Arthur Kornberg's Discovery of DNA Polymerase I
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Questions and Answers

What did Arthur Kornberg demonstrate in 1957?

  • The existence of DNA ligase
  • The existence of DNA polymerase II
  • The existence of DNA helicase
  • The existence of DNA polymerase I (correct)

    • What is the function of DNA polymerase I in DNA replication?

  • To synthesize DNA in a 3' to 5' direction
  • To break hydrogen bonds between DNA strands
  • To synthesize DNA in a 5' to 3' direction (correct)
  • To join Okazaki fragments on the lagging strand

    • What is the role of primase in DNA replication?

  • To make a short RNA primer that matches the single-stranded DNA (correct)
  • To break hydrogen bonds between DNA strands
  • To join Okazaki fragments on the lagging strand
  • To synthesize DNA in a 5' to 3' direction

    • During DNA replication, what happens to the RNA primer?

    <p>It is removed by DNA polymerase's exonuclease function</p> Signup and view all the answers

    What is the direction of DNA synthesis on the leading strand?

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

    What is the role of DNA helicase during DNA replication?

    <p>To break hydrogen bonds between DNA strands</p> Signup and view all the answers

    What is the function of DNA ligase during DNA replication?

    <p>To join Okazaki fragments on the lagging strand</p> Signup and view all the answers

    What is the phase of the cell cycle during which DNA replication occurs?

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

    Where does the metabolism of carbohydrates, amino acids, and nucleotides occur?

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

    What is the function of the Rough Endoplasmic Reticulum?

    <p>Membrane associated protein synthesis and secretion</p> Signup and view all the answers

    What is the term for a protein as it is being formed by a ribosome before it folds into its active shape?

    <p>Nascent protein</p> Signup and view all the answers

    What is the site of lipid synthesis in a cell?

    <p>Smooth Endoplasmic Reticulum</p> Signup and view all the answers

    What is the function of the Golgi Apparatus in protein synthesis?

    <p>Modification and packaging of proteins and lipids</p> Signup and view all the answers

    What is the characteristic feature of the Rough Endoplasmic Reticulum?

    <p>Presence of embedded ribosomes</p> Signup and view all the answers

    Where do proteins move from in the Golgi Apparatus?

    <p>Convex/cis end to concave/trans end</p> Signup and view all the answers

    What is the shape of the cisternae in the Golgi Apparatus?

    <p>Stacked and curved</p> Signup and view all the answers

    What is the primary function of the nucleus in a eukaryotic cell?

    <p>To store and coordinate the cell's activities</p> Signup and view all the answers

    Which of the following is a characteristic of heterochromatin?

    <p>It is condensed and has no active RNA synthesis</p> Signup and view all the answers

    What is the function of the nuclear envelope?

    <p>To allow macromolecules to pass through the nucleus</p> Signup and view all the answers

    What is the site of ribosomal RNA synthesis in a eukaryotic cell?

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

    What is the central dogma of molecular biology?

    <p>Genetic information flows from DNA to RNA to protein</p> Signup and view all the answers

    What is a characteristic of prokaryotic cells?

    <p>They have a circular plasmid genome</p> Signup and view all the answers

    What is the function of euchromatin?

    <p>It is involved in gene expression</p> Signup and view all the answers

    What is the term for a compartment of a cell with a specific function?

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

    What is the primary function of DNA ligase during DNA replication?

    <p>To create phosphodiester bonds between sugar and phosphate groups</p> Signup and view all the answers

    What is the main difference between exonuclease and endonuclease?

    <p>Exonuclease removes nucleotides from the ends, while endonuclease removes nucleotides within the polynucleotide molecule</p> Signup and view all the answers

    What is the purpose of the exonuclease domain in DNA polymerase?

    <p>To proofread and remove incorrectly matched bases</p> Signup and view all the answers

    Why is DNA polymerase I not the main replication enzyme in E. coli?

    <p>It is too slow to replicate the genome</p> Signup and view all the answers

    What is the definition of processivity in DNA polymerase?

    <p>The number of nucleotides added to a growing DNA chain before the enzyme dissociates</p> Signup and view all the answers

    What happens when DNA polymerase I stalls due to an incorrect nucleotide being added?

    <p>The enzyme stalls and cannot add the next nucleotide to the chain</p> Signup and view all the answers

    What is the result of the semi-conservative replication model?

    <p>Two DNA molecules, each with one original DNA strand and one new DNA strand</p> Signup and view all the answers

    Why are there more DNA polymerases in E. coli?

    <p>To increase the speed of DNA replication</p> Signup and view all the answers

    What is the fundamental principle of the conservative model of DNA replication?

    <p>The original DNA molecule remains intact, and an entirely new DNA molecule is synthesized.</p> Signup and view all the answers

    What is the purpose of density gradient centrifugation in the Meselson-Stahl experiment?

    <p>To separate DNA molecules based on density.</p> Signup and view all the answers

    What is the significance of the intermediate band observed in the Meselson-Stahl experiment?

