The standard version of the
central dogma is the simple:
DNA --> RNA --> Protein
described above. However, some people think that this is an oversimplification of the situation. A truer picture is shown below :
_______
| |
__________|Protein|_____
| _____| | |
| | |_______| |
| | / \ |
| | /| |\ |
| | | | |
| | \ | | / |
|____|_______\| |/_______|____
| /| |\ | |
| / | | \ | |tRNA
| __| |__ | |ribosome
| | | | |translation
| | RNA |_____|____|
| | | |
| |_______| |
transcription | / \ |
| /| |\ |
| | | |replication
| \ | | |
|_______\| | |
/| | |
/ | | |
__| |__ |
| | \ | /
| DNA |____\_/
| ____ |
|_______| | |
/ \ | |
/| |\ | |
| |_______| |
|___________|
The problem here is the complexity of the representation. There are two types of arrow; big ones indicate 'transformations' while little ones indicate 'causation'. So the original dogma is pure transformation: from one type of molecule to another to another - the flow of information from DNA to protein. The second diagram (which I drew, but is almost certainly correct) subsumes the first - it is contained in the arrow between DNA and protein. However, the DNA is remade in the cyclic transform : both these processes are catalysed by protein.
You might argue that this is not what the central dogma should be about. That, however, is the point critics of dogmatic reductionism are trying to make (I think).
The whole picture is important.