1. Cell Division Controls in Mammalian Cells
Lecture 38 BSCI 420, 412 Dec 2, 2002
“ One must show great respect to anything that divides
exponentially, no matter how small.” -Garrett Harding
Studies on mammalian cells in culture
The mammalian cell cycle control system

2. The results of fusion of mammalian cells at different phases
of the cell cycle:
G1,S,G2 M
M-phase nucleus
Stays in M, other
Nucleus enters
Mitosis
S contain a pos signal. G2 block to re-replication. M pos signal

3. Mammalian cell cycle control is more complicated than in yeasts.
At least 4 different cyclin/CdK combinations active in diff phases:
G1 (Cycling G1/S
cell) kinase (Start) S-kinase M-kinase
Cdk Cycl D Kinase
Activity CdK4
Cycl E Cycl A Cycl B
CdK2 CdK 1or CdK 1 __________________________________________________
G1 S G2 M

4. The role of myc
In cell
proliferation

6. Initiation of DNA replication
Mcm proteins
form helicase
Each replicon
repl only once.
Phosphorylated
ORCs & Mcms
Cause block to rereplication p-Mcms are exported
from nucleus

8. Activation of M-phase CdKinase (MPF)