SA node has an unstable resting membrane potential.

The “resting membrane potential” of the sinus nodal fiber between discharges has a negativity of about −55 to −60 millivolts.

TLS Online TPP Program

#Id: 8935

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 8936

#Unit 2. Cellular Organization

When a kinetochore is unattached, the outer kinetochore component Knl1 is phosphorylated by the checkpoint kinase Mps1.

TLS Online TPP Program

#Id: 8937

#Unit 2. Cellular Organization

Phosphorylated Knl1 binds the checkpoint protein kinase Bub1-Bub3 and checkpoint protein BubR1. These three proteins, recruit the Mad1-Mad2 complex to the kinetochore.

TLS Online TPP Program

#Id: 8938

#Unit 2. Cellular Organization

The Mad1-Mad2 complex bound to a kinetochore adopts the active closed form (Mad2-C) and has the ability to convert inactive open Mad2 (Mad2-O) in the cytoplasm into active closed Mad2 is able to inhibit APC/Ccdc²⁰

TLS Online TPP Program

#Id: 8939

#Unit 2. Cellular Organization

checkpoint factors Bub1-Bub3, BubR1 and Mad2-C Together, these proteins form the mitotic checkpoint complex

TLS Online TPP Program

#Id: 8940

#Unit 2. Cellular Organization

Knl1 eliminating checkpoint protein binding sites at kinetochores. p31comet disassembles the MCC, allowing APC/Ccdc20 to degrade mitotic cyclins and securin to trigger anaphase.