VIRUSES

A. Viruses are particles containing: 1. Nucleic acid 2. Protein coat B. They can reproduce only by infecting living cells! cells! I. Structure

All viruses enter living cells and use the infected cell to produce more viruses. C. A capsid is the virus ’ s protein coat

D.Special proteins on the capsid “ trick ” the host cell to let the virus in cell to let the virus in Inside, virus genes get transcribed and Inside, virus genes get transcribed and translated into more viruses translated into more viruses Host cell then bursts and is destroyed

II. Types of Viruses DNA viruses contain DNA nucleic acidDNA viruses contain DNA nucleic acid More stable and less prone to mutationMore stable and less prone to mutation Respond well to vaccinationRespond well to vaccination Ex: smallpox, chicken pox, herpes, HPV,Ex: smallpox, chicken pox, herpes, HPV, Hepatitis B Hepatitis B RNA viruses contain RNA nucleic acidRNA viruses contain RNA nucleic acid Prone to mutationsProne to mutations Require frequent vaccinationRequire frequent vaccination Ex: Influenza, H1N1, Hepatitis C, HIV,Ex: Influenza, H1N1, Hepatitis C, HIV, Rabies, Rotavirus, Yellow Fever Rabies, Rotavirus, Yellow Fever

Examples of Viral Disease Smallpox, the common cold, chickenpox, influenza, shingles, herpes, polio, rabies, ebola, hanta fever, and AIDSSmallpox, the common cold, chickenpox, influenza, shingles, herpes, polio, rabies, ebola, hanta fever, and AIDS

Different Hosts Host cell is very specificHost cell is very specific Animal hosts: rabies, HIV, chicken poxAnimal hosts: rabies, HIV, chicken pox Plant hosts: tobacco mosaic virus, carnation vein mottle potyvirusPlant hosts: tobacco mosaic virus, carnation vein mottle potyvirus C. Viruses that infect bacteria are called bacteria are called bacteriophages bacteriophages

1) Virus injects nucleic acid into cell, taking over its metabolism 2) Virus proteins and nucleic acids assemble into complete viruses 3) Virus enzyme breaks cell membrane and wall, releasing new viruses that attack other cells III. Lytic 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 ever time it divides. ever time it divides. Lysogenic Cycle

The viral DNA embedded in the host ’ s DNA is called a prophage.

V. Retroviruses A.Retroviruses contain RNA. Make a DNA copy FROM their RNA. Make a DNA copy FROM their RNA. Then this DNA is inserted into the DNA of the host Then this DNA is inserted into the DNA of the host cell. cell.

B. HIV (human immunodefiniciency virus) can lead to C. AIDS (acquired immunodefiniciency syndrome)

VI. Defense A.Vaccination offers protection for uninfected individuals individuals –Work by stimulating production of antibody forms memory cells without causing disease

Vaccines are made from killed or Vaccines are made from killed or weakened strains that cause antibody weakened strains that cause antibody production but not the disease production but not the disease

B. What are antibodies? Proteins that recognize invaders and block their effects Flags invaders for death by white blood cells

They depend on living thingsThey depend on living things Most likely developed after living cellsMost likely developed after living cells Are Viruses Living or Non-living? First viruses may have evolved from First viruses may have evolved from genetic material of living cells genetic material of living cells Cannot reproduce on their own Cannot reproduce on their own