Viruses Living or Not ???????

Viruses Virus – Latin for “_Poison__” Virus – Latin for “_Poison__” Russian Biologist Dmitri Ivanovski (1892) – Tobacco Mosaic Disease…not determined to be a virus until 1930…known as the first virus to be discovered!~ Russian Biologist Dmitri Ivanovski (1892) – Tobacco Mosaic Disease…not determined to be a virus until 1930…known as the first virus to be discovered!~

Characteristics of Viruses Scientist that studies viruses is called a virologist! Among the smallest biological particles (not cells) that are capable of causing harm in living organisms. Among the smallest biological particles (not cells) that are capable of causing harm in living organisms. Virus particles are called virions Virus particles are called virions 5000 influenza viruses can fit inside the head of a pin! 5000 influenza viruses can fit inside the head of a pin!

Studying the “T4-Bacteriophage Also known as: “eaters of bacteria” have a head and tail region – (serve as the principle experimental object in studying viruses) Also known as: “eaters of bacteria” have a head and tail region – (serve as the principle experimental object in studying viruses) Why study it?

VIRUSES & CELLS CharacteristicVIRUSCELL Structure DNA or RNA core, capsid Reproduction Only within a host Genetic Code DNA or RNA Growth/DvpmtNO EnergyNO Response to Environment No Change over time Yes

Not Considered Living A virus is not a bacteria, fungus, protist, plant or animal. A virus is not a bacteria, fungus, protist, plant or animal. They do not carry out cellular functions. They do not carry out cellular functions. They do not grow or undergo division They do not grow or undergo division A virus can not replicate on their own – they need to infect a HOST and use the hosts organelles and enzymes to do this! A virus can not replicate on their own – they need to infect a HOST and use the hosts organelles and enzymes to do this!

Viruses - Disease Viral infections generally behave in 2 ways: 1. Viruses reproduce and cause disease immediately (lytic or active) 2. Viruses integrate into the host cell (lysogenic or dormant)

Viral Replication – Lytic Cycle Infection See clip on desktop!!

LYSOGENIC CYCLE See clip on desktop!!!

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What Organisms and Host Cells Do Viruses Infect? Infection by viruses Infection by viruses viruses infect bacteria, plants, animals and other living organisms in order to reproduce viruses infect bacteria, plants, animals and other living organisms in order to reproduce a given virus usually infects a limited number of species. a given virus usually infects a limited number of species. within a host organism, usually only a limited number of cell types are susceptible to infection by a given virus within a host organism, usually only a limited number of cell types are susceptible to infection by a given virus Host range Host range array of host cells that a particular virus can infect array of host cells that a particular virus can infect determined by a “lock-and-key” fit between the virus and a receptor on the surface of a host cell determined by a “lock-and-key” fit between the virus and a receptor on the surface of a host cell Ex: one type of herpes virus causes cold sore, a different one causes genital sores! Ex: one type of herpes virus causes cold sore, a different one causes genital sores!

Virus Structure Nucleic acid Envelope Capsid

How are Viruses Classified? Genetic Material Genetic Material DNA or DNA or RNA (retrovirus/mutates frequently) RNA (retrovirus/mutates frequently) But not both But not both Capsid (Protein) Structure (95% of virus) Capsid (Protein) Structure (95% of virus)  Helical (rod shaped)  Polyhedral (spherical)  Complex Presence or absence of a membranous envelope surrounding the capsid Presence or absence of a membranous envelope surrounding the capsid **No envelope = naked virus Helical Marburg virus Polyhedral SV40 virus Complex bacteriophage

HIV, for example, only will enter cells that have a surface protein molecule called CD4. These molecules are found only on white blood cells. Thus, HIV will only infect white blood cells and not lung cells or other cell types. Sometimes, a virus can mutate and change its host range. This appears to be happening with the avian flu virus (influenza A/H5N1) currently circulating. At first, the flu virus could infect only birds, but changes in the virus genome have allowed it to infect humans. So now, its host range has expanded. The change in host range of a virus can be one factor in the emergence of a new disease. Host Range

