Eukaryotic cells must copy large, linear chromosomes while DNA is packaged around histone proteins. This lesson explains how replication begins at many places along each chromosome and how specialized enzymes coordinate DNA synthesis.
Eukaryotic genomes are much larger and more complex than prokaryotic genomes. A human haploid set contains about 3 billion base pairs, and about 6 billion base pairs are copied during the S phase of the cell cycle. Because eukaryotic chromosomes are long and linear, replication starts at many origins of replication on each chromosome rather than at a single origin. Humans may have as many as 100,000 origins across the genome.
All flashcards
Why does eukaryotic chromatin need remodeling during replication?
DNA is wrapped around histones in nucleosomes. Temporarily altering or displacing histones makes the DNA accessible to replication enzymes; histones are then replaced.
What do helicase and topoisomerase do at a replication fork?
Helicase uses ATP to unwind the DNA double helix. Topoisomerase relieves the supercoiling that builds up ahead of the moving fork.
Which polymerases synthesize the leading and lagging strands?
Pol ε primarily synthesizes the leading strand continuously, while pol δ synthesizes the lagging strand as Okazaki fragments. Pol α first adds a short DNA segment after the RNA primer.
How are Okazaki fragments joined?
RNA primers are processed and replaced with DNA, and DNA ligase seals the remaining nicks by forming phosphodiester bonds.
How does telomerase help maintain chromosome ends?
Telomerase uses its built-in RNA template to add DNA to the 3′ end of a chromosome, providing additional template for complementary-strand synthesis.
Quiz questions
Why do eukaryotic chromosomes use many origins of replication?Answer: They allow separate chromosome regions to be copied in parallel.
What is the role of histone displacement during eukaryotic DNA replication?Answer: It makes DNA accessible to replication proteins before histones are replaced.
Which enzyme relieves supercoiling ahead of a replication fork?Answer: Topoisomerase
Which polymerase primarily synthesizes the leading strand during nuclear chromosome replication?Answer: Pol ε
How does telomerase extend a eukaryotic chromosome end?Answer: It uses its RNA template to add DNA to the strand's 3′ end.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.