DNA Replication (cell cycle overview)
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Questions and Answers

Which of the following is NOT a component of a nucleotide?

  • Nitrogenous Base
  • Phosphate Group
  • Sugar
  • Amino Acid (correct)

    • DNA replication always proceeds in the 3' to 5' direction.

    False (B)

    What is the primary function of DNA polymerase?

    DNA polymerase is an enzyme that synthesizes new DNA strands by adding nucleotides to an existing strand during DNA replication.

    The enzyme _______ unwinds the DNA double helix during DNA replication.

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

    Match the following enzymes with their functions in DNA replication.

    <p>DNA Polymerase = Synthesizes new DNA strands Helicase = Unwinds DNA double helix Primase = Synthesizes RNA primers Ligase = Joins Okazaki fragments</p> Signup and view all the answers

    Which phase of the cell cycle involves the duplication of DNA?

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

    The cell cycle is only required for the growth of multicellular organisms, not for repair or reproduction.

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

    What is the primary function of the G1 phase of interphase?

    <p>Growth and preparation for DNA replication.</p> Signup and view all the answers

    During ______, the chromosomes condense and become visible.

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

    Match the following stages of mitosis with their descriptions:

    <p>Prophase = Sister chromatids are pulled apart to opposite poles Metaphase = Chromosomes condense and become visible Anaphase = Chromosomes align in the center of the cell Telophase = New nuclear membranes form around the separated chromosomes</p> Signup and view all the answers

    Which of the following is NOT a phase of interphase?

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

    The G0 phase is a resting phase where cells remain dormant indefinitely.

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

    What is the significance of DNA replication being semi-conservative?

    <p>Each new DNA molecule has one strand from the original DNA and one newly synthesized strand.</p> Signup and view all the answers

    During ______, the cell’s cytoplasm divides, creating two separate daughter cells.

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

    Which of the following accurately describes the structure of DNA?

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

    Which DNA replication model was proven correct by the Meselson-Stahl experiment?

    <p>Semi-Conservative Model (B)</p> Signup and view all the answers

    DNA polymerase can add nucleotides to both the 5' and 3' ends of a DNA strand.

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

    What is the name of the Y-shaped structure formed during DNA replication where new strands are synthesized?

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

    Short segments of DNA synthesized on the lagging strand during replication are called ______ fragments.

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

    Match the following terms with their correct definitions:

    <p>Helicase = An enzyme that adds nucleotides to the new DNA strand Primase = An enzyme that unwinds the DNA double helix DNA polymerase = An enzyme that synthesizes short RNA primers DNA ligase = An enzyme that joins Okazaki fragments together</p> Signup and view all the answers

    Which of the following is NOT a component of the replisome?

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

    Telomeres are repetitive DNA sequences found at the ends of chromosomes that prevent DNA from deteriorating during replication.

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

    What is the name of the enzyme that maintains telomere length in certain cells?

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

    The process of DNA replication where each new DNA molecule has one original strand and one new strand is called ______ replication.

    <p>Semi-conservative</p> Signup and view all the answers

    Which of the following is a characteristic of eukaryotes?

    <p>Have complex cells with a nucleus (D)</p> Signup and view all the answers

    Flashcards

    Nucleotide

    The basic unit of DNA, consisting of sugar, phosphate, and a nitrogenous base.

    DNA Directionality

    DNA has 5’ and 3’ ends, indicating the direction new nucleotides are added.

    DNA Polymerase

    An enzyme that synthesizes new DNA by adding nucleotides to a growing strand in the 5' to 3' direction.

    Primase

    An enzyme that synthesizes short RNA primers, allowing DNA polymerase to add nucleotides.

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    Leading Strand

    The DNA strand synthesized continuously towards the replication fork.

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    Lagging Strand

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

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    Okazaki Fragments

    Short segments of newly synthesized DNA on the lagging strand.

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    DNA Ligase

    An enzyme that joins Okazaki fragments into a continuous DNA strand.

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    Telomeres

    Repetitive DNA sequences at chromosome ends that protect them from degradation during cell division.

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    Telomerase

    An enzyme that lengthens telomeres in stem and germ cells by adding TTAGGG repeats.

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    Semi-Conservative Model

    The correct DNA replication model where each new DNA molecule contains one original strand and one new strand.

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    Replisome

    A protein complex that coordinates DNA replication, including helicase and DNA polymerases.

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    Replication Fork

    The Y-shaped structure formed during DNA replication where the DNA strands are unwound.

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    Proofreading

    The ability of DNA polymerase to check and correct errors during DNA replication.

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    Nucleotide Base Pairing

    The pairing of adenine with thymine and cytosine with guanine in DNA strands.

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    Meselson-Stahl Experiment

    An experiment that confirmed the semi-conservative model by using different nitrogen isotopes.

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    Cell Cycle

    The life cycle of a cell, including growth, DNA replication, and division.

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    Interphase

    The phase of growth and preparation in the cell cycle, divided into G1, S, and G2 stages.

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    G1 Phase

    The first stage of Interphase where the cell grows and prepares for DNA replication.

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    S Phase

    The stage of Interphase where the cell duplicates its DNA.

