Q.State the Central Dogma of molecular biology as proposed by Francis Crick. What direction of information flow does it describe, and what does it say does NOT normally happen?

HIV, a retrovirus, uses reverse transcriptase to convert RNA to DNA, reversing the normal DNA-to-RNA flow of the central dogma.

The central dogma of molecular biology, as originally proposed, states that genetic information flows in one direction: DNA → RNA → protein (i.e., DNA is transcribed into RNA, which is translated into protein). This holds true for the vast majority of organisms, including Pea (a flowering plant), Mucor (a fungus) and Chlamydomonas (an alga) — all of which have DNA as their genetic material and follow the standard DNA → RNA → protein flow.

HIV (Human Immunodeficiency Virus), however, is a retrovirus whose genetic material is RNA, not DNA. Upon infecting a host cell, HIV uses a special enzyme, reverse transcriptase, to synthesise a DNA copy from its RNA genome (RNA → DNA), which is the reverse of the normal direction of the central dogma; this DNA is then integrated into the host genome and subsequently transcribed back into RNA and translated into viral proteins. This reversal — central to why HIV and other retroviruses were significant in revising the central dogma to a "central dogma reverse flow" — is why HIV does not follow the classical central dogma.