Ch 13 – Microbiology – Flashcards
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| virus characteristics |
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| -small infectious agents -can infect most living things -bacteriophages attack bacteria -reproduce at high rate (require host) -can mutate -acellular (no cytoplasm or organelles) -no metabolism of their own -replicate using hosts machinery -possess DNA or RNA never both |
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| Ivanowski |
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| -in 1892 shows that the tobacco mosaic disease is caused by an agent that passes through a porcelain filter |
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| viral genome |
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| -Single or segmented, circular or linear molecule of nucleic acid functioning as the genetic material of the virus -Can be single-stranded or double-stranded DNA or RNA (but never both) -Codes for the synthesis of viral components and viral enzymes for replication |
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| capsid |
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| -Protein shell surrounding the genome -Usually composed of protein subunits called capsomeres -Protect and introduce the genome into host cells. |
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| viral envelope |
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| -Composed of phospholipids and glycoprotein -Derived from host cell membranes by a process called budding -Depending on the virus, envelopes may be covered by spikes made of carbohydrates-protein complexes that helps the virus to attach to the host cell |
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| enveloped viruses |
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| -Nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope (herpes) |
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| binal (complex) virus |
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| Pleomorphic (irregular shape), or have complex structures |
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| virus size range |
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| 5-300nm |
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| helical viruses |
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| nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure (tobacco mosaic) |
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| Polyhedral viruses |
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| nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the form of an icosahedron (Mastadenovirus) |
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| classification of viruses |
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| -type of nucleic acid -shape of capsid -enveloped or naked |
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| viruses with ds DNA(+/-) |
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| -the (-) DNA is directly transcribed into viral mRNA -bacteriophages, papovaviruses, adenoviruses, herpesviruses |
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| viruses with (+) DNA or (-) DNA |
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| -once inside the host, it is converted into ds DNA and the (-) strand is transcribed into viral mRNA -Phage M13, Parvoviruses |
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| viruses with (+) RNA |
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| -a (+) RNA is copied into (-) RNA that is transcribed into viral mRNA -Picorna viruses, Togaviruses, Corona viruses |
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| viruses with (-) RNA |
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| -the (-) RNA is copied into (+) RNA which functions as viral mRNA -Orthomysoviruses, Paramysoviruses, Rhabdoviruses |
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| viruses with ds RNA (+/-) |
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| -the (+) RNA functions as viral mRNA -Reoviruses |
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| viruses with (+) RNA |
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| -the (+) RNA is reverse transcribed into (-)DNA that makes a complementary copy to become (+/-) DNA -the DNA is transcribed to make viral mRNA -Retroviruses |
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| viral replication of bacteriophages |
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| -lysogenic and lytic cycle |
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| steps of lytic cycle |
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| -attachment -penetration -biosynthesis -maturation -release |
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| attachment (lytic cycle) |
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| -by chance, no energy required -involves attachment site on virus and receptor site on bacteria |
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| penetration (lytic cycle) |
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| -phage lysozyme is released and breaks down a portion of the cell wall -phage injects DNA |
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| biosynthesis (lytic cycle) |
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| -synthesis of viral nucleic acids and proteins in cytoplasm -host DNA is degraded -viral proteins interfere with transcription and it ceases -translation is repressed -early phase-many copies of the phage DNA are synthesized using the host's nucleotides and enzymes -late phase-host's ribosomes, enzymes, and amino acids are used for translation of viral proteins -during this eclipse period, the virus is not infectious |
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| maturation (lytic cycle) |
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| -assembly of capsid around genome -complete virions are produced |
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| release (lytic cycle) |
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| -plasma membrane lyses to to action of phage lysozyme -virions released to infect other bacteria |
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| lysogenic cycle |
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| -does not necessarily end with host cell death -these phages are able to incorporate their DNA into the host cell DNA -virus remains latent(inactive) |
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| lysogeny leads to...(3) |
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| -lysogenic cells are immune to re-infection of the same phage -phage conversion (cell exhibits new properties) -specialized transduction |
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| example of phage conversion |
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| -Corynebacterium diphteriae -diphteriae caused by toxin -gene encoding toxin is carried by a phage -so it only produces toxin when it carries the lysogenic phage -similar with Clostridrium botulinum |
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| Animal virus infection steps (6) |
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| -attachment -penetration -uncoating -biosynthesis -maturation -release and reinfection |
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| attachment (animal virus) |
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| -binding of attachment sites on viral surface with receptor sites on host cell membrane |
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| penetration (animal virus) |
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| -fusion with the host membrane -endocytosis |
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| uncoating (animal virus) |
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| -capsid is digested -release of viral genome |
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| biosynthesis (animal virus) |
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| -viral genome directs the host cell's metabolic to synthesize viral enzymes and viral parts -early phage- viral genome replicates thousands of times -late phase-viral structural proteins and enzymes involved in maturation are produced -during uncoating and replication, virus is not infectious |
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| viral structure proteins |
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| -capsid and matrix proteins -envelope glycoproteins |
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| maturation (animal phase) |
