DNA Replication in Eukaryotes | Termination

Summary

This video explains the termination of DNA replication in eukaryotes, highlighting the differences from prokaryotic replication. It covers the role of the MCM helicase complex in DNA unwinding, the synthesis of leading and lagging strands, and the critical step where the replication forks converge. The SCF ubiquitin ligase complex marks the MCM helicase for removal, and the P97 segregase disassembles it, signaling the end of replication. This process ensures proper termination of DNA replication in eukaryotic cells, completing the replication cycle.

Takeaways

• 😀 Termination of DNA replication in eukaryotes is different from prokaryotes due to the linear nature of eukaryotic DNA.
• 😀 In eukaryotes, DNA replication involves multiple origins of replication, each with its own helicase (MCM complex) to unwind the DNA.
• 😀 Replication in eukaryotes is terminated when two replication forks meet, initiating a process of replication termination.
• 😀 The MCM complex (helicase) is central to DNA unwinding during replication and is involved in the termination process.
• 😀 The helicase MCM complexes approach each other from different origins of replication, completing the DNA replication process.
• 😀 During termination, a primer is added to the 3' end of the DNA strand, allowing polymerase to extend it and form the leading strand.
• 😀 On the lagging strand, multiple primers are used to create Okazaki fragments during the elongation phase of DNA replication.
• 😀 The SCF ubiquitin ligase complex plays a key role in terminating DNA replication by ubiquitinating the MCM helicase complex.
• 😀 The ubiquitinated MCM helicase complex is recognized by the p97 protein, which disassembles the complex and ends the replication process.
• 😀 Once the MCM helicase complex is removed from the DNA strand, the DNA replication process is complete in eukaryotes.

Q & A

How is the termination of DNA replication in eukaryotes different from prokaryotes?

In eukaryotes, DNA replication termination occurs when two replication forks meet at specific termination sites, whereas in prokaryotes, termination typically happens when the replication fork reaches a termination region of the circular DNA molecule.

What role does the MCM complex play in DNA replication termination in eukaryotes?

The MCM complex acts as the helicase during DNA replication in eukaryotes. It unwinds the DNA strands, and its disassembly at the end of replication is crucial for terminating the process.

What is the CMG complex, and why is it not shown in the diagram?

The CMG complex consists of the MCM helicase along with additional associated proteins. It is not shown in the diagram because the focus is primarily on the MCM complex for the termination process.

What is the significance of the 3' terminus end in DNA replication?

The 3' terminus end is critical for the extension of the DNA strand during replication. A primer is added to this end to allow polymerases to extend it, forming the leading strand.

What happens during lagging strand synthesis?

During lagging strand synthesis, multiple primers are added, and DNA polymerase synthesizes the strand in fragments called Okazaki fragments, which are later joined together.

What is the function of the SCF ubiquitin ligase complex in the termination of DNA replication?

The SCF ubiquitin ligase complex catalyzes the ubiquitination of the MCM helicase, marking it for disassembly and thereby halting DNA replication.

What does the P97 protein do during the termination of DNA replication?

The P97 protein recognizes the polyubiquitinated MCM complex and helps in its disassembly by segregating the helicase complex from the DNA, thus terminating the replication process.

How does the ubiquitination of MCM contribute to the termination of DNA replication?

Ubiquitination of the MCM complex signals that it should be disassembled. Although it is typically targeted for degradation, in this case, it is disassembled without degradation to stop the replication machinery.

What happens when two replication forks meet during eukaryotic DNA replication?

When two replication forks meet, the DNA replication process is terminated. The MCM complex is disassembled, and other associated proteins are removed, halting further DNA synthesis.

What is the role of ATP in the segregation of the MCM complex by P97?

ATP is required for the function of the P97 protein, which uses energy from ATP hydrolysis to segregate the MCM complex, facilitating its disassembly and the termination of DNA replication.