It’s a Small Small WorldIt’s a Small Small World

Part A-Part A-VirusesViruses, Bacteria and , Bacteria and ProtistsProtists

VirusesViruses Viruses are nonliving particles Viruses are nonliving particles Biologists consider viruses Biologists consider viruses

nonliving because they do not nonliving because they do not exhibit all the criteria for lifeexhibit all the criteria for life

Made of a) Nucleic Acids Made of a) Nucleic Acids enclosed in a b) Protein Coatenclosed in a b) Protein Coat

Are smaller than the smallest Are smaller than the smallest bacteriumbacterium

Viruses require a host cell to Viruses require a host cell to reproduce or replicatereproduce or replicate

Viruses are named for the Viruses are named for the disease they cause ex: Polio, disease they cause ex: Polio, InfluenzaInfluenza

A virus that infects a A virus that infects a bacterium is called a bacterium is called a bacteriophagebacteriophage

Virus ReplicationVirus Replication 1. Virus locks onto a receptor 1. Virus locks onto a receptor

site on the host cell site on the host cell membrane, viruses are membrane, viruses are species specificspecies specific Exception to the rule is flu, can Exception to the rule is flu, can

infect animals and humansinfect animals and humans 2. The virus injects its nucleic 2. The virus injects its nucleic

acid into the host cell and the acid into the host cell and the host cell makes the viral DNA host cell makes the viral DNA with it’s own-with it’s own-LysogenicLysogenic CycleCycle

The Lysogenic phase can The Lysogenic phase can continue for many yearscontinue for many years

New viruses are released New viruses are released from the host cell killing it from the host cell killing it and go on to infect other host and go on to infect other host cells-cells-LyticLytic cyclecycle

Retroviruses-HIVRetroviruses-HIV HIV or Human Immuno HIV or Human Immuno

Deficiency Virus are RNA Deficiency Virus are RNA virusesviruses

Once inside the host’s cell Once inside the host’s cell the virus makes DNA from the virus makes DNA from its RNAits RNA

Uses Reverse Transcriptase Uses Reverse Transcriptase enzyme to make double enzyme to make double stranded DNA from viral stranded DNA from viral RNARNA

HIV infects white blood cellsHIV infects white blood cells Newly made viruses are Newly made viruses are

released into the blood released into the blood stream by exocytosisstream by exocytosis

People gradually lose white People gradually lose white blood cells because viruses blood cells because viruses in the lytic cycle kill the in the lytic cycle kill the host cellshost cells

http://http://www.metacafe.cowww.metacafe.com/watch/m/watch/2673927/2673927/hiv_replication_life_hiv_replication_life_cycle_3d_medical_cycle_3d_medical_animation/animation/

Cancer and VirusesCancer and Viruses Some viruses like the Some viruses like the

Hepatitis B virus has been Hepatitis B virus has been linked to cancer of the liverlinked to cancer of the liver

HPV or Human Papilloma HPV or Human Papilloma virus has been linked to virus has been linked to uterine canceruterine cancer

The first virus to be The first virus to be identified was a plant virus identified was a plant virus called tobacco mosaic virus. called tobacco mosaic virus. There are more than 400 There are more than 400 viruses that affect plants.viruses that affect plants.

Plant viruses require insects Plant viruses require insects or wounds to enter the hostor wounds to enter the host

Prions and ViroidsPrions and Viroids Two other important particles that Two other important particles that

behave like viruses and cause disease behave like viruses and cause disease areare

1. 1. PrionsPrions-Proteins that have no nucleic -Proteins that have no nucleic acid to carry genetic information. acid to carry genetic information. Cause other proteins to fold Cause other proteins to fold incorrectly.incorrectly.

2. 2. ViroidsViroids-single circular strands of -single circular strands of RNA with no protein coat. Cause RNA with no protein coat. Cause disease in plants.disease in plants.

QuestionsQuestions 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 Does a virus satisfy all of the criteria for a living

organism?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 What is the difference between the Lysogenic and Lytic

viral stages?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?