    <p>It supports the semiconservative model of DNA replication.</p> Signup and view all the answers

    In the Meselson-Stahl experiment, what is the purpose of growing E. coli bacteria in a medium containing a heavy isotope of nitrogen?

    <p>To make the DNA molecules denser.</p> Signup and view all the answers

    What is the outcome of the Meselson-Stahl experiment that supports the semiconservative model of DNA replication?

    <p>The formation of DNA molecules with a mix of N-15 and N-14 isotopes.</p> Signup and view all the answers

    What is the main difference between the conservative and dispersive models of DNA replication?

    <p>The conservative model involves the synthesis of new DNA molecules, whereas the dispersive model involves the fragmentation of the original DNA molecules.</p> Signup and view all the answers

    What is the significance of transferring the labeled E. coli bacteria to a medium containing a lighter isotope of nitrogen in the Meselson-Stahl experiment?

    <p>To allow the bacteria to replicate their DNA in the new medium.</p> Signup and view all the answers

    What is the result of DNA replication according to the semiconservative model?

    <p>The synthesis of new strands complementary to the old ones.</p> Signup and view all the answers

    Study Notes

    Arthur Kornberg's Discovery

    • In 1957, Arthur Kornberg demonstrated the existence of DNA polymerase I, which has three enzymatic activities in a single polypeptide: a 5' to 3' DNA polymerizing activity, a 3' to 5' exonuclease activity, and a 5' to 3' exonuclease activity.

    Semi-Conservative DNA Replication

    • DNA replication occurs in the synthesis phase (S phase) of the cell cycle.
    • The process involves three stages: initiation, elongation, and termination.
    • Initiation: DNA helicase untwists the DNA strands, breaking their hydrogen bonds, and primase makes a short RNA primer that matches the single-stranded DNA.
    • Elongation: DNA polymerase builds a new 5' to 3' strand on the 3' to 5' strand (leading strand), and on the 5' to 3' strand (lagging strand), new DNA polymerases start due to helicase action, creating Okazaki fragments.
    • Termination: DNA ligase connects the remaining Okazaki fragments and the sections where forks have met, creating phosphodiester bonds between sugar and phosphate groups.

    Cellular Components

    • Cytosol: involved in metabolism, protein synthesis (free ribosomes).
    • Endoplasmic Reticulum (ER):
      • Rough ER: translation of mRNA into membrane-associated proteins or for secretion out of the cell, with ribosomes attached to the outer surface of the membranes.
      • Smooth ER: synthesis of lipids, Ca2+ storage, and steroid production, with no embedded ribosomes.
    • Golgi Apparatus: modifies and packages proteins and lipids for delivery to other organelles or for secretion out of the cell.

    DNA Replication Models

    • Conservative Model: the original DNA molecule remains intact, and an entirely new DNA molecule is synthesized.
    • Dispersive Model: the original parental DNA molecule breaks into fragments, which serve as templates for the synthesis of new DNA.
    • Semi-Conservative Model: each newly formed DNA molecule consists of one parental strand and one daughter strand, supported by the Meselson-Stahl Experiment.

    Meselson-Stahl Experiment

    • E. coli bacteria were grown in a medium containing a heavy isotope of nitrogen (N-15), making their DNA denser.
    • The labeled bacteria were transferred to a medium containing a lighter isotope of nitrogen (N-14), and allowed to replicate their DNA.
    • DNA samples were collected at various time intervals and subjected to density gradient centrifugation, separating DNA molecules based on density.
    • An intermediate band containing a mix of N-15 and N-14 DNA was observed, supporting the semi-conservative model.

    Cell Structure

    • Prokaryote Cell: no nucleus, membrane-bound organelles, genome is found as a circular plasmid DNA, and plasmid is important for gene modification.
    • Eukaryotic Cell Structure: organelle is a compartment of a cell with a specific function.
    • Nucleus: contains DNA, nucleoproteins, and RNA, and functions as the control center for the cell's activities, such as growth, metabolism, protein synthesis, and cell division.
    • Nucleolus: site of ribosomal RNA (rRNA) synthesis, found within the nucleus.
    • Nuclear Envelope: a double-layered membrane with nuclear pores, allowing macromolecules to pass through when entering or exiting the nucleus.

    DNA Polymerase and Exonuclease

    • Endonucleases: enzymes that remove successive nucleotides within the polynucleotide molecules.
    • Exonucleases: enzymes that remove successive nucleotides from the ends of a polynucleotide molecules.
    • The exonuclease activity in DNA polymerase I serves a proofreading function, removing incorrectly matched bases.
    • DNA polymerase I is not the main replication enzyme due to its slow speed and moderate processivity.

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    Description

    Learn about Arthur Kornberg's groundbreaking discovery in 1957, where he demonstrated the existence of DNA polymerase I, an enzyme with three enzymatic activities. Discover its roles in DNA polymerization and exonuclease.

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