Biology 1001A Chapter Notes - Chapter 23.1 - 23.4: Phylogenetic Tree, Hiv, Sub-Saharan Africa
23 Sep 2016
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Viruses are not shown on the tree of life because they lack many of the properties of life shared by all organisms and aren"t considered to be living organisms. *prof note: in fact, whether or not viruses are "alive" is a matter of scientific debate. 23. 1a, b); some capsids may be enclosed within an envelope derived from their host cell"s membrane (figure 23. 1c) are not cells, they don"t have cytoplasm enclosed by a plasma membrane. All viruses consist of nucleic acid surrounded by a protein coat, but they can have a very wide range of sizes and shapes. The nucleic acid genome of a virus may be either dna or rna and can be composed of either a single strand or a double strand of rna or dna. All viruses have genes that encode at least their coat proteins, as well as proteins involved in regulation of transcription. Some viral genomes also include virus-specific enzymes for nucleic acid replication.
