AGE OF VIRUS

The much-scorned, dreaded biological entities are also the highly misunderstood beings

- SNIGDHA DAS, BANJOT KAUR AND ISHAN KUKRETI

ONCE UPON a time, just as life was taking shape on Earth, there was a free-roaming cell. It was fiercely independent. As time passed, it developed an intimate relationship with another of its kind, which predated LUCA—the last universal cellular ancestor. In the beginning, the relationship was symbiotic. But over the period, as the forefather of LUCA embarked on a journey to acquire complex traits, the primitive roamer opted for a simpler, parasitic life. So much so, that one by one it started renouncing its genes, essential for supporting life, until it was left with a few strands and became indistinguishable from the nonliving. Eventually it was unable to replicate independently and accepted the fate of an obligate intracellular parasite—a virus.

Some scientists would like to narrate this story, of the origin of virus, a little differently. They would like to start from the forefather of LUCA that possessed mobile genetic elements—pieces of genetic material capable of moving around within a genome. This characteristic continues to be part of the modern cell; in fact, in humans about 50 per cent of the genome is thought to be mobile elements. At some point, some of the genome of this primordial cell—forefather of LUCA—acquired a few structural proteins and gained the ability to exit the cell and spread as an infectious agent, or a virus.

Both the narrations are based on the assumption that cells existed before viruses. What if it’s the other way round? Some scientists postulate a scenario in which viruses existed in a pre-cellular world as self-replicating genetic elements—RNS (ribonucleic acid) or DNA (deoxyribonucleic acid) molecules. Over time these units, became more organised, complex and even synthesised proteins required for the formation of their shell, known as capsid.