All viruses are made up of two kinds of substance.
First, all viruses contain proteins. Proteins are chemical
substances that occur in all living creatures. A particle,
or molecule, of a protein consists of a long chain of
substances called amino acids. There are about 20
different kinds of amino acid in proteins. These can be
arranged in any order on the protein chain. Different
kinds of plant or animal contain proteins with different
arrangements of amino acids. The protein generally
forms the outer coat of a virus. This outer layer of
protein encloses the second kind of substance found in
all viruses - nucleic acid.
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