One does not need to be put
off by chemical nomenclature. The explication of alkylating agent for instance
is very easy
Carbon can form four bonds
the easiest example of which is methane, one carbon bound to four hydrogen
atoms (CH4). This molecule is called an alkane. The next one up in the
family of alkanes is ethane, two carbons attached to each other and each
baring three hydrogen atoms (for a total of six hydrogen atoms, C2H6).
Next up is propane; three carbon atoms and eight hydrogen atoms (C3H8).
And so on...
If to any of these molecules
you remove a single hydrogen atom you convert it from an alkane to an alkyl.
So if you remove one hydrogen atom from methane it becomes methyl by name
(-CH3, the dash before the C means there is a free bond available) ethane
becomes ethyl (CH3-CH2- The dash after the CH2 means there is a free bond
available), and propane becomes propyl.
These "one hydrogen missing"
species are not very happy and want their hydrogen back very quickly, failing
that they will attack and attach to anything that can provide as an alternative.
So an alkylating agent is one that loses one hydrogen and attaches to something
else. This something else can in turn be lost, for instance with cisplatin,
one other cancer chemotherapy agent, it happens to be a chlorine instead
of a hydrogen, but its the same story, the carbon loses a bond and wants
it back badly.
Alkylating agents are therefore
those that can give up a bond in their structure (in the case of cisplatin
it happens to be the bond between carbon and chlorine) and replace it with
a bond with the DNA molecule.
So the cisplatin behaves
as an alkyl species that gains a bond with DNA. Conversely DNA gains an
alkyl species.
Therefore DNA is said to
be alkylated by this process.
So cisplatin (or cyclophosphamide,
or chlorambucil, or thiotepa, and so forth) are acting as DNA alkylating
agents. HENCE THEIR NAME
There are many ways these
alkyl groups can attach; in some cases this leads to DNA bases not being
recognized by virtue that their structure is now different; in some more
complex cases DNA strands become crosslinked (the alkylating agent form
a bridge between DNA strands).
Basically these very reactive
alkylating agents break the harmony of the DNA structure in one way or
another. DNA damage and DNA breakage then often results and that leads
to a cell being unable to replicate its DNA properly which leads to cellular
crisis followed by cell death (programmed cell death, or apoptosis).
The word apoptosis is from
the greek, ptosis means fall, apo means separation, it did refer originally
to the biological process of self detachment and fall of the leave from
the tree.