2 Characteristics of Viruses Among the smallest biological particles that are capable of causing diseases in living organismsConstructed of compounds associated with cells
3 Not Considered LivingA virus is not a bacteria, fungus, protist, plant or animal.They can not carry out cellular functions.A virus can not replicate without infecting cells and then using the organelles and enzymes of the cells of the host.
4 A Virus Has Two Essential Features A Nucleic AcidDNA orRNABut not bothA Capsid – a protein coat surrounding the nucleic acid.
5 Some may have a membrane like structure outside the capsid called an envelop Examples:InfluenzaChickenpoxHerpes-simplexHIV
6 Viral ShapeThe shape of the virus is determined by either its capsid or its nucleic acidTwo examples of shapeIcosahedron has 20 trianglular faces -- herpes simplex, chicken pox and polioHelix is a spiral shape( like DNA) -- rabies, measles and tobacco mosaic virus
7 There are Two Types of Viruses DNAReplicated in one of two waysDirectly produce RNA that make new viral proteinsJoin with the host cell’s DNA to produce new viral proteins
8 RNAViral RNA is released into the host cell’s cytoplasm and uses the ribosomes to produce new viral proteinsSome are known as retroviruses containing an enzyme called reverse transcriptase. These use the RNA as a template to make DNA. This DNA is integrated into the host cell’s DNA.
9 Viroid Smallest known particles able to replicate Short single strand of RNANo capsidDisrupts plant metabolism and may damage an entire crop
10 Prions Abnormal forms of proteins that clump in cells Linked to diseases of the brainConsist of 250 amino acids and not associated with any nucleic acidExamples:Scrapies in sheepMad Cow Disease in cattle
11 What is Mad Cow DiseaseMad cow disease, or bovine spongiform encephalopathy (BSE), is a fatal brain disorder that occurs in cattle and is caused by some unknown agent.Brain cells die leaving the brain of the cow to look like a sponge.It is believed to have come from a similar disease in sheep called scrapie.