What is a Virus? • A small infectious agent that can replicate only inside the cells of other organisms, bacteria, plants or animals. • Consists of at least two of three parts • Genetic material, DNA or RNA (retro virus) • Protein coat that protects the genetic material • Possible lipid membrane
How do they compare to Bacteria? • They both can cause disease and have a similar structure
Are viruses alive? • Viruses have characteristics that may classify them as living. • They also have characteristics that classify them as non-living • They have no metabolism and cannot reproduce on their own so they do not qualify as a living organism.
How small are viruses? • Viruses are typically 20 – 400 nm • Bacteria are typically 1000 nm
4Shapes of a virus • Helical
Virus discovery and origin • In 1884 by French microbiologist Charles Chamberland • Origin is unclear because they do not leave behind any fossils or life evidence • The viruses that have been preserved by scientists date back about 90 years • There are 3 different theories of possible origin
1. Regressive • Viruses may have been small cells that parasitized larger cells and then lost unnecessary genes • 2. Cellular • May have evolved from bits of DNA, RNA or plasmids that may have escaped or been lost • 3. Coevolution • May have evolved from complex proteins and genetic material at the same time as cells first originated and are dependant on cells to stay in existence