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VIRUS Notes Definition Viruses are tiny particles unlike any other organism. A virus consists of genetic material such as RNA or DNA wrapped in a protein coat. Characteristics of Life Homeostasis Nutrition Transport Respiration Synthesis Growth Excretion Regulation Reproduction Is a virus living? Is it living? No, because a virus can not reproduce on its own. It needs a host cells. How does a virus’ size relate to the size of the cell? Viruses are much smaller than a cell and that is why they can easily get into a cell How are viruses characterized? Characterized as: Plant virus Animal virus Bacterial virus (bacteriophage) What are the two parts that comprise a virus? Nucleic Acid Core (either RNA or DNA) Protein Coat called a capsid Shapes of Viruses 1. Rod shaped (tobacco mosaic virus) Shapes of Virus 2. Polyhedral (Mumps) Shapes of Virus 3. Helical (Herpes) How does a DNA virus replicate? DNA virus produces RNA (transciption) RNA directs production of viral proteins OR Viral DNA combines with host cell’s DNA (either plant or animal) How does RNA virus replicate or reproduce itself? Once inside the host, an RNA virus directs the host cell to produce proteins OR Viral RNA may make DNA Retrovirus Virus that has RNA as its genetic material Example is HIV Bacteriophage Virus that attacks a bacterial cell Two types of infection: A. B. Lytic Cycle Lysogenic Cycle Lytic Cycle Bacteriophage attaches to host cell and injects its DNA Foreign DNA produces more proteins in the host cell Causes cell to lyse (or break open) and the virus/phage is released into the host’s body Lytic Cycle Lysogenic Cycle Phage injects DNA into the host cell Foreign/phage DNA integrates itself into a chromosome Bacteria reproduces Lysogenic Cycle Lytic vs.Lysogenic Cycle