Viruses Viruses are not classified in any kingdom. They show no traits like the living things in the 6 kingdoms we will be studying. WHAT IS A VIRUS?

vs A. General Characteristics 1. A virus (aka virion) is an infectious agent made up of – nucleic acid (DNA or RNA), wrapped in protein coat a. they have no nucleus, no organelles, no cytoplasm or cell membrane – non-cellular particle b. viruses have either – DNA or RNA, but not both vs

Ex: HIV, flu (influenza), cold c. viruses with RNA that transcribes into DNA (using enzyme reverse transcriptase) are called – retroviruses Ex: HIV, flu (influenza), cold RNA viruses have a high rate of mutations – replication of RNA does not involve proofreading step (as in DNA replication) HIV Infected Cell (This is the reason why HIV is so incurable.)

2. Viruses are - parasitic - organism that depends 2. Viruses are - parasitic - organism that depends entirely upon another living organism (host) for its existence in such way that it harms that organism. A flea is a parasite to a dog and is harmful to the dog.

1. Bacteriophage—viruses that infect a bacteria B. Examples 1. Bacteriophage—viruses that infect a bacteria Capsid (protein coat) 2. Flu (influenza), HIV DNA Tail fibers Envelope—has marker proteins + carbs derived from host cell RNA Capsid

Bacteriophage—a virus that infects bacteria (bacteria is the host) Capsid Nucleic Acid Bacteriophage—a virus that infects bacteria (bacteria is the host)

C. Replication (reproduction): How a virus spreads. ***A virus CANNOT reproduce by itself—it must invade a host cell and take over its activities. 1. Virus (bacteriophage) invading a bacterium (E. coli) Virus uses what it needs from cell + makes more virus Lytic = split Virus attaches to cell DNA of virus enters cell Cell bursts, new viruses are released Cell divides, replicating DNA of virus Virus DNA becomes part of cell’s DNA

2. During Lysogenic Cycle, it is possible for viral DNA to separate 2. During Lysogenic Cycle, it is possible for viral DNA to separate from host cell DNA and cause cell to enter Lytic Cycle and replicate new viruses Virus uses what it needs from cell + makes more virus Lytic = split Virus attaches to cell DNA of virus enters cell Cell bursts, new viruses are released Cell divides, replicating DNA of virus Virus DNA becomes part of cell’s DNA

Lytic Cycle of a Bacteriophage rapid replication of the virus, ending in cell lysis (or death). More phages are released to infect other cells

Lysogenic Cycle of a Temperate Bacteriophage the virus stays within the cell until certain environmental triggers cause it to enter the lytic cycle

Warm-Up Get out a spare sheet of paper. YOU MAY NOT USE NOTES!!!!! What is a Bacteriophage? Why are Retroviruses so hard to kill? What is an example of a Retrovirus? Describe the Lytic and Lysogenic Cycles.

Virus DNA becomes part of cell’s DNA 3. Virus invading an animal cell: Ex: HIV invading human cell Virus DNA becomes part of cell’s DNA Envelope of HIV contains marker proteins + carbs derived from host cell Virus particle enters human cell by endocytosis New virus buds off RNA replicates

Ex: the rabies virus only infects brain or nervous cells 4. Capsid proteins of a virus bind to receptors on cell surface and “trick” cell into allowing it inside. Because of this fit between virus and cell receptors, most viruses are specific for cells they infect. Ex: the rabies virus only infects brain or nervous cells Receptor Sites Virus Cell

Human Immunodeficiency Virus

D. Importance: a. Causes disease—pathogenic 1. Harmful a. Causes disease—pathogenic Disease producing agent—pathogen b. Human Diseases: DNA: chicken pox, mono, cold sores, genital herpes, warts, hepatitis, smallpox RNA: cold, influenza, polio, AIDS, rabies, Ebola c. Viruses disrupt the body’s normal equilibrium/balance (homeostasis) d. Viruses can be prevented with vaccines, but NOT treated with antibiotics.

2. Beneficial a. genetic engineering – harmless virus carries good genes into cell

Gene Therapy

Virus Living Cell Genetic material (DNA or RNA) + capsid Cell membrane, cytoplasm, genetic material, organelles Structure Copies itself only inside host cell Cell division --Asexual or Sexual Reproduction DNA and RNA Genetic Material DNA or RNA Growth and Development NO YES Obtain and Use Energy NO YES Response to Environment YES NO Change over time YES YES

Are viruses living? NON - LIVING TWO How many characteristics of life do viruses possess? TWO *contains Genetic Material *change over time Are viruses living? NON - LIVING

Warm-up Describe the structures of the HIV virus to the right  2. Are all viruses bad? If not, explain a positive use for Viruses 3. After you are given a cell and surface marker find your match and go visit Ms. Lust for some “medicine”.