In cardiac muscle, the action potential is caused by opening of three types of channels

Voltage activated fast sodium channels 

L-type calcium channels (slow calcium channels or calcium-sodium channels)

Voltage activated potassium ion channels

TLS Online TPP Program

#Id: 6015

#Unit 3. Fundamental Processes

The origin enters S phase in the condition of a prereplication complex, which contains ORC, Cdc6, Cdt1, and the inactive helicase

TLS Online TPP Program

#Id: 6016

#Unit 3. Fundamental Processes

The MCM2-7 proteins form a six-member ring-shaped complex around DNA. MCM2,3,5 are regulatory, while MCM4,6,7 have the helicase activity.

TLS Online TPP Program

#Id: 6017

#Unit 3. Fundamental Processes

In mammalian cells, Cdt1 is targeted for degradation by the action of a protein complex that is recruited to the origin of replication by PCNA, the eukaryotic counterpart of the bacterial b clamp.

TLS Online TPP Program

#Id: 6018

#Unit 3. Fundamental Processes

As the transition from G1 to S phase begins, CDK/cyclins recruit cdc45 and the GINS complex to the MCM helicase, which then becomes known as the CMG complex (Cdc45-MCM-GINS)

TLS Online TPP Program

#Id: 6019

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6020

#Unit 3. Fundamental Processes

As cells enter into the S phase of the cell cycle, two kinases, CDK and DDK, are activated.  DDK phosphorylates loaded Mcm2-7 helicase, and CDK phosphorylates Sld2 and Sld3.Phosphorylated Sld2 and Sld3 bind to Dpb11, and together these proteins facilitate binding of the helicase-activating proteins, Cdc45 and GINS, to the helicase.