Download Prokaryotes

Cyclin-dependent kinases (CDK) along with cyclins (D, E, A, B), are
the major control switches for the cycle
The diagram of the cell cycle control: arrows show the direction of cell cycle
progression, X– main checkpoint ; CDK (4, 2, cdc2)- kinases; D, E, A, B – the
different cyclins
Genetic regulation of cell cycle progression
MPF (Maturation Promoting Factor) includes the Cdk and cyclins that trigger the
progression
-p53 is a protein to block the cell cycle if the DNA is damaged. If the damage is severe,
this protein can cause apoptosis (cell death). P53 levels are increased in damaged
cells.
A p53 situation is the most frequent mutation leading to cancer. An extream case of this
Li Fraumeni syndrome, when a mutation in p53 gene leads to a high frequency of
cancer affects inindividuals.
-p27 is a protein that binds to cyclin and Cdk blocking entry in to S phase. Recent
reseach (Nature medicine 3, 152, 1997) suggest that breast cancer prognosis is
determined by p27 levels. Reduced levels of p27 predict a poor outcome for breast
cancer patterns.
Prokaryotes
Prokaryotic cells do not undergo mitosis. When the cell divides, the circular
chromosome replicates itself (DNA synthesis) and the cell pinches into two.
This process is called binary fission.