Download Cell Cycle Control System

• Checkpoints stop the
cycle until go-ahead
signal is received.
– There are 3
checkpoints (G1, G2, &
M) that must be
passed before Mitosis
is completed.
Cell Cycle
Control System
•
Molecules
associated
with
Cdks - cyclin-dependent kinase (kinase is an
enzyme that activates or inactivates by
the cell-cycle
phosphorylating (adding or removing Pi))
– cyclin is always present in the cell and is
clock
activated when phosphorylated
– synthesized during the S-phase
• MPF - M-phase promoting factor
–
–
–
–
partner molecule to Cdk
peaks during M phase and initiates Mitosis
aids in the disassembly of the nuclear lamina
switched off during Anaphase
• Growth factor (external regulator)
– secreted by near-by cells
– called a mitogen
– many allow the cell to proceed past
the G1 checkpoint
• if the go-ahead signal is not reached it
switches to the G0 phase
– most adult cells are at this position
Molecules
associated
with the
cell-cycle
clock
External controls
• density dependent inhibition
– cells stop dividing when overcrowded
• anchorage dependence
– to divide cells must be anchored
Cancer
• Cancer cells lack the inhibition pathways
– are immortal or stop at odd places in the
cycle
• HeLa cell line has been dividing since 1951
• usually 20-50 replications before cell death
– normal cells are transformed to cancer
cells through a transformation process
• Mutation in tumor suppressor genes
– Must mutate both copies of the gene
• Loss of function of p53 gene (apoptosis gene)
– if the cells stay in the same location they are
said to be benign
– if the tumor invades an organ and impair its
function, it is said to be malignant
– when the cancer cells travel to different
locations they are metastatic (process is
metastasis)