Wash your hands!: the Biochemistry of Soap

In the midst of the SARS-CoV-2 pandemic, the nation is busy stockpiling sanitisers and disinfectant sprays. Strangely enough, however, one of the most powerful weapons we have to fight the virus is also one of the most simple - ordinary household soap.

How does this staple household substance disintegrate viral particles?
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To better understand how the process works, we first need to look at the virus itself.

The virus' surface is a lipid membrane, embedded with proteins seen in the diagram above (membrane proteins, spike proteins, etc.). The proteins are crucial in allowing the virus to attach to certain surfaces in our body, and hence infect our cells. The inner genetic material (viral RNA) is released into our cells after protein attachment, allowing the virus to replicate using our cells as a host.

The lipid membrane is the most crucial to the virus' integrity - without a membrane, the protein and genetic information have no structure, and hence no way of transporting themselves throughout the body and into our cells. The membrane consists of two layers (a 'bilayer') of phospholipids, which are polar molecules that line up tail-to-tail, with their hydrophilic "heads" lining the surface of the membrane and hydrophobic "tails" tucked into the middle. This bilayer essentially forms the shape of the virus, keeping its proteins on the surface and its genetic material contained.

Similarly, soap comprises of molecules called "surfactants", whose structure bears a striking resemblance to phospholipid molecules in the viral membrane. Much like phospholipids, surfactants have a hydrophilic "head" group and a hydrophobic "tail".

Due to this structural similarity, surfactants can penetrate the viral membrane, accumulating to form a complex with the membrane's phospholipids. These complexes are called micelles, and are formed by the hydrophobic tails of surfactants and phospholipids lining up against each other to form globular structures.

These micelles are then lifted from the membrane's surface, breaking away significant parts of the bilayer with each micelle. Eventually, the virus' structure falls apart and it disintegrates entirely.