Biomedical Engineering Reference
In-Depth Information
TABLE 6.4
Random Motion—Measured Cell Speeds and Persistence Times
Cell Type
Speed
Persistence Time
Rabbit neutrophils
20
m
m/min
4 min
Rat alveolar macrophages
2
m
m/min
30 min
Mouse fibroblasts
30
m
m/h
1 h
Human microvessel endothelial cells
25-30
m
m/h
4-5 h
, the
length of time that the cell moves without changing its direction), and the orientation bias
(
Such a description is given in terms of the cell speed(s), the persistence time (
p
) that is due to action of chemoattractants. The random motility coefficient is related to
these parameters as
y
2
s
¼ s
p
ð
6
:
6
Þ
Typical values for these parameters are given in Table 6.4.
Cell Replication
THE CELL CYCLE
The process of cell division is becoming increasingly well understood in terms of molecu-
lar mechanisms (Figure 6.17). The so-called “cell cycle” of division is driven by a family of
regulatory proteins known as cyclin-dependent kinases (cdk proteins). The cyclins exist in
phosphorylated and dephosporylated states, basically a binary system. The network goes
through a well orchestrated series of switches, during which the cyclins are turned off and
on. When in an “on” state, they serve to drive the biochemical processes that are needed
during that part of the cell cycle. It should be noted that there are several important decisions
associated with moving “in and out of cycle,” which is the process of a cell moving from a
quiescent state (the so-called G o ) to a cycling (proliferative) state and vice versa. The cell cycle
G 2
Cdc2
S
M
Cdk2
cyclin B
cyclin A
G 1
cyclin E
Cdk2
FIGURE 6.17 Schematic representation of the eukarotic cell cycle (G1-S-G2-M) and the presence of cyclin-
dependent kinases.
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