Basic Chemical Nomenclature

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.

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