Viruses are invisible to the naked eye. These microscopic entities, including coronaviruses, are responsible for a range of diseases. Scientific advancements in imaging technology have allowed researchers to peer into this unseen world, revealing their intricate structures. Understanding what a coronavirus looks like under powerful magnification provides insight into its biological makeup and how it interacts with its environment.
Visual Characteristics of Coronaviruses
Coronaviruses exhibit a distinctive spherical or irregular shape when observed through advanced microscopy. Their size ranges from 60 to 140 nanometers in diameter; for context, about 10,000 virus particles could fit within a single millimeter. The most striking feature is the presence of numerous spike-like projections that protrude from their outer surface.
These spikes create a halo or crown-like appearance around the viral particle, which is where the name “coronavirus” originates, derived from the Latin word “corona” meaning crown. The virus is encased within a lipid envelope, studded with structural proteins, including the prominent spike proteins.
Unveiling the Microscopic World
Visualizing objects as minute as coronaviruses requires specialized equipment beyond standard light microscopes. Traditional light microscopes are insufficient because the wavelength of visible light, which is around 400 nanometers, is too large to resolve structures. To overcome this, scientists rely on electron microscopes, which use beams of electrons instead of light.
Electrons, when accelerated to high speeds, behave like waves with much smaller wavelengths than light, enabling significantly higher magnification and resolution. Two primary types of electron microscopes are employed: Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM). TEMs pass electrons through thin samples to reveal internal structures, while SEMs scan the surface with an electron beam to produce detailed 3D images.
The Role of Spike Proteins
While visually prominent, spike proteins on the coronavirus surface serve a function in infection. These proteins act as the primary mechanism for the virus to attach to and enter host cells. The spike protein of SARS-CoV-2, the virus causing COVID-19, binds to a receptor on human cells called Angiotensin-Converting Enzyme 2 (ACE2).
This interaction is often described as a “key-and-lock” mechanism, where the spike protein is the key and the ACE2 receptor is the lock on the cell’s surface. Once the spike protein binds to ACE2, it undergoes structural changes that facilitate the fusion of the viral membrane with the host cell membrane. This allows the virus to release its genetic material into the cell and begin replication. This initial attachment and entry step, mediated by the spike proteins, is how coronaviruses initiate an infection.
Understanding Microscopic Visualizations
Images produced by electron microscopes are inherently grayscale. This is because electron detectors record variations in electron signals, not color information. To enhance clarity, highlight specific features, or make them more visually appealing, scientists often apply “false coloring” to these grayscale images using computer software.
False coloring involves assigning different colors to various structures or components based on their density or other properties, which aids in distinguishing them. Beyond these 2D images, scientists also create 3D models by compiling data from multiple electron microscope images. These models offer a more comprehensive and accessible view of the complex three-dimensional architecture of coronaviruses.