Biomedical Engineering Reference
In-Depth Information
Fig. 2.37.
The Results of comet assay show that fragmented DNA that has a small
molecular size is easier to translocate from its original position than the intact and
larger DNA molecules.
A:
The absence of comet tail like trace of DNA without
ultrasound exposure meant that DNA was intact in the control condition.
B:
A
comet tail like DNA trace (the blurred image) from the position of the nucleus
means the existence of fragmented DNA in an ultrasound-treated cell
means immediate arrest of cell function, and cell death. If complete repair is
achieved, the damaged cell can survive as before. At the intermediate level
of ultrasound exposure, not severe enough to cause immediate death but
too severe for complete restoration, cells go into apoptosis. Necrosis means
a status of cell death. Apoptosis is another route to cell death, that can be
explained as programmed cell death.
In apoptosis, cell activity initiates a process of degrading the genomic
DNA into fragments. The sequence of apoptosis consists of three phases:
damage sensing, the initiation of degradation activity, and cell death with
morphological change. Initially, apoptosis has been found to be induced via
the stimulation of several cell surface receptors. Cell membrane alternations,
activation of enzymes, disruption of mitochondria, and DNA damage are
other possible key triggers of apoptosis.
A protein, p53, was initially introduced as a cancer suppressive factor. Its
function is regulation of the cell cycle. DNA damage results in phosphoryla-
tion of p53, which protects p53 from degradation. Accumulation of p53 arrests
the cell cycle at the G1 phase, which is the pre-phase of DNA synthesis for
mitosis. This regulation of the cell cycle plays a role in the time taken to
repair the DNA, before DNA duplication in preparation for cell proliferation.
Further accumulation of p53 molecules triggers the induction of apoptosis.
This means the abandonment of any effort to repair.
The accumulation of p53 was monitored by the expression of a manipu-
lated gene which is a fused gene of p53 and green fluorescent protein (GFP)
into a cultured cell. Then, we monitored p53 accumulation by measuring the
