Central dogma exceptions

Under most circumstances genetic information flows from DNA (a) to RNA (b) to protein (c). DNA stores information that directs the synthesis of itself and the RNA molecules involved in protein synthesis. An important exception to the central dogma is the capacity of a small group of viruses, called the retroviruses, to synthesize DNA using an RNA template. 

Recall that according to the central dogma, the flow of genetic information is from DNA to RNA and then to protein. Retroviruses are an exception to this rule. The alterations of the central dogma that are observed in retroviruses and other RNA viruses can be illustrated as follows ... 

The process of RNA editing not only makes changes in the nature of protein but also presents an exception to the central dogma, it suggests because the direct transfer of information from DNA to RNA into protein. 

Figure 3.1 The Central Dogma of Molecular Biology. Black lines represent information transfers that occur frequently in cells. Blue indicates the exception of reverse transcription that occurs in some viruses, and RNA-directed RNA polymerase catalyzed RNA replication that also occurs in some plants and viruses only. Nucleic acids can be both stores and recipients of genetic information, whereas proteins are always recipients only of genetic information.

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