https://apologeticspress.org/APContent.aspx?category=12&article=1125
Biological Clocks: Evidence for a Clockmaker
[EDITOR’S NOTE: The following article was written by A.P. staff scientist Will Brooks, who holds a Ph.D. in Cell Biology from the University of Alabama at Birmingham.]
If one were to ask a clockmaker, “Could this device have constructed
itself?” the reply would most certainly be “No.” Clocks are complex
instruments designed to accurately and repeatedly keep time to the
millisecond. The complexity reaches all the way down to the system of
gears and shafts which drive the instrument. It would be inconceivable
even to consider the idea that such an instrument would evolve
naturalistically over time, eventually reaching a point when it is ready
to keep accurate time without missing a single second. Yet, this is
exactly what evolutionists would have us to believe regarding an even
more complex instrument, the cell division cycle—our own biological
clock. [NOTE: The following discussion of cell division is based on Alberts, et al., 2002.]
The cell division cycle is a coordinated sequence of events that drives the 
division
and reproduction of all cells from the single-celled amoeba to cells in
the human body. The complexity and coordination of this cycle is
staggering. The cell cycle is divided into four primary phases: G1, S,
G2, and M.
G1, or the Gap 1 phase, is the time in which cells carry out all of the
normal processes of the cell. Some cells remain in this phase for very
long periods of time. But, when appropriate stimuli are encountered by a
cell, a round of cell division is triggered. This point of no return is
known as the restriction point. Once a cell passes this point, it must
complete the entire cell cycle and return once more to G1. After a cell
reproduces, it must prepare for the next phase of the cell cycle:
S-phase or DNA synthesis phase. This preparation
requires activating countless genes and making many new proteins that
are used only during this one phase of the cell cycle. Once every
component is ready, S-phase may begin.
During the DNA synthesis phase, the cell must make an exact copy of its nuclear DNA.
This duplication is important because both new cells that will result
from cell division must contain equal and identical copies of the
parental cell DNA. One human cell contains roughly four billion base pairs of DNA. Copying all of this DNA without error is no small task, yet the cell does so incessantly.
Following completion of DNA synthesis, the cell
enters the second gap phase, G2. During this period, the cell prepares
for physical division, which involves the production of a whole new set
of proteins. At the same time, all those proteins used during S-phase
are degraded, since they are no longer needed, and their presence would
only promote more DNA synthesis. After all the
proper proteins are made and degraded, the cell is ready for physical
separation, which takes place during mitosis or M-phase.
Mitosis involves the separation of chromosomes, followed by the
separation of the cell. Human cells have 46 pairs of chromosomes when
they enter mitosis. Each pair must be separated in the appropriate way
in order for each daughter cell to have two copies of the 23 human
chromosomes. Once again, this is no small feat. Even one mistake leads
to abnormal chromosome numbers in the daughter cells and is
harmful—often lethal—to the cell. Yet, the cell achieves this separation
without error over and over. At the conclusion of mitosis, two cells
result, each identical to the other. Both cells are now once more in
G1-phase, able to enter another round of cell division. This cycle is
repeated time after time, like clockwork.
In a physical clock or watch, a system of gears and shafts are designed
to keep the clock moving, keeping precise, accurate time. What are the
driving forces, the gears and shafts if you will, of the cell division
cycle? Our cells have their own mechanism for keeping things moving. Two
families of proteins lie at the heart of cell cycle progression. They
are called cyclins and cyclin-dependent kinases (Cdks). These two groups
of proteins work in a cooperative manner to promote each action that
takes place during the cell cycle. How they work to keep the biological
clock ticking is amazing!
Cyclin-dependent kinases function as enzymes, with the ability to link a
small phosphate group (-PO4-3) onto a variety of proteins. This linkage
serves as an “on” switch for the targeted protein. By phosphorylating
(linking a phosphate) to proteins in the cell, Cdks work to turn on and
off other proteins that play roles in the cell cycle. But, Cdks
themselves need an “on switch,” which comes from the cyclin proteins.
Cyclins are able to bind to cyclin-dependent kinases in order to form a
stable protein complex between the two. Once bound together, Cdks are
free to phosphorylate their repertoire of targets to promote all the
activities of the cell cycle.
It might seem, then, that all cyclins and Cdks are active all of the
time and throughout the cell cycle, but they are not. This is where the
clockwork activity of the cell is truly seen. During each phase of the
cell cycle (G1, S, G2, and M), a different set of cyclin and Cdk
proteins are active. Therefore, each pair of proteins is able to promote
only those activities which should occur during a phase. For example,
during the DNA synthesis phase (S-phase), only those proteins that play a role in making new DNA
are activated. This action prevents the phases from occurring out of
order or at the wrong time. But, how is only one pair of cyclin-Cdk
proteins active at a time? The answer comes in the form of another
cyclical event.
Unlike the Cdk proteins, which are always present in the cell, cyclin
proteins come and go in a cyclical manner—which accounts for the name
cyclin. Production of these proteins is coordinated with the cell cycle
phases. When a cell receives signals to undergo division, the G1-cyclins
are expressed by the cell. They then partner with G1-Cdks, which
already are present to promote those G1 activities of the cell.
Additionally, G1 cyclin-Cdks initiate expression of the next group of
cyclins—the S-phase cyclins. Once expressed, S-phase cyclin-Cdk partners
promote activities of S-phase and turn on the G2-cyclins. This cycle
continues for each phase of the cell cycle. Figure 2 illustrates this
feature by showing the levels of S-phase cyclin throughout the cell
cycle.
This amazing process of cyclin expression is also coupled with cyclin
destruction. Once a new cyclin is present in the cell, the previous
cyclin is destroyed, which effectively ends the previous cell cycle
phase. This constant repetition of cyclin protein production and
destruction is the driving force behind every event in the cell division
cycle.
Together, the cell cycle and the cycle of cyclin protein
production/destruction are an amazingly designed system of events. Such
complexity is inexplicable on the basis of naturalism. In this case, the
clockmaker is the intelligent Designer, God. It would be impossible for
a six-foot-tall grandfather clock or even a small watch to construct
itself gradually and start ticking. Equally impossible, the cell could
never appear, ready to “tick” through the highly coordinated process of
cell division. Just as clocks are constructed by an intelligent
designer, the cell cycle is clear evidence for intelligent design in the
Universe.
REFERENCE
Alberts, Bruce, et al. (2002), Molecular Biology of the Cell (Oxford: Garland Science).
