| Figure 2. Genetic alterations
and disorganized chromosomes (the linear strands of DNA on which genes
lie) are seen frequently in cancer cells.
The substitution of one of a
gene’s constituent nucleotides for another can sometimes contribute to
carcinogenesis. The altered gene can sometimes code for a corrupted
protein that functions poorly or not at all, which in turn can alter the
growth characteristics of the cell.
In panel a the normal sequence calls
for a cytosine nucleotide (designated C), paired with a guanosine
nucleotide (designated G).
Inside a tumor cell the sequence for this gene
has become altered such that thymine (designated T) is found in place of
C, and adenosine (designated A) is partnered with it.
Sometimes genes are
amplified, becoming overabundant on the chromosomes of cancer cells
(b), when compared with normal cells. Amplified genes can sometimes
lead to the over-manufacture of the proteins they encode, which can alter
cellular growth patterns. Other genetic anomalies arise as a result of
translocation (c), in which a portion of one chromosome becomes
exchanged for a section of another. This can place genes on sections of
translocated chromosomes under abnormal regulatory control.
Genes of plant
and animal cells can also come under abnormal genetic control following
the insertion of genetic material by some viruses (d).
All these
conditions can lead to abnormal cellular growth. |
