Download Cell Cycle Control System

Cell Cycle
Control System
Chapter 12.3
Its
Time to
Play
Simon Says!!
Molecular Control system
• Timing and rate of cell division in different
parts of the plant and animal are crucial to
normal growth, development, and
maintenance.
• Frequency varies among different types of
cells
– Ex: Frequent divisions of skin cells
Liver cells reserve as need arises
Nerve and muscle cells don’t even divide
Cytoplasmic signals
• 1970s experiments
revealed that
molecular signals
from the cytoplasm
were driving the cell
cycle.
Cell Cycle Control System
A cyclically operating set of molecules in the cell
that both triggers and coordinates key events in
the cell cycle.
Other Examples
• Take a minute. Can
you think of more
examples of control
systems?
Cycle Control System
• Checkpoints are critical control points where
stop and go ahead signals regulate the cycle.
• Some cells have built in stop signals that halt
the cycle until another signal overrides and
starts cycle.
• Checkpoints can register signals from both
inside and outside the cell
Checkpoints
• Three major
checkpoints:
G1 – the restriction
point
G2 –MPF facilitates to
cell dividing stage
M – mitotic division
Regulatory Molecules
• Protein kinases enzymes that activate or
inactivate proteins by phosphorylating them
• Cyclins are proteins that cyclically fluctuate
their concentration in the cell
*determine active or inactive state of
kinases.
• CdK – cyclin-dependent kinases in varying
numbers control all stages of cell cycle
Internal Checkpoints
• G1 phase – activator CdK will cause cycle to
complete itself; whereas lack of cyclins will
halt in G0 phase
• G2 phase – MPF “ M-phase promoting factor”
will trigger passage to mitosis or cell dividing
phase.
• M phase – kinetochores send signal that
delays anaphase until all chromosomes are
attached to spindle
External Checkpoints
Growth factors – protein released by cells that
stimulate other cells to divide
*mitogen – mitosis promoter
PDGF – made by platelets; required
for division of fibroblasts to clot
(G1 phase)
Density dependent inhibition – occurs when
crowded cells stop dividing
*results from physical contact, and lack of
adequate growth factors and nutrients
Anchorage dependence – cells must be attached to
a substratum such as extracelluar matrix;
cytoskeleton attachment
Cancer Cells
• Cancer cells divide
excessively and invade other
tissues.
• Cancer cell do not respond to
most of the body’s control
mechanisms.
• Cancer cell still grow even
when growth factors have
been depleted.
• Cancer cells stop dividing at
random points of the cycle.
Cancer Cells
Transformation – process that converts a normal cell to
a cancer cell
Tumors:
benign – remains at original site
malignant – invades other organs and impairs
function
Cancer Cells
Metastasis- spread of cancer cells to locations
distant from original site.
*cells can secrete signal molecules that
cause blood vessels to grow toward tumor
*cells can also separate and travel in blood
and lymph to other parts of the body
Treatments
Radiation – localized tumors or proliferation
*targets and damages DNA of cancer cell
Chemotherapy – malignant or metastasis
*most target and prevent cells from proceeding
past metaphase
*side effects – exerts same targets on
normal cells
Ex: intestinal cells - nausea
hair follicle cells – hair loss
immune cells - increased infections