What Diseases are Caused by Viruses? Infectious diseases Infectious diseases RNA viruses (retroviruses)DNA viruses AIDSRespiratory Disease Influenza (flu) Smallpox Common coldChickenpox PolioMononucleosis MeaslesCold Sores Tumor Viruses – cause Cancer ex: HPV Tumor Viruses – cause Cancer ex: HPV

How Can Viral Diseases Be Prevented and Treated? Good hygiene Good hygiene Avoid contact with contaminated food, water, fecal material or body fluids. Avoid contact with contaminated food, water, fecal material or body fluids. Wash hands frequently. Wash hands frequently. Vaccines Vaccines Stimulate natural defenses with in the body. Stimulate natural defenses with in the body. Contain a component of or a weakened or killed virus particles. Contain a component of or a weakened or killed virus particles. Are developed for many once common illnesses such as smallpox, polio, mumps, chicken pox. Are developed for many once common illnesses such as smallpox, polio, mumps, chicken pox. Not available for all viruses. Not available for all viruses. Anti-viral drugs (but not antibiotics) Anti-viral drugs (but not antibiotics) Available for only a few viruses. Available for only a few viruses. Inhibit some virus development and/or relieve symptoms. Inhibit some virus development and/or relieve symptoms.

How Do New Viruses Emerge? Through mutation and evolution of genetic code…changes to the protein coat therefore changing the “lock and key” fit! And no longer recognizable to a host’s immune system! Through mutation and evolution of genetic code…changes to the protein coat therefore changing the “lock and key” fit! And no longer recognizable to a host’s immune system! Human population expanding into previously uninhabited areas (increased contact between humans and animals) Human population expanding into previously uninhabited areas (increased contact between humans and animals) Through the detection of previously unrecognized viruses Through the detection of previously unrecognized viruses

HSV1 vs HSV2

Human Papilloma Virus – 14yo boy

Polio Virus Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating

VIRUS MINI QUIZ 1. THE PRIMARY FUNCTION OF ALL VIRUSES IS TO REPLICATE!!

MINI QUIZ… 2. WHAT IS THE TYPICAL/COMMON VIRUS THAT STUDENTS STUDY WHEN LEARNING ABOUT VIRUSES? T4 Bacteriophage

MINI QUIZ… 3. IN ORDER FOR A VIRUS TO REPLICATE IT NEEDS TO BE IN A HOST CELL

MINI QUIZ… 4. VIRAL REPRODUCTION THAT KILLS THE HOST CELL IS CALLED THE Lytic CYCLE!

MINI QUIZ… 5. WHEN VIRAL DNA IS EMBEDDED INTO A HOST CELL’S DNA IT FORMS A PROPHAGE

MINI QUIZ… 6. ANOTHER NAME FOR INFLUENZA IS FLU VIRUS

MINI QUIZ… 7. 3 WAYS VIRUSES CAN BE TREATED/PREVENTED ARE…. 1. Hygiene 2. Vaccines 3. AntiVirals

MINI QUIZ… 8. SCIENTISTS THAT STUDY VIRUSES ARE CALLED VIROLOGISTS

MINI QUIZ… 9. 3 WAYS THAT VIRUSES CAN BE TRANSMITTED ARE…. -- droplets in the air (e.g. cold, flu, tuberculosis) -- via food or water (e.g. Salmonella, food poisoning) -- via mosquitoes, ticks (e.g. malaria, West Nile virus, Lyme disease) -- physical contact (e.g. pinkeye, herpes, chickenpox, sexually transmitted diseases)

MINI QUIZ… 10. A VIRUS THAT HAS ONLY A CAPSID SURROUNDING IT’S GENETIC INFORMATION AND NO ENVELOPE IS CALLED A NAKED VIRUS.