The virion is mainly composed of nucleic acids and proteins. The core is nucleic acid, and there is a protein shell around the nucleic acid, called capsid. The capsid and nucleic acid together are called the nucleocapsid. Some viruses are surrounded by an envelope outside the nucleocapsid. The shell is composed of a certain number of shell particles. Each shell particle is composed of one or more peptide molecules and collected by medical education network.
According to the arrangement of the shell particles, the virus capsids have the following types of symmetry: spiral symmetry; 20-hedron stereo symmetry and compound symmetry. The envelope is obtained when the virus is released to the outside of the host cell by budding during the maturation process, so it contains the chemical components of the host cell membrane or nuclear membrane. Some envelopes have protein-like spikes on their surface, called capsule grains or spikes.
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