Eukaryotic DNA Replication Animation || Formation of Initiation complex
#biologyanimation #dnareplication #cellbiology 1. In earlier videos, we have discussed DNA replication in prokaryotes, now in this video, we will learn about the initiation of DNA replication in eukaryotes. 2. Origin of replication in yeast is known as Autonomously replicating sequences or ARS, which includes a consensus sequence, A-domain and additional elements. 3. As cells enter the G1 phase of the cell cycle, the Origin recognition complex or ORC bound to ATP comes and binds to the ARS region. 4. Now, this ORC recruits ATP-bound helicase loading protein CDC6. 5. Next, two copies of hexamer Mini-chromosome maintenance Protein complex or MCM 2-7 complex attach alongside another helicase loading protein, CDT1. 6. This makes the whole complex unstable and this triggers ATP hydrolysis by cdc6. 7. These results in the MCM complex encircling the double-stranded DNA and the release of cdc6 and cdt1 from the origin. 8. Here MCM complex functions as helicase. 9. During the G1 phase, only the unwinding of DNA occurs. 10. As the cell enters the S phase of the cell cycle initiation of replication starts. 11. This starts with the activation of two protein kinases, cyclin-dependent kinase or CDK and Dbf4-dependent kinase or DDK. 12. Once activated, DDK phosphorylates the mcm2-7 complex. 13. Whereas, CDK phosphorylates two other replication proteins sld2 and sld3. 14. Phosphorylated sld2 and sld3 then bind to Dpb11 and they all together attach to the origin complex. 15. This facilitates the binding of helicase-activating proteins, CDC 45 and GINS to the complex. 16. Now this, cdc45 and GINS form a stable complex with the MCM2-7 helicase which is called as CMG complex. 17. This complex dramatically activates MCM2-7 helicase activity. 18. Before unwinding DNA polymerase (€) is recruited to the helicase at both strands. 19. After the formation of this complex, sld2,sld3 and dpb1 are released and the unwinding of DNA strands starts. 20. As the DNA unwinds, DNA polymerase alpha along with primase and DNA Polymerase delta are recruited on both strands. 21. After that, the DNA elongation begins.
