The Cell - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 27

Initiate mitosis

Degradation

MCdk

M cyclin

M

Mitotic Cdk

Inactive Cdk

G2 G1

Inactive Cdk

S

S phase Cdk

Cell cycle

S cyclin

SCdk

Degradation

Initiate DNA replication

Figure 1.12 Role of different Cdk's during cell cycle.

1.8.2 Cell Division—M Phase/Mitosis
The M phase basically consists of the division of the contents of parental cells that
were replicated and synthesized during the preceding interphase. M phase is charac-
terised by the enormous changes in the cytoskeleton, their assembly and breakdown,
which serve to split the cytoplasm and replicate the genome into two parts. The M
phase is divided into mitosis and cytokinesis, and the mitotic phase by itself has five
subphases.
The most visible sign of the impending M phase is the appearance of condensed
chromosomes, made possible by the phosphorylation of histones. As discussed ear-
lier, histones are very crucial for the packaging and condensation of the threadlike
chromatin. Subsequent to this condensation is the formation of the bipolar spindle,
made up of microtubules and other associated proteins.
The centrosome comprising the centrosome matrix and pair of centrioles is the
structure involved with the nucleation of an array of microtubules. Before cell divi-
sion, the centrosome replicates to pass on the centrosome to its daughter cells. The
microtubules formed from the centrosome are of two types: polar and kinetochore