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Replication in Eukaryotes01:29

Replication in Eukaryotes

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In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fulfill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.
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Replication in Prokaryotes01:32

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DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to the single origin of replication (ori) on the cell's circular chromosome. Replication then proceeds around the entire circle of the chromosome in each direction from the two replication forks, resulting in two DNA molecules.
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DNA replication involves the separation of the two strands of the double helix, with each strand serving as a template from which the new complementary strand is copied.  After replication, each double-stranded DNA includes one parental or “old” strand and one “new” strand. This is known as semiconservative replication. The resulting DNA molecules have the same sequence and are divided equally into the two daughter cells.
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The DNA Replication Fork01:02

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An organism’s genome needs to be duplicated in an efficient and error-free manner for its growth and survival. The replication fork is a Y-shaped active region where two strands of DNA are separated and replicated continuously. The coupling of DNA unzipping and complementary strand synthesis is a characteristic feature of a replication fork.   Organisms with small circular DNA, such as E. coli, often have a single origin of replication; therefore, they have only two replication...
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DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the minichromosome maintenance (MCM) helicase and other factors such as Cdc45 and the associated GINS complex.The unwound single strands are protected by replication protein A (RPA) until DNA polymerase starts synthesizing DNA at the 5’ end of the strand in the same direction as the replication fork. To prevent the replication fork from falling apart,...
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The cell cycle is a series of events leading to DNA duplication followed by the division of cell content to form two daughter cells. The cell cycle progresses in four stages—the cell increases in size (gap 1 or G1-phase), duplicates its DNA (synthesis or S-phase), prepares to divide (gap 2 or G2-phase), and divides (mitosis or M-phase).
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DNA replication in primary hepatocytes without the six-subunit ORC.

Róża K Przanowska1, Yuechuan Chen2, Takayuki-Okano Uchida3

  • 1Dept. of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, United States.

Elife
|April 30, 2025
PubMed
Summary
This summary is machine-generated.

Primary cells can initiate DNA replication without the ORC2 protein, challenging previous understandings of DNA replication initiation. This finding suggests alternative pathways for replication in certain cell types.

Keywords:
cell biologygeneticsgenomicsmousemouse embryo fibroblastsmouse liverprimary hepatocytes

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • The Origin Recognition Complex (ORC) is crucial for initiating DNA replication in eukaryotes.
  • Cancer cells can tolerate the loss of individual ORC subunits (ORC1, ORC2, ORC5).
  • ORC1 is dispensable in mouse liver endo-reduplication, potentially due to CDC6 homolog substitution.

Purpose of the Study:

  • To investigate the necessity of ORC2 for DNA replication in primary cells.
  • To determine if primary cells can initiate DNA replication without ORC2, similar to cancer cells.

Main Methods:

  • Conditional deletion of ORC2 in mice.
  • Analysis of DNA synthesis and proliferation in mouse embryo fibroblasts and hepatocytes.
  • Assessment of ORC1 and ORC2 deletion effects on liver endo-reduplication.

Main Results:

  • Mouse hepatocytes can proliferate and endo-replicate in vitro and in vivo without ORC2.
  • Simultaneous deletion of ORC1 and ORC2 in mouse livers still permits endo-reduplication.
  • Endo-reduplication initiates DNA synthesis, indicating replication can occur without ORC.

Conclusions:

  • Primary cells, like cancer cell lines, can initiate DNA replication without ORC.
  • MCM2-7 loading and replication initiation are possible through ORC-independent pathways in certain contexts.
  • These findings redefine the essentiality of ORC for DNA replication initiation in eukaryotes.