Genomes and Replication: E. coli vs Human
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Questions and Answers

What is the role of DnaA proteins in the DNA replication process?

  • They bind to the origin of replication and assist in breaking base pairs. (correct)
  • They act as terminators to halt the replication process.
  • They synthesize the RNA primers required for replication.
  • They serve as helicases to unwind the DNA.

    • Which feature of the origin of replication makes it easier for base pairs to separate?

  • The presence of A-T rich sequences. (correct)
  • The location of replication terminators.
  • The binding of helicase proteins alone.
  • The presence of C-G rich sequences.

    • What is the primary function of DnaB proteins during DNA replication?

  • To unwind the DNA double helix at the replication fork. (correct)
  • To determine the size of the genome during the process.
  • To create RNA primers that initiate replication.
  • To bind and hold the DNA strands apart.

    • What is the role of primase in the replication process?

    <p>It synthesizes RNA primers that initiate replication.</p> Signup and view all the answers

    How do tus proteins function in DNA replication?

    <p>They act as terminators that signal the end of replication.</p> Signup and view all the answers

    What is the approximate size of the human genome?

    <p>6400 Mb</p> Signup and view all the answers

    How many linear DNA molecules comprise the human genome?

    <p>24</p> Signup and view all the answers

    What is the role of Tus proteins in bacteria?

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

    What is a characteristic of E. coli genome replication?

    <p>Two replication forks are formed bidirectionally</p> Signup and view all the answers

    Which of the following statements is true about human DNA replication?

    <p>Each replication fork copies about 150 kb of DNA</p> Signup and view all the answers

    What is the total number of chromosomes in a normal human diploid cell?

    <p>46</p> Signup and view all the answers

    What is the role of origins of replication in the genome?

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

    How is the E. coli genome structured?

    <p>It is circular and consists of a single DNA molecule</p> Signup and view all the answers

    What is the primary function of the Tus protein in E. coli?

    <p>To bind to terminator sequences in the genome</p> Signup and view all the answers

    What characterizes the permissive and non-permissive faces of Tus proteins?

    <p>They allow the replication fork to pass in one direction but not the other</p> Signup and view all the answers

    How many kilobases of DNA does each replication fork typically copy in human DNA replication?

    <p>150 kb</p> Signup and view all the answers

    What happens during the interaction of the Ter C6 base with the Tus lock domain?

    <p>It causes replication fork arrest</p> Signup and view all the answers

    Where do replication origins arise in human DNA?

    <p>At multiple sites on each chromosomal DNA molecule</p> Signup and view all the answers

    What is a consequence of the Tus protein's effect on the replication fork?

    <p>Replication forks become trapped at specific locations</p> Signup and view all the answers

    In what manner do replication forks behave during DNA replication in humans compared to E. coli?

    <p>They merge without needing exact control like circular DNA</p> Signup and view all the answers

    What happens if a replication fork in E. coli reaches a non-permissive face of a Tus protein?

    <p>The replication fork becomes trapped</p> Signup and view all the answers

    What is the main function of higher order packaging of DNA in cells?

    <p>To accommodate the large amounts of DNA within a cell</p> Signup and view all the answers

    Which of the following accurately describes euchromatin?

    <p>It is loosely packed and more accessible for transcription</p> Signup and view all the answers

    What role do centromeres play in cell division?

    <p>They facilitate the attachment of spindle fibers during mitosis</p> Signup and view all the answers

    What is a primary function of telomeres in chromosomes?

    <p>To ensure complete DNA replication of chromosome ends</p> Signup and view all the answers

    Which of these is NOT a unique feature of chromosomes necessary for their maintenance and segregation?

    <p>The configuration of euchromatin</p> Signup and view all the answers

    What is the primary function of nucleosomes in cells?

    <p>To compact DNA into higher order structures</p> Signup and view all the answers

    Euchromatin is primarily characterized by which of the following?

    <p>Active genes in a less compact state</p> Signup and view all the answers

    Which of the following statements about heterochromatin is true?

    <p>It consists of densely packed DNA.</p> Signup and view all the answers

    What is the role of centromeres in chromosomes?

