KINE 1000 Lecture Notes - Lecture 16: Spindle Apparatus, Origin Recognition Complex, Helicase
4 Jun 2018
School
Department
Course
Professor
S-Cdk Initiates DNA Replication Once Per
Cycle
• DNA replication begins at origin of replication
• DNA replication initiated at origins when DNA helicase unwinds double helix &
DNA replication enzymes are loaded onto two single-stranded templates
• Elongation phase of replication is when replication machinery moves outward
from origin
• Chromosome duplication occurs once per cycle
• Initiation phase of DNA replication is divided into two distinct steps:
1. Late mitosis/Early G1- DNA helicase is loaded onto origin to create
prereplicative complex (preRC). DNA synthesis is only permitted at origins
containing preRC
2. During S-phase, DNA helicases are activated resulting in DNA unwinding &
initiation of DNA synthesis
• Origin cannot be reused until new preRC is assembled at end of mitosis
• Origin recognition complex (ORC) binds to replication origin
o In late mitosis/early G1 proteins cdc6 & cdt1 collaborate w/ORC to load
inactive helicase to origin to give preRC
o In S-phase, s-cdk triggers origin activation by phosphorylating initiator
proteins which activate DNA helicase & recruits DNA synthesis machinery.
Protein kinase DDK is activated in s-phase & helps drive origin activation by
phosphorylating subunit of DNA helicase
• As s-cdk initiates DNA replication, it prevents assembly of new pre-RCs
o S-cdk phosphorylates & inhibits ORC & cdc6 proteins
• Inactivation of APC/C in late G1 helps turn off preRC assembly
o In late mitosis/early G1, APC/C triggers destruction of cdt1 inhibitor- geminin.
This allows activation of cdt1 → allows formation of pre-RC
o In late G1, APC/C is turned off, geminin accumulates & inhibits cdt1 →
prevents pre-RC formation in S-phase to mitosis.
o Ensures each origin is fired once per cycle→ formation of pre-RC in early G1
o At end of mitosis, APC/C activation leads to inactivation of cdks, destruction
of cdt inhibitor (geminin). ORC & cdc7 are dephosphorylated & cdt1 is
activated allowing preRC to assembly
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Cycle: dna replication begins at origin of replication, dna replication initiated at origins when dna helicase unwinds double helix & Dna replication enzymes are loaded onto two single-stranded templates: elongation phase of replication is when replication machinery moves outward from origin, chromosome duplication occurs once per cycle. Initiation phase of dna replication is divided into two distinct steps: late mitosis/early g1- dna helicase is loaded onto origin to create prereplicative complex (prerc). Protein kinase ddk is activated in s-phase & helps drive origin activation by phosphorylating subunit of dna helicase: as s-cdk initiates dna replication, it prevents assembly of new pre-rcs, s-cdk phosphorylates & inhibits orc & cdc6 proteins. Inactivation of apc/c in late g1 helps turn off prerc assembly: in late mitosis/early g1, apc/c triggers destruction of cdt1 inhibitor- geminin. Orc & cdc7 are dephosphorylated & cdt1 is activated allowing prerc to assembly.
