Question

Explain the importance of evolution in the recent appearance of SARS-CoV-2. Your answer should demonstrate that you understand the concept of evolution and related concepts covered in the course.

Answer 1

• To be clear, SARS-CoV-2 is not the flu. It causes a disease with different symptoms, spreads and kills more readily, and belongs to a completely different family of viruses. This family, the coronaviruses, includes just six other members that infect humans. Four of them—OC43, HKU1, NL63, and 229E have been gently annoying humans for more than a century, causing a third of common colds. The other two—MERS and SARS or “SARS-classic” as some virologists have started calling it) both cause far more severe disease.

• The structure of the virus provides some clues about its success. In shape, it’s essentially a spiky ball. Those spikes recognize and stick to a protein called ACE2, which is found on the surface of our cells: This is the first step to an infection. The exact contours of SARS-CoV-2’s spikes allow it to stick far more strongly to ACE2 than SARS classic did, and “it’s likely that this is really crucial for person-to-person transmission” says Angela Rasmussen of Columbia University. In general terms, the tighter the bond , the less virus required to start an infection.

  There’s another important feature. Coronavirus spikes consist of two connected halves, and the spike activates when those halves are separated only then can the virus enter a host cell. In SARS classic, this separation happens with some difficulty. But in SARS-CoV-2, the bridge that connects the two halves can be easily cut by an enzyme called furin, which is made by human cells and crucially is found across many tissues.

• SARS-CoV-2 seems to infect both upper and lower airways, perhaps because it can exploit the ubiquitous furin. This double whammy could also conceivably explain why the virus can spread between people before symptoms show up a trait that has made it so difficult to control. Perhaps it transmits while still confined to the upper airways, before making its way deeper and causing severe symptoms. All of this is plausible but totally hypothetical; the virus was only discovered in January, and most of its biology is still a mystery.