    <p>To hold sister chromatids together</p> Signup and view all the answers

    What is a key function of telomeres?

    <p>They protect chromosome ends from degradation.</p> Signup and view all the answers

    How does the composition of constitutive heterochromatin differ from facultative heterochromatin?

    <p>Facultative heterochromatin varies between cell types.</p> Signup and view all the answers

    Which component is added to form a chromatosome?

    <p>A linker histone (H1)</p> Signup and view all the answers

    What is the higher-order chromatin structure of 30 nm fibers characterized by?

    <p>Stacked nucleosomes in a zig-zag arrangement</p> Signup and view all the answers

    What initiates the higher order packaging of DNA into structures like metaphase chromosomes?

    <p>Chemical modification of histones</p> Signup and view all the answers

    Why is it important for nucleosomes to detach during replication of DNA?

    <p>To allow access to DNA for copying</p> Signup and view all the answers

    The banding pattern observed in stained metaphase chromosomes is useful for what purpose?

    <p>Mapping positions of genes</p> Signup and view all the answers

    Which histone variant is specifically present at centromeres?

    <p>CENP-A</p> Signup and view all the answers

    What happens to the length of a DNA molecule when packaged into nucleosomes?

    <p>It reduces to one-sixth of its original length</p> Signup and view all the answers

    Study Notes

    Genomes I

    • E. coli genome: 4.64 Mb, single, circular DNA molecule
    • Human genome: 3200 Mb, split into 24 linear DNA molecules
      • Shortest: 48 Mb
      • Longest: 250 Mb
      • Normal diploid cell: 46 chromosomes (1-22 and either XX or XY), 6400 Mb total DNA
    • Genome: complete set of DNA molecules in an organism

    Replication Origins

    • E. coli replication: starts at a single origin, bidirectional replication forks
    • Human replication: multiple origins on each chromosome, bidirectional replication forks
    • Replication origin (E. coli): fixed position on the chromosome, DnaA proteins bind here to initiate replication
    • Replication origin (Human): multiple, dynamic locations along chromosomes, not always at the same sites
      • Each replication fork copies about 150 kb of DNA

    Replication Termination

    • Circular DNA (like in E. coli) must have a mechanism to stop replication forks from colliding, because these are bidirectional
    • E. coli replication: Replication forks meet at specific terminator sequences that act as binding sites for Tus proteins
    • Tus proteins: regulate the direction of replication forks, allowing the forks to only travel in one direction but not the other; this prevents the replication fork from colliding with its other fork during duplication
    • Human replication: forks merge; no need for specific terminator sequences for control like in a circular genome

    Replication Fork Initiation

    • DnaA proteins: bind to the origin of replication region
      • Winding of DNA around DnaA proteins: causes stress on the DNA, which forces base pairs to break, allowing replication to begin at the origin of replication. This origin is rich in A-T base pairs (easier to pull apart than G-C base pairs).
    • DnaB helicase: unwinds the DNA using energy from ATP
    • Primosome: made by two primase enzymes, synthesizes RNA primers that start the leading strand replication.
    • Single-strand binding proteins (SSBs): protect single-stranded DNA at the replication fork.
    • DNA topoisomerase: relieves tension in the DNA molecule to prevent supercoiling
    • DNA polymerase III: synthesizes DNA on the leading and lagging strand
    • DNA polymerase I and DNA ligase: removes RNA primers and joins together Okazaki fragments on the lagging strand
    • Gamma complex (clamp loader): loads DNA polymerase onto the template strand and moves along this strand
    • Beta complex (sliding clamp): allows DNA polymerase to stay attached to the DNA molecule.
    • In human cells: DNA pol alpha synthesizes RNA primers, DNA pol delta synthesizes DNA, FEN1 removes RNA primers, DNA ligase joins Okazaki fragments, PCNA (proliferating cell nuclear antigen) binds DNA polymerase delta

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    Description

    Explore the differences between the genomes of E. coli and humans in this quiz. Learn about replication origins, mechanisms, and chromosome structures, including the unique features of each organism's DNA. Test your knowledge on genome sizes, structures, and replication processes.

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