Viruses

Structure of Viruses Viruses are infectious particles composed of nucleic acids enclosed in a protein coat (capsid) May also have a membrane envelope Nucleic acid may be double stranded DNA, single stranded DNA, single stranded RNA or double stranded RNA Dependent on the type of virus

Structure of Viruses Shapes of viruses can vary depending on accessory structures that help the virus infect its host

Viral Reproduction Viruses must have a host to reproduce because they lack metabolic enzymes and equipment for making proteins. Once the virus gets its genome into the host cell, it reprograms the cell to make more viruses. These new viruses can then be released to infect other host cells.

Reproductive Cycles of Phages Lytic Cycle Ends with the death of the host cell when the cell is lysed, releasing all of the phages produced Lysogenic Cycle Allows for replication of the phage genome without destroying the host Some phages are capable of both cycles, but some are only capable of the lytic cycle

Reproduction of Animal Viruses Can vary depending on the class/family of the virus Dependent on form of nucleic acid (often RNA) and presence of viral envelope Those animal viruses with a viral envelope will use it to enter the host cell Glycoproteins on the membrane attach to specific receptor molecules on the host cell

HIV: Human Immunodeficiency Virus Is a retrovirus (RNA is transcribed into DNA via reverse transcriptase) Viral DNA mingles with chromosomal DNA becoming a permanent part of the cell’s DNA

Treatments and Cures Antibiotics cannot be used because viruses lack metabolism Vaccines can be used to help the body fight pathogens prior to infection Antivirals can be used for some infections Usually HIV, herpes, influenza (A and B), hepatitis (B and C) Difficult to find antivirals that work without harming the host cell because of the way viruses work (i.e. replication by host cell and viral variation)

Treatments and Cures The damage done by a virus is related to the type of tissue it infects and damages Ex: Common cold infecting the respiratory tract is more easily repaired than polio infecting nerve tissues (mature nerve tissues do not divide) In some situations, long term impacts may require ongoing medical intervention