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UIUC MCB 100 - Ch. 13: Viruses (cont.)

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MCB 100 1st Edition Lecture 39 Outline of Last Lecture I. Early animal shelteringII. Humane ShelteringIII. Animal sheltering across the countryIV. Pet Overpopulation film Outline of Current Lecture I. Human and animal viruses (cont.) II. Other types of viruses Current LectureI. Human and animal virusesa. Some human viruses are always in a lytic cycle- these viruses kill human cells i. Examples:1. Rhinoviruses: small RNA viruses that cause common cold 2. Enteroviruses: small RNA viruses that cause viral diarrhea3. Hepatitis A: RNA virus that attacks liver cells4. Hemorrhagic fever viruses- Yellow Fever and Ebola virus b. Some viruses may become latent (dormant) within human cells- these viruses have astage in their life cycle that includes a DNA copy of their genome- they may disrupt regulation of cell division and possibly cause canceri. Examples:1. Retroviruses: RNA viruses that replicate via DNA intermediates Human Immunodeficiency Virus (HIV)2. Some DNA viruses: Herpes viruses, Chickenpox, Hepatitis B b. Some animal viruses exit host cell by budding- unlike lysis, budding doesn't kill host cell- viral envelope is derived from the cytoplasmic membrane of the old host cell, with some viral proteins embedded within it- viral glycoproteins mark an infected cell with foreign antigens c. Some animal viruses exit host cell by lysis- these generally don’t have an envelope i. Example: Polio virus1. Classified in Picornaviridae family 2. Non-enveloped, + strand RNA virus3. Enterovirus (entero = intestines)4. Fecal- oral cycle pathogen5. Most causes show mild symptomsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.6. Even in very mild cases an infected host sheds virus particles7. Oral polio vaccine is a live, but attenuated/weakened virus8. Cause of polio disease:a. Death of infected cells a. Symptoms of primary infection are minor- diarrhea b. Neurological symptoms that include paralysis develop when virus is present in the body in high levels and secondary tissues are attackedc. Virus prefers to attack intestinal epithelial cells but may invade nerve cells as a secondary tissue tropismd. Death of nerve cells can lead to a loss of muscle coordination and paralysis. Only a small fraction of infections lead to paralytic disease2. Life cycle is similar to the T4 lytic cycle a. Host encounters pathogen: i. virus is ingested in contaminated water/food or otherwise enters the mouthb. Attachment to host cell: i. primary tissue tropism for polio is intestinal epithelial cellsii. virus coat proteins stick to receptors on surface of host cellb. Entry into host cell: i. host cell cytoplasmic membrane encircles the virus, enclosing it within a vesicleii. viral capsid breaks open depositing viral genomic RNA into cytoplasmb. Synthesis of viral components, mRNA, proteins, genomei. Viral genomic RNA is translated by host ribosomes, making viral proteinsii. Viral RNA-dependent RNA polymerase in cytoplasm copies virus RNAiii. Negative sense copy of the viral RNA is madeiv. The (-) sense strand of viral RNA is used as a template by the viral RNA polymerase to make new copies of the viral (+) strand RNAb. Assembly of new virus particlesi. Viral coat proteins spontaneously associated with viral (+) strand RNAb. Release from the old cell i. When the cell is full of virus particles it breaks openii. New virus particles infect other cells within the host or are excreted in feces II. Other types of virusesa. HIV (human immunodeficiency virus)i. Retrovirusii. Viral genomic material is (+) sense RNA but during replication, a double-stranded DNA copy of the genome is made by a viral enzyme called "reverse transcriptase" iii. HIV infections1. Prevalence vs. number of cases2. Prevalence: the rate of infection as a fraction of the population; commonly expressed in units of: cases/100,000 or in some instances, percentage3. Total number of cases in arbitrary geographical regions does not inform the reader of prevalenceii. Life cycle: 1. Attachment:a. HIV infects a type of white blood cell known as a T-helper cellb. Viral receptor is a protein called CD4c. CD4 is involved in cell-cell recognition of various types of immune system cellsd. T-helper cells assist in communication between various types of immune cellse. T-helper cells play a critical role in coordinating the immune response- death of T-helper cells shuts down host immunity!2. Entry:a. Virus envelope fuses with the host cell cytoplasmic membrane b. Envelope is a lipid bilayer that is derived from cytoplasmic membrane of old host cell2. Synthesisa. Viral RNA is read by the viral reverse transcriptase to make a ss DNA copyb. Viral ss DNA is converted to ds DNA by reverse transcriptasec. Viral DNA enters nucleus and is integrated into host chromosomed. Host RNA polymerase transcribes viral DNA sequences to make viral mRNAe. Viral proteins are made in the cytoplasm by host cell ribosomesf. Viral mRNA can act as viral genomic material2. Assemblya. Virion particle must contain viral reverse transcriptase enzymeb. Spontaneous assembly of capsidc. Spike proteins embedded in host cell membrane2. Releasea. New virus particles exit the cell by


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UIUC MCB 100 - Ch. 13: Viruses (cont.)

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