Transcript VIRUSES
VIRUSES I. Structure A. Viruses are particles contain: 1. Nucleic acid (DNA or RNA) 2. Protein coat B. Viruses can reproduce only by infecting living cells. All viruses enter living cells and use the infected cell to produce more viruses. C. A capsid is the virus’ protein coat Special proteins on the capsid “trick” the host cell to let the virus in – Inside, virus genes get transcribed and translated into more viruses. – Host cell then bursts and is destroyed II. Types of Viruses A. DNA Viruses – DNA viruses contain DNA nucleic acid – More stable and less prone to mutation – Respond well to vaccination Ex: smallpox, chicken pox, herpes, HPV, Hepatitis B B. RNA Viruses – RNA viruses contain RNA nucleic acid – Prone to mutations – Require frequent vaccination Ex: Influenza, Hepatitis C, HIV, Rabies, Rotavirus, Yellow Fever Examples of Viral Disease Most colds caused by viruses Smallpox Shingles Different Hosts • Host cell is very specific – Animal hosts: rabies, HIV, chicken pox – Plant hosts: tobacco mosaic virus C. Viruses that infect bacteria are called bacteriophages III. Defense A. Vaccination offers protection for uninfected individuals – Work by stimulating production of antibody forms memory cells without causing disease • Vaccines are made from killed or weakened strains that cause antibody production but not the disease B. Antibodies • Proteins that recognize antigens (the invaders) and block their effects • When it locks with antigen, it flags it for death by white blood cells IV. How do Viruses Infect? 1) Virus injects nucleic acid into cell 2) Virus proteins and nucleic acids assemble into new viruses 3) Viruses break cell membrane and wall, releasing new viruses that attack other cells LYTIC CYCLE Lysogenic Cycle 1. Virus injects its DNA into host cell 2. Viral DNA integrates into the host DNA 3. A host cell makes copies of the virus every time it divides. The viral DNA embedded in the host’s DNA is called a prophage. VI. Retroviruses A. Define a retrovirus: Retroviruses contain RNA. Then make a DNA copy FROM their RNA. Then this DNA is inserted into the DNA of the host cell where it reproduces along with the cell until it enters the lytic cycle and spreads. B. H.I.V. (human immunodeficiency virus) C. A.I.D.S. (acquired immunodeficiency syndrome) VII. Are Viruses Living or Non-living? • They depend on living things • Most likely developed after living cells • First viruses may have evolved from genetic material of living cells • Cannot reproduce on their own