The smallest known form of life is typically considered to be a cell, which is comprised of numerous atoms and various biomolecules. However, if we shift the focus to self-replicating structures, things become more complex.
The definition of "self-replicating structure" can vary depending on the context. In the realm of synthetic biology and molecular self-assembly, scientists have designed and created small, artificial structures capable of self-replication. For instance, researchers have developed DNA-based nanostructures that can undergo replication processes. These nanostructures consist of a relatively small number of atoms, typically in the range of thousands to tens of thousands.
Naturally occurring self-replicating structures, such as viruses, can also be smaller than a cell. Viruses are considered the simplest and smallest biological entities capable of self-replication. They consist of genetic material (either DNA or RNA) enclosed in a protein coat. While the specific size of viruses can vary, they typically range from around 20 to 400 nanometers in diameter. Since atoms make up molecules, and molecules make up viruses, it's safe to say that viruses contain significantly fewer atoms than the smallest known life form.
It's important to note that our understanding of self-replicating structures is continually evolving as scientific research progresses. The boundaries of what constitutes a self-replicating structure and the smallest possible size are still areas of active investigation.