Chapter 18
The Genetics of Viruses
The Connection Between Genes and Proteins
1.
Adolf Mayer, Dimitri Ivanowsky, Martinus Beijerinck, and Wendell Stanley all
helped to discover viruses.
2.
Viruses are made up of nucleic acid, DNA or RNA, and are enclosed in a protein
coat, the capsid, and sometimes further wrapped in a membranous envelope. The
individual protein subunits making the capsid are called capsomeres. Although
diverse in size and shape, viruses have common structural features.
3.
Viruses are intracellular parasites because they mess up the cell. They attach to it
and make it so the cell will make more viruses.
4.
The virus identifies a host cell by the cell’s receptor molecules.
5.
Bacteria use restriction enzymes against phages.
6.
Lytic reproductive cycle is when the virus uses the cell to produce the virus DNA
inside the cell then the new viruses are made when they leave the cell. In the
lysogenic cycle, the virus enters the cells and makes copies of itself in the cell.
Then the new viruses assemble in the cell and lyse.
7.
The glycoproteins on the viral envelope bind to specific receptor molecules on the
host cells, promoting viral entry into the cell. The capsid and viral genome enter
the cell. Digestion of the capsid by cellular enzymes releases the viral genome.
The viral genome functions as a template for synthesis of complementary RNA
strands by a viral enzyme. New copies of viral genome RNA are made using
complementary RNA strands as templates. Each new virus buds from the cell. Its
envelope is studded with viral glycoproteins embedded in membrane that are
derived from the ER. A capsid assembles around each viral genome molecule.
Vesicles transport envelope glycoproteins to the plasma membrane.
Complementary RNA strands also function as mRNA, which are translated into
both capsid proteins and glycoproteins for the viral envelope.
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