It’s a Small Small World Part A-Viruses, Bacteria and Protists

Viruses Viruses are nonliving particles Viruses are nonliving particles Biologists consider viruses nonliving because they do not exhibit all the criteria for life Biologists consider viruses nonliving because they do not exhibit all the criteria for life Made of a) Nucleic Acids enclosed in a b) Protein Coat Made of a) Nucleic Acids enclosed in a b) Protein Coat Are smaller than the smallest bacterium Are smaller than the smallest bacterium Viruses require a host cell to reproduce or replicate Viruses require a host cell to reproduce or replicate Viruses are named for the disease they cause ex: Polio, Influenza Viruses are named for the disease they cause ex: Polio, Influenza A virus that infects a bacterium is called a bacteriophage A virus that infects a bacterium is called a bacteriophage

Virus Replication 1. Virus locks onto a receptor site on the host cell membrane, viruses are species specific 1. Virus locks onto a receptor site on the host cell membrane, viruses are species specific Exception to the rule is flu, can infect animals and humans Exception to the rule is flu, can infect animals and humans 2. The virus injects its nucleic acid into the host cell and the host cell makes the viral DNA with it’s own-Lysogenic Cycle 2. The virus injects its nucleic acid into the host cell and the host cell makes the viral DNA with it’s own-Lysogenic Cycle The Lysogenic phase can continue for many years The Lysogenic phase can continue for many years New viruses are released from the host cell killing it and go on to infect other host cells-Lytic cycle New viruses are released from the host cell killing it and go on to infect other host cells-Lytic cycle

Retroviruses-HIV HIV or Human Immuno Deficiency Virus are RNA viruses HIV or Human Immuno Deficiency Virus are RNA viruses Once inside the host’s cell the virus makes DNA from its RNA Once inside the host’s cell the virus makes DNA from its RNA Uses Reverse Transcriptase enzyme to make double stranded DNA from viral RNA Uses Reverse Transcriptase enzyme to make double stranded DNA from viral RNA HIV infects white blood cells HIV infects white blood cells Newly made viruses are released into the blood stream by exocytosis Newly made viruses are released into the blood stream by exocytosis People gradually lose white blood cells because viruses in the lytic cycle kill the host cells People gradually lose white blood cells because viruses in the lytic cycle kill the host cells com/watch/ / hiv_replication_life_cy cle_3d_medical_anim ation/ com/watch/ / hiv_replication_life_cy cle_3d_medical_anim ation/

Cancer and Viruses Some viruses like the Hepatitis B virus has been linked to cancer of the liver Some viruses like the Hepatitis B virus has been linked to cancer of the liver HPV or Human Papilloma virus has been linked to uterine cancer HPV or Human Papilloma virus has been linked to uterine cancer The first virus to be identified was a plant virus called tobacco mosaic virus. There are more than 400 viruses that affect plants. The first virus to be identified was a plant virus called tobacco mosaic virus. There are more than 400 viruses that affect plants. Plant viruses require insects or wounds to enter the host Plant viruses require insects or wounds to enter the host

Prions and Viroids Two other important particles that behave like viruses and cause disease are Two other important particles that behave like viruses and cause disease are 1. Prions-Proteins that have no nucleic acid to carry genetic information. Cause other proteins to fold incorrectly. 1. Prions-Proteins that have no nucleic acid to carry genetic information. Cause other proteins to fold incorrectly. 2. Viroids-single circular strands of RNA with no protein coat. Cause disease in plants. 2. Viroids-single circular strands of RNA with no protein coat. Cause disease in plants.

Questions What is a virus? What is a virus? Is a virus smaller or larger than a bacteria? Is a virus smaller or larger than a bacteria? Is a virus living or nonliving? Is a virus living or nonliving? Does a virus satisfy all of the criteria for a living organism? Does a virus satisfy all of the criteria for a living organism? Describe the structure of a virus? Describe the structure of a virus? Why does a virus require a host? Why does a virus require a host? Explain how a virus replicates. Explain how a virus replicates. What is the difference between the Lysogenic and Lytic viral stages? What is the difference between the Lysogenic and Lytic viral stages? What enzyme does HIV use to replicate in the host cell? What enzyme does HIV use to replicate in the host cell? Name two cancers that are caused by viruses. Name two cancers that are caused by viruses. What is a prion and a viroid? What is a prion and a viroid?