VIRUSES DO NOW Are viruses alive? List one reason why or why not.

Viruses are NOT alive! All viruses are composed of a core of DNA or RNA surrounded by a protein coat. They can range from a handful of genes to more than a hundred. They can vary in size and shape. Because viruses can’t reproduce themselves, they are not considered living cells. Many viruses are transmitted through body fluids. Some viruses like Influenza are able to spread in the air. Influenza Virus

Influenza Spherical in shape. Infects many people in the USA each year. Is usually only fatal in the very young, the very old, or individuals with suppressed immune systems. The exception was the deadly virus of 1918 where 30 million people died, many of whom were in their prime (21-29 years old).

Bacteriophage Bacteriophage infect bacteria cells. They have a piece of genetic material (DNA or RNA) surrounded by a coat of protein called a capsid.

Tobacco Mosaic Virus Infects only plants. It gets its name because it causes a mosaic pattern on infected plants.

How do viruses enter cells? Through the shape and structure of the its protein coat, the virus tricks cells by looking like other molecules that cells need. Because viruses need to attach to a specific protein in the host, they usually infect only one organism or closely related organisms. Viruses MUST infect a living cell to grow and reproduce. They have genetic material and can mutate They do not grow, use or obtain energy and do not respond to the environment

How do viruses reproduce? Viruses trick cells to allow its genetic material to enter. Once the DNA or RNA is in the host cell, the viruses DNA takes over the machinery of the cell turning it into a virus-producing machine. The cell manufactures viral DNA and protein coat. The virus can mutate during the process.

Lytic and Lysogenic Infection LyticLysogenic Injects DNA or RNA directly into host cell Cell makes mRNA from viral genetic material Cell mRNA is translated to make the protein coat to assemble new proteins. Viral proteins destroy the host DNA and cell. Infected cell will “lyse” or burst to release hundreds of new viruses. Injects DNA or RNA into host cell Viral DNA is incorporated into host DNA Virus is inactive during this time (prophage) It can stay inactive for many generations. Once active it enters the Lytic infection cycle.

Retroviruses Human Immunodeficiency Virus (HIV) is specific to infecting human T cells (part of the immune system). They contain RNA as their genetic material. Retroviruses produce a DNA copy of their RNA when they infect the host cell. This is considered a backwards process (usually its DNA copied to RNA), and that is how retroviruses get their name. They can remain dormant for a long time (years). They can be responsible for certain types of cancer (tumors), because retroviruses can contain a copy of the gene that tells the cell to stop making more cells.

Exit Slip  Which infection contains a prophage?  Is this the active infection or dormant?