Ch 18 Viruses and Bacteria Viruses Nonliving particles

Ch. 18 Viruses and Bacteria

Viruses • • • Non-living particles that cause illness such as influenza. Composed of nucleic acids enclosed in a protein coat. Non-living Parasite? • • • Do not carry out respiration Do not Grow or Develop Can only reproduce with a host cell

Bacteriophage • • When a virus invades a bacteria Scarlet Fever • When a bacteria that causes Strep Throat gets infected or is infected by a bacteriophage.

Viral Structure • • • Inner core of RNA or DNA Protein coat called a Capsid Some have an additional coat called an envelope surrounding the capsid. • Envelopes are very similar to plasma membranes. • The proteins in the capsid determine the shape of the virus and can play a role in what cells can be affected and how the virus attaches to/infects a cell.

Attachment • • Must first recognize and attach to a receptor site on a plasma membrane of a host cell. Two ways of getting into a cell • Injection (non-enveloped viruses) • Engulfed (Enveloped viruses) • Plasma membrane of host cell engulfs the virus and creates a virus filled vacuole.

Replication • Lytic Cycle • Virus takes over the cell and it starts to produce new viral proteins and genetic material and assembles them into new viruses. • The viruses burst from the cell killing it. • Lysogenic Cycle • Inserts its genetic material into the chromosome of the host cell (provirus). • Every time the host cell replicates it also replicates the provirus. • At any time a cell infected with the provirus can go lytic and kill the host cell and further spread the disease.

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Proviruses • • Herpes – cold sores Chicken Pox - Shingles Hepatitis B Those infected with these viruses can go days, months or even years without symptoms utill one or more of the cells carrying the provirus go lytic.

Release of Viruses • • Lysis – The bursting of the host cell Exocytosis – (active transport process by which material

Retroviruses • • • Contain RNA and use the host cell and Reverse transcriptase to make DNA. Reverse Transcriptase- is an enzyme the virus contains that helps produce double stranded DNA from viral RNA. The double stranded DNA is then integrated into the host cell DNA.

HIV • • • Is a retrovirus that attacks human immune cells. Someone may have HIV for many years without getting sick because the virus is often in the lysogenic cycle. Producing new infected immune cells but not yet killing them. Once the virus goes lytic immune cells begin to die and HIV develops into AIDS.

Prions and Viroids • Prions • Proteins with NO genetic material that affect proteins around them and can cause disease. • Most common example is Mad Cow disease. • Viroids • A single circular strand of RNA with NO protein coat. • Have been found to cause disease in plants.

Terms to know form Contagion • • CDC – Center for Disease Control WHO – World Health Organization Encephalitis – swelling of the brain Antigen – anything foreign that enters the body and triggers and immune response. Pathogen – disease causing agent: something foreign that enters the body and causes illness. Antibody – A protein produced by the body that attaches to foreign substances so they can be removed. Incubation period – time period from when you come in contact with a pathogen to when you get sick.

More Terms • • • Fomite – an inanimate object that can transmit infectious agents. R – naught (R 0) – The contagiousness factor of a pathogen. Quarentine – separation of an area or population to contain the spread of a disease. Vaccine – injections of particles of viruses or bacteria that provide us with immunity. Attenuated – When a “live” virus or bacteria is used in a vaccine. The pathogen is altered to be harmless. Immunity – resistance to a pathogen, either from previous contact or a natural immunity because the individual already has antibodies.

Just a few more • • Epidemic – A widespread infection of a community. Pandemic – when an epidemic spread across country or across the globe. Cross over event – when a pathogen mutates and can now infect new species. Biological weapons – when a pathogen is weaponized.