The individual fibers are separated by membranes, but depolarization spreads radially (syncytium) because of the presence of gap junctions.

TLS Online TPP Program

#Id: 8618

#Unit 2. Cellular Organization

Cdc25 phosphatase Activates CDKs in fission yeast

TLS Online TPP Program

#Id: 8619

#Unit 2. Cellular Organization

INK4s

bind to CDK4 and CDK6 monomers, blocking their interaction with cyclin D

TLS Online TPP Program

#Id: 8620

#Unit 2. Cellular Organization

A second class of CKIs found in metazoan cells is the Cip/Kip family of CKIs, consists of three proteins—p21CIP, p27KIP1, and p57KIP2. 

TLS Online TPP Program

#Id: 8621

#Unit 2. Cellular Organization

The Cip/Kip family members bind to cyclin-bound CDKs and block the activity of cyclin D-, E-, A-, and B-containing complexes.

TLS Online TPP Program

#Id: 8622

#Unit 2. Cellular Organization

Cyclins are degraded through the action of two different E3-ligases:

1. SCF (Skp1, Cullin, and F-box proteins) 

2. APC/C or cyclosome

TLS Online TPP Program

#Id: 8623

#Unit 2. Cellular Organization

SCF and APC/C are multisubunit ubiquitin-protein ligases that belong to the RING finger family of ubiquitin-protein ligases.