Viruses Dead or alive Viruses n What are

Viruses Dead or alive?

Viruses n What are the parts of a virus? n How does a virus replicate? n How do viruses benefit humans? n How do viruses cause disease?

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

Viruses n Viruses depend on the host cells that they infect to reproduce. n When found outside of host cells, viruses exist as a protein coat or capsid, sometimes enclosed within a membrane. (In other words they are dormant until they infect a cell. )

Viral structure n Viruses are not cells. n Basic structure: – Protein coat – Nucleic acid core (RNA or DNA) – Lipoprotein coat • (second coat – only in enveloped viruses)

Virus Categories n DNA viruses – stable, do not mutate rapidly – Single-stranded or doublestranded – Smallpox, Hepatitis B n RNA viruses – mutate rapidly, unstable – Single-stranded or doublestranded – HIV, Rhinovirus HIV Virus

Bacteriophages n attack bacteria (prokaryotes) n Typical phages have hollow heads (where the phage DNA or RNA is stored) n tunnel tails, n the tips of which have the ability to bind to specific molecules on the surface of their target bacteria.

Viruses n Viruses are found everywhere. are parasites responsible for causing many diseases in living things (herpes and HIV in humans, for example) n Viruses

Lytic Cycle n Virus attaches to host cell’s membrane and injects its nucleic acid into the host cell. n The viral nucleic acid takes over protein synthesis, creating new viruses. n The host cell bursts, lyses, releasing the newly formed viruses.

Before attachment Attachment Penetration and uncoating Release Assembly Replication

Lysogenic Cycle n Begins the same way as the Lytic cycle n Does not immediately take over the host cell’s genetic material n Instead – viral DNA is integrated (mixed) with the host cell’s chromosome n Cell is now called a Provirus.

Provirus n May not affect the functioning of the host cell n Every time host cell reproduces, so does the provirus – this can continue for many years n Can activate at any time causing illness

Retrovirus n Is the most complicated replication cycle n RNA viruses n Through reverse transcriptase, the RNA virus will make DNA from RNA within the host cell n This DNA is then integrated into the host cell’s DNA.

Common Viral Diseases n Lysogenic – Herpes simplex 1, herpes simplex 2, hepatitis B, chicken pox n Retrovirus – HIV – All other retroviruses are non-human affecting, although there is some debate

WORK… n. Complete the last diagram n. P. 480 lab 18. 1 problem solving n. P. 483 Q 1 -5