VIRUSES

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

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

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

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, Hepatitis C, HIV, Rabies,Ex: Influenza, Hepatitis C, HIV, Rabies, Rotavirus, Yellow Fever 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 Viruses that infect bacteria are called 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 can attack other cells

1. A host cell makes copies of the virus indefinitely indefinitely 2. Virus integrates its DNA into the DNA of the host cell the host cell 3. Viral genetic information replicates along with the host cell’s DNA. along with the host cell’s DNA. Lysogenic Cycle

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

Retroviruses Retroviruses contain RNA.Retroviruses contain RNA. When retroviruses infect cells, they make a DNA copy of their RNA.When retroviruses infect cells, they make a DNA copy of their RNA. This DNA is inserted into the DNA of the host cell.This DNA is inserted into the DNA of the host cell.

HIV (Human Immunodeficiency Virus) can lead to AIDS (Acquired Immunodeficiency Syndrome)

Defense Vaccination offers protection for uninfected individualsVaccination offers protection for uninfected individuals Work by stimulating production of antibody forms memory cells without causing diseaseWork 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

What are 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

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