Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Ch 24 Characteristics of Viruses Viruses are not alive and they are not cells. Viruses ARE – Nonliving particles that cause disease (Flu, HIV, colds, warts) Do not exhibit all criteria of life such as growth and development. Once inside a host cell…they exhibit two characteristics of life They replicate/reproduce inside a host cell. Heredity & are able to mutate. Viruses are named after the diseases they cause or the tissues/organs they infect. bacteriophage –viruses that infect bacteria cells Structure of Viruses Capsid-outer protein coat Inner core- DNA or RNA contains instructions for copying viruses. The tail and tail fibers help viruses bind to the host cell Envelope – outer coat with a structure similar to the plasma membrane. Only on some viruses. Bacteriophage Kinds of viruses How do viruses attack? Viruses recognize and attach to a receptor site on a host a virus latches onto a host cell with its “tails”. Viruses are species and cell specific. This prevents the spread of disease. Viruses just attack one particular kind of cell. (HepB & Liver Cell) Viruses inject their genetic material DNA/RNA into the host cell. An enveloped virus is engulfed by the host cell then burst the vacuole to release nucleic acid into the host Lytic cycle Viruses take over the metabolic activities of the host cell. The host cell’s energy, enzymes, and organells are used to replicate viral genes and new virus particles are produced. Once the DNA of the virus is inside the cell, it takes control of it and forces it, using its resources, to produce more of the same virus DNA and parts of the virus. The new virus particles burst out of the host cell and then infect other cells. When most of the cell is used up to produce more virus material, it becomes is so weakened that it bursts like a soap bubble, releasing the new replicated viruses which immediately seek out new host cells to invade and destroy. 5 Step Process: A. Attachment B. Entry C. Replication D. Assembly E. Release Attachment Lysis and Release Entry Assembly Replication Lysogenic Cycle Replication cycle in which the virus’s nucleic acid becomes part of the host cell’s genetic material. Viral DNA that is integrated into the host cell’s chromosomes is called a provirus or temperate virus. The host cell will continue its activities. (Growth & Replication) Virus replicates along with the host cell. Lysogenic cycle can continue for years until the provirus/temperate virus is activated and enters a lytic cycle. Examples: HSV1 – Cold Sores; HSV2 – Genital Herpes; HepB; Chicken Pox/Shingles Lysogenic Cycle Viruses exit host cell and infect other cells. Lysis-viruses burst from cell killing the cell in the process Exocytosis-secreted from cell by active transport Examples of Proviruses the virus that causes chickenpox reactivates to cause shingles Retrovirus Virus that contains the genetic material RNA rather than the more common DNA Viral RNA is converted into DNA by reverse transcriptase. When a retrovirus infects a cell, it injects its RNA into the cytoplasm of that cell along with the reverse transcriptase enzyme. Retroviruses then become provirus. HIV Lysogenic Stage Provirus, retrovirus Affects White Blood Cells Released into the bloodstream by exocytosis WBC’s fight disease; decrease in WBC’s leads to the inability to resist disease. People do not appear sick and pass to others Onset of AIDS when cells enter lytic cycle and WBCs are killed Tumor viruses (RETROVIRUS) Cause normal cells to become tumorous Warts – Human Papilloma Virus Cancer Human Popilloma Virus – Cervical Cancer Hepatitis B virus-liver cancer Epstein-Barr Virus – Burkits Lymphoma Human T-Lymplotrophic Virus - Lukemia Plant Viruses 400 identified plant viruses 1000 plant diseases All are not harmful Some cause changes in coloration. Tobacco mosaic virus causes yellow spots on tobacco plants Other plant viruses cause patterns of color on some plants Diseases caused by viruses Rhinovirus-common cold Herpes zoster virus-chicken pox Polio virus-polio (paralysis) HIV/AIDS Measles Mumps Hepatitis Herpes