific DNA polymerases (eukaryotic use Greek letters; bacterial use Roman numerals) are involved in replication, repair, and other processes.

    DNA Replication: Initiation

    • DNA polymerases cannot initiate synthesis; they only add nucleotides to an existing chain.
    • An RNA primer, synthesized by primase, provides the starting point for the new DNA strand.
    • Primers are short stretches of RNA (~5-10 nucleotides).
    • The new DNA strand always starts from the 3' end of the RNA primer.

    DNA Replication: Elongation

    • DNA polymerase adds nucleotides to the 3' end of the growing strand in a 5' to 3' direction.
    • Nucleotides enter the reaction as deoxyribonucleoside triphosphates, providing energy for the polymerization reaction.
    • Leading strand is synthesized continuously; lagging strand is synthesized in fragments (Okazaki fragments).

    DNA Replication: Antiparallel Elongation

    • DNA polymerases add nucleotides only to the 3' end of a growing strand.
    • Along one template strand, the leading strand DNA polymerase synthesizes a complementary strand continuously, moving toward the replication fork.
    • The lagging strand is synthesized in fragments (Okazaki fragments) in the direction away from the replication fork.

    Replicating the Ends of DNA Molecules

    • Linear DNA molecules have ends that cannot be completely replicated by DNA polymerases (no 3' end to add to).
    • Telomeres are repetitive nucleotide sequences at the ends of linear chromosomes, acting as protective caps.
    • Telomerase is an enzyme that maintains telomere length by adding repeats to the 3' end of the lagging strand.
    • Telomerase is active in germ cells, but usually inactive in somatic cells.

    Clinical Correlation: Colorectal Cancer

    • Colorectal cancer (CRC) is a significant cause of cancer-related deaths.
    • Telomere length and telomerase activity are potential prognostic factors in CRC.
    • Factors such as cell proliferation and alterations in genes like APC and MSH2 may be involved in CRC carcinogenesis and telomere shortening/telomerase activity.

    References & Further Reading

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    DNA and DNA Replication PDF

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    Test your knowledge on DNA's structure and replication mechanisms, including its role as genetic material and the processes involved during the S phase of the cell cycle. Explore how DNA strands act as templates, the significance of complementary base pairing, and the initiation of replication.

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