COVID-19 is an illness that emerged in late 2019, caused by the microscopic SARS-CoV-2 virus. Understanding what these tiny entities look like requires specialized scientific tools and techniques. The visual characteristics of the SARS-CoV-2 virus offer insights into its classification and how it interacts with human cells.
Seeing the Unseen
Visualizing objects as minute as viruses presents a significant challenge because they are far smaller than the wavelength of visible light. Traditional light microscopes, which use light to illuminate and magnify specimens, cannot resolve structures below a certain size.
Scientists therefore rely on electron microscopes, such as the Transmission Electron Microscope (TEM) and the Scanning Electron Microscope (SEM), to overcome these limitations. Instead of light, these instruments use a beam of electrons, which have much shorter wavelengths, to create highly magnified images. The electron beam interacts with the specimen, and detectors then translate these interactions into an image.
SARS-CoV-2 particles typically measure between 60 and 140 nanometers in diameter. To put this into perspective, a human hair is about 80,000 to 100,000 nanometers thick, and even bacteria are significantly larger, often measuring hundreds to thousands of nanometers. Electron microscopes can magnify these tiny structures millions of times.
The Signature Look of SARS-CoV-2
Under the powerful magnification of an electron microscope, the SARS-CoV-2 virus typically appears as a roughly spherical particle. Its most distinctive feature is a series of club-shaped projections that protrude from its surface. These projections are known as spike proteins, and they are arranged in a way that gives the virus a crown-like, or “corona,” appearance.
This crown-like morphology is the origin of the term “coronavirus” for the family of viruses to which SARS-CoV-2 belongs. Beyond the spike proteins, the viral surface also features other proteins, such as the envelope (E) protein and the membrane (M) protein, which contribute to the virus’s structural integrity. The spike proteins are particularly significant because they act as keys, binding to specific receptors on the surface of human cells, thereby facilitating the virus’s entry and infection process.
Their shape and arrangement are unique to SARS-CoV-2, differentiating it from other coronaviruses. The internal structure, encased within the spherical shell, contains the virus’s genetic material, RNA, coiled with nucleocapsid proteins.
Understanding What You See
The captivating images of SARS-CoV-2 that are commonly shared are typically generated using electron microscopy. Electron microscopes do not produce images in color. The detectors in these microscopes capture variations in electron scattering, resulting in grayscale images that show differences in density and topography.
The vibrant colors seen in many published images are added digitally during post-processing. This technique, known as “false-coloring,” is applied to highlight specific structures, differentiate components, and make the images more accessible and interpretable for a broader audience. For instance, spike proteins might be colored red, while the viral membrane is blue.
Furthermore, these images are often representations, not live photographs of the virus in action. Many are two-dimensional cross-sections, providing a slice-through view of the particle. Others are three-dimensional reconstructions, built from multiple two-dimensional images or computational modeling, to offer a more complete spatial understanding of the virus’s architecture. These visual tools aid researchers studying viral structure and communicating complex scientific information to the public.