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    G2 Phase

    The second growth stage in Interphase, ensuring DNA replication was successful.

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    M Phase

    The phase of the cell cycle where the cell divides into two identical daughter cells.

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    Mitosis

    The process during M Phase where duplicated DNA is separated into two identical sets.

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    Cytokinesis

    The final step of the cell cycle where the cytoplasm divides, forming two separate cells.

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    DNA Replication

    The process by which a cell duplicates its DNA before division, ensuring genetic consistency.

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    Semi-conservative Replication

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

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    Study Notes

    Cell Cycle

    • The cell cycle describes a cell's life, growth, DNA replication, and division.
    • Essential for growth, repair, and reproduction in multicellular organisms.
    • Two main phases: Interphase and M phase (mitotic phase).

    Interphase

    • A phase of growth and preparation for division, subdivided into three stages:
      • G1 Phase (Gap 1): Cell growth, protein synthesis, energy production; checks readiness for DNA replication.
      • S Phase (Synthesis): DNA replication – duplicates each chromosome.
      • G2 Phase (Gap 2): Further growth, protein synthesis; checks DNA replication accuracy.
    • G0 Phase: A resting phase where some cells remain until signals trigger re-entry into the cell cycle.

    M Phase (Mitotic Phase)

    • Involves cell division, splitting one cell into two identical daughter cells.
      • Mitosis: Separates duplicated DNA into two identical sets. Divided into four substages:
        • Prophase: Chromosomes condense, spindle fibers form.
        • Prometaphase: Nuclear envelope breaks down, spindle fibers attach to chromosomes.
        • Metaphase: Chromosomes align in the center of the cell.
        • Anaphase: Sister chromatids separate to opposite poles.
        • Telophase: Chromatids arrive at poles, new nuclear membranes form.
      • Cytokinesis: Cytoplasm divides, forming two identical daughter cells.

    DNA Replication

    • The process of duplicating DNA before cell division, ensuring each new cell gets a complete set.
    • Semi-conservative: Each new DNA molecule has one original and one new strand.

    DNA Structure

    • DNA is a double helix, like a twisted ladder.
    • Nucleotides are the building blocks.
    • Nucleotide Structure: Sugar (deoxyribose), phosphate group, nitrogenous base (A, T, C, G).
    • Base Pairing: A with T, C with G.
    • 5’ and 3’ ends: DNA strands have directionality; replication occurs 5' to 3'.

    DNA Polymerase

    • Enzymes that synthesize new DNA strands by adding nucleotides to an existing strand.
    • 5' to 3' direction.
    • Proofreading ability reduces errors.
    • DNA Polymerase III (prokaryotes): Main enzyme for DNA synthesis; highly processive, meaning it can catalyze thousands of base pairings at a time.

    Primase

    • An enzyme that synthesizes RNA primers needed for DNA polymerase to initiate DNA synthesis.

    DNA Replication Steps

    • Initiation: DNA unwinding at origins of replication (one in prokaryotes, multiple in eukaryotes).
    • Unwinding: Helicase unwinds the DNA. SSBPs stabilize the strands. Topoisomerase prevents supercoiling.
    • Primer Binding and Synthesis: Primase adds short RNA primers.
    • Elongation: DNA polymerase extends new strands from primers, synthesizing continuously (leading strand) and discontinuously (lagging strand) using Okazaki fragments.
    • DNA Ligase joins Okazaki fragments on the lagging strand.

    DNA Proofreading and Repair

    • Proofreading by DNA polymerase corrects errors during replication.
    • Repair mechanisms: Mismatch repair, Base excision repair (BER), Nucleotide excision repair (NER), and Double-strand break repair.

    Telomeres and Cellular Aging

    • Telomeres: Repetitive DNA sequences at chromosome ends, protecting from degradation during cell division.
    • Telomerase: Enzyme lengthening telomeres in some cells, leading to continued cell division but not in most somatic cells (leading to senescence).

    DNA Replication Models

    • Semi-conservative model: Correct model; each DNA molecule has one new and one old strand.
    • Meselson-Stahl experiment: Confirmed semi-conservative model using isotopes.
    • Conservative and dispersive models were disproven.

    Replisome

    • Complex of proteins (helicase, primase, DNA polymerases, sliding clamp) coordinating DNA replication.

    Key DNA Terminology

    • Terms like chromosome, chromatid, centromere, sister chromatids, mitotic spindle, base pairing, hydrogen bonds, replication origin, template strand, antiparallel structure, leading strand, lagging strand, primers, proofreading, mutations, exonuclease activity, Okazaki fragments, DNA ligase, semi-conservative replication, replication bubble, telomeres, senescence, eukaryotes, prokaryotes, replication fork, telomerase.

    Histones

    • Positively charged proteins that bind to negatively charged DNA, allowing tight coiling.
    • Five main types (H1, H2A, H2B, H3, H4) with specific roles in DNA organization.

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    Description

    Explore the stages of the cell cycle, including interphase and the mitotic phase. This quiz covers the critical processes of cell growth, DNA replication, and division essential for multicellular organisms. Test your understanding of the various phases and their significance in cellular function.

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