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Illustration of SARS-CoV-2 virus particles. SARS-CoV-2 is an enveloped RNA (ribonucleic acid) virus. The surface of this virus consists of a lipid membrane (yellow) and 3 protein types embedded in the membrane. These protein types are: spike (S) protein trimers (red/orange/blue/green), envelope (E) proteins (bright brown), whose main body is hidden within the membrane and which protrudes a short distance outwards and about 900 dimers of the membrane (M) protein (darker brown), which are also mainly hidden in the membrane and which end directly at the lipid surface. Spike proteins allow the virus to bind to the host cell. Membrane proteins and envelope proteins play a role in virus assembly. SARS-CoV-2 causes the respiratory infection Covid-19, which can lead to fatal pneumonia. (KEYSTONE/SCIENCE PHOTO LIBRARY/BURKHARD RAMMNER / SCIENCE PHOTO LIBRARY)