# The Central Dogma of Information
## 6 Revisiting the Central Dogma of Biological Sciences  
Figure 5 is a reproduction of a manuscript by [PERSON] [47] in which the central dogma of molecular biology is first revealed. It is an attempt by [PERSON] to encapsulate the state of knowledge about DNA in a simple diagram, and to express it as \"Once information has got into a protein it can't get out again,\" where the \"arrows show the transfer of information.\" [PERSON] is referring to information as \"the sequence of the amino acid residues, or other sequences related to it.\" This view of information seems more in accord with [PERSON] (1948) than with the view of [PERSON] of information as \"a difference which makes a difference' [23]. In 1970, [PERSON] again reaffirmed the importance of the central dogma of molecular biology [46]. The central dogma of molecular biology relates to the transfer of information within a prokaryote cell. Figure 6 parallels the top drawing of Figure 5 and makes clear the various flows of information that are possible:  
* Three general transfers (DNA Replication, Transcription and Translation)
* Three special transfers (RNA Replication, Reverse Transcription and Direct Synthesis)  
Notice that Reverse Transcription is shown both in Figures 5 and 6a as tentative, as reflected by the discontinuous line arrow, but was later found to occur [48; 49; 50]. Figure 5: The central dogma of molecular biology [47]. Figure 6b parallels the bottom drawing of Figure 5 to show the flows of information that are not possible:  
* Three unknown transfers (Protein from Protein, RNA Synthesis and DNA Synthesis)  
Figure 6b is really an illustration of the central dogma of molecular biology, i.e., \"Once information has got into a protein it can't get out again.\"  
The use of the wording of 'Central Dogma' used by [PERSON] is unfortunate, since it initiated a long polemic discussed by [PERSON] [51] stating,  
\"In one aspect of the central dogma, [PERSON] was mistaken. In reality, the 'Central Dogma' was anything but a dogma. [PERSON] later claimed that he had not properly understood the meaning of 'dogma'--[PERSON] had to explain to him exactly what it meant. An indication of the truth of this assertion can be seen in the lecture when he states that the name that he has coined emphasizes the speculative nature of the idea--a dogma is not speculative. As [PERSON] later acknowledged, a more accurate description would have been 'basic assumption' [17]. This does not sound quite so sexy, but it would have removed a lot of subsequent misunderstanding. Perhaps if [PERSON] had not used such a dramatic turn of phrase, many subsequent critics would not have become so exercised about the question.\"  
Whatever the motivation of [PERSON], it certainly helped to focus the discussion on the transfer of information within the cell. In the end, it seems that if emphasis is placed on  
Figure 6: The central dogma of molecular biology: (**a**) The possible in genomic flow of information; (**b**) The impossible in genomic flow of information. what is not possible instead of what is possible, [PERSON]'s assertion is correct. To that effect [PERSON] [44] states,  
\"On the other hand, the discovery of just one type of present day cell which could carry out any of the three unknown transfers would shake the whole intellectual basis of molecular biology, and it is for this reason that the central dogma is as important today as when it was first proposed.\"  
One detail shown in Figure 6a,b that is not part of the hand-drawn sketches in Figure 5 is the added 'Cell Signals\" label which is representative of the ability of a cell to receive, process, and transmit signals from its environment and within itself [50]. Cell signals may be considered as the environmental effects that influence the transfer of information in the cell. This aspect is more pertinent to the discussion below that deals with a comparison between the two central dogmas of information and molecular biology.