Viruses

Viruses - The Boundary of Life At the boundary of life, between the macromolecules (which are not alive) and the prokaryotic cells (which are), lie the viruses and bacteriophages (phages).

Living or non-living? Like non-living: do not respond to stimuli do not respire do not grow do not do any of the things we normally associate with life. Like living: Contain nucleic acids Made of protein Do mutate can reproduce at a fantastic rate but only in a host cell.

Viruses are found everywhere. 1898, Dutch botanist Martinus Beijerinck discovered sub-microscopic particles that caused infectious diseases He called them viruses (Latin for poison) These twilight creatures are parasites responsible for causing many diseases in living things, including animals, plants, and even bacteria (herpes and HIV in humans, for example). Viruses are found everywhere.

They may be rod-shaped, spherical, polyhedral, or with a head and tail.

The Structure Of a Virus Viruses are composed of a core of nucleic acid The Nucleic acid core is surrounded by a protein coat called a capsid The Nucleic core is either made up of DNA or RNA but never both

Viruses and bacteriophages invade cells and use the host Viruses cannot grow or reproduce unless they enter the body of some living organism  are parasites Viruses and bacteriophages invade cells and use the host cell's machinery to synthesize more of their own macromolecules. Terms: Bacteriophages attack bacteria (prokaryotes) Viruses attack eukaryotic cells.

Once inside the host the bacteriophage or virus will either go into a Lytic Cycle - destroying the host cell during reproduction. OR Lysogenic Cycle- a parasitic type of partnership with the cell Term: Viruses that kill their host cells are known as virulent

The Lytic Cycle

The Lysogenic Cycle

Cycle of Lytic and Lysogenic

A provirus is a DNA virus that has been inserted into a host cell chromosome.

A retrovirus injects the enzyme, reverse transcriptase into the cell to copy viral RNA into DNA.

HIV is a retrovirus injecting the enzyme, reverse transcriptase into the cell to copy viral RNA into DNA.

Viruses are host specific (viral or host specificity): a protein on the surface of the virus has a shape that matches a molecule in the plasma membrane of its host, allowing the virus to lock onto the host cell.

HIV doesn’t target just any cell, it goes right for the cells that want to kill it. “Helper" T cells are HIV's primary target. These cells help direct the immune system's response to various pathogens.

HIV undermines the body's ability to protect against disease by depleting T cells thus destroying the immune system. The virus can infect 10 billion cells a day, yet only 1.8 billion can be replaced daily.

After many years of a constant battle, the body has insufficient numbers of T-Cells to mount an immune response against infections. At the point when the body is unable to fight off infections, a person is said to have the disease AIDS. It is not the virus or the disease that ultimately kills a person; it is the inability to fight off something as minor as the common cold.

Our immune system’s defence against viral infections Phagocytic cells – cells in our blood that recognize and destroy foreign substances by engulfing them Production of antibodies – antibodies deactivate and remove a virus from infecting host cell Vaccines – a substance that triggers an immune response and causes the body to produce antibodies without causing the illness Many are produced from killed or weakened viral particles, or synthetically produced