Viruses Notes PDF - Biology

Ch 2.2 Viruses Viruses are not part of the 6 kingdoms because they are not alive. It is thought that viruses are perhaps the most ancient form of life, or escaped fragments of DNA that once formed part of living cells. Characteristics: ​genetic material surrounded by a protein coat ​depend on a...

Ch 2.2 Viruses Viruses are not part of the 6 kingdoms because they are not alive. It is thought that viruses are perhaps the most ancient form of life, or escaped fragments of DNA that once formed part of living cells. Characteristics: ​genetic material surrounded by a protein coat ​depend on a host cell for respiration, nutrition and reproduction ​act as intracellular parasites ​much smaller than bacteria (hundreds of thousands can fit inside a cell) ​viruses are cell specific (ie// plant viruses only attack plant cells) ​geometrically shaped Examples: A bacteriophage is a virus that infects bacterial cells by injecting its DNA and replicating within the bacterial cell. Viral Reproduction: Viruses can reproduce two ways – the lytic cycle and the lysogenic cycle. ​Lytic cycle – viruses are replicated within a host cell and released. ​Lysogenic cycle – viral DNA is replicated along with the host cell’s DNA for many generations. These cells can then enter the lytic cycle, releasing exponentially more new viruses. Disease Protection: While antibiotics can be taken to kill bacterial diseases, viruses cannot be cured by antibiotics, since they only target bacterial cell structures. Viruses are hard to kill for various reasons, one being that they aren’t alive in the first place. The best way to protect yourself against viruses is to be vaccinated. ​Vaccines prevent viral diseases. ​Vaccines are altered forms of a virus (same shape, but cannot cause disease) ​The body’s immune system recognizes the specific shape and creates antibodies against the virus that stay in the body for many years. ​If they body is ever exposed to the real virus, it is already protected against and no disease symptoms will occur. ​Viruses are always changing, so new vaccines need to be created every year. You cannot get sick from a vaccine, but you may react slightly (inflammation, tenderness) to the foreign material injected. Virus-like Particles: ​ Prions – abnormally shaped, infectious brain proteins responsible for some rare diseases. ​ Viroids – very small infectious pieces of RNA (genetic material that provides instructions for making proteins) that do not have a capsid. Homework pg 59 #1-8.