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| assembly of capsid around genome |
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| release and reinfection (animal virus) |
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| -virus obtains envelope by budding |
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| number of viruses that can be made from one host cell |
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| 10k to 50k |
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| viral latency |
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| -some ds DNA viruses like herpes virus and retrovirus are able to remain latent for long periods of time without replicating or causing harm -some remain latent in cytoplasm -others are able to integrate their DNA into host cell chromosomes(provirus) -results from the lack of production of specific host cell proteins that are required for activation of viral genes -activation of host cellls DNA in response to extracellular stimuli can lead to synthesis of specific host cell proteins required by virus -these proteins now activate viral genes leading to burst of replication via the productive life cycle |
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| examples of latent viruses |
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| -herpes simplex virus (HSV) (oral, genital) -Epstein-Barr virus (EBV)-replicate in epithelial cells, latent in B lymphocytes, mononucleosis |
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| persistent (chronic) viral infections |
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| -occur gradually over a long period rather than appearing suddenly -cervial cancer (HPV), AIDS-HIV-1, liver cancer HBV |
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| Herpesviruses |
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| -large genome 120kb, linear, ds -among most widespread of all infections -can establish latent infections which can reactivate years later producing acute infections -100 herpesviruses identified from oysters to humans -8 infect humans |
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| more on herpes |
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| -disease is initiated by direct contact (oral genital brain) -cause cytopathologic effects (degenerative changes in cells) -avoids antibodes by cell to cell spread -establishes latency in neurons (hides from immune system) -activated from latency by heat, cold, UV, stress, or immune suppression |
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| Herpes Simplex Virus (HSV) |
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| -common human pathogen -cause painful by benign lesions and recurrent disease -both type 1 and type 2 cause cause significant mortality when infecting eye or brain, in immunosupressed person, or newborn |
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| Varicella Zoster virus (VZV) |
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| -causes chicken pox (varicella) -when reactivated causes herpes zoster or shingles (rash along entire skin) -establish latent infections of neurons -characteristic blister-like lesions -spread predominantly by respiratory route -smallest genome of herpesvirus |
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| Hepatitis A virus (Acute Viral Hepatitis A) |
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| -common in US -30% of population show evidence of past infection due to anti-HAV antibodies -most infections are asympotomatic-confers lifelong immunity -long incubation period (15-50 days) before symptoms |
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| more on HAV |
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| -during incubation period, virus replicates in intestinal cells and shed in high concentrations in stools -transmitted via fecal-oral route (water, food, dirty hands) -outbreaks usually originate from common source (water supplies, restaurant, daycare) |
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| Hepatitis B Virus (HBV) |
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| -one of the most frequently reported vaccine preventable diseases in US -HBV causes acute and chronic hepatitis -spread though sexual contact, blood transfusion, exposure to blood via open cuts, opens spores, needle/razor sharing, ear piercing |
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| more on HBV |
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| -can be spread from mother to child from birth -incubation period 4-25 weeks -90% are considered acute -10% chronic may progress to cirrhosis, liver failure or liver cancer |
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| HIV/AIDS |
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| -33 people worldwide living with HIV/AIDS -14 million AIDS deaths since beginning of epidemic -close to 1 million US AIDS cases -caused by HIV-1 or HIV-2 |
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| HIV structure |
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| -enveloped RNA -2 copies of (+) RNA genome -9 viral genes -encodes viral proteins (gp41, gp120) that mediate infection of target cells |
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| human cells possessing CD4 |
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| -T4 helper lymphocytes -monocytes -macrophages -dendritic cells |
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| HIV disease mechanism |
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| -results in progressive immune deterioration due to decreased number and function of CD4+ T lymphocytes (helper T-cells) -initial infection of dendritic cells or other macrophages in epithelium -moves to lymphoid regions where replication reaches critical levels -macrophages are persistently infected creating a major reservoir and means of distribution |
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| more on HIV disease mechanism |
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| -CD8 T cells can kill infected cells but CD8 T cells require activation of CD4 T cells -as CD4 decreases, CD8 decreases -reduction of CD8 correlates to disease progression to AIDS |
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| Human papillomavirus |
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| -very common infection -20 million people infected -at least 50% of sexually active people acquire genital HPV at some pt in their lives -by age 50, 80% of women will have acquired genital HPV infection -6.2 million get a new genital HPV each year |
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| more on HPV |
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| -more than 100 different types -some cause benign skin warts or papillomas -common warts are spread environmentally or skin to skin contact -seperate group of 30 HPVs are through sexual contact |
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| High Risk HPVs |
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| -about a dozen can cause cancers (most mostly cervical cancer) -HPV induced cancers often have viral sequences integrated into the cellular DNA -some of the HPV "early" genes (E6 and E7) are known to act as oncogenes that tumor growth and malignant transformation |
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| oncogene |
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| -modified gene or set of nucleotides that code for a protein that increases the malignancy of a tumor cell -some usually involved in early stages of cancer increase chance that a normal cell develops into a tumor cell possibly resulting in cancer |
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| growing viruses (4) |
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| -growing virus in living animals -growing virus in embryonic egg -growing virus in cell culture -growing bacteriophages |
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| growing viruses in living animals |
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| -used to be the only way -not extensively used anymore except for growth of viruses that develop in an animal -ex. Coxsackievirus A-painful blisters in mouth, thoat, hands, feet, conjunctivitis (eyelid swelling) |
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| growing virus in embryonic egg |
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| -viral growth is indicated by damage/death of embryo or lesions on egg membrane |
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| growing virus in cell culture |
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| -a tissue is treated with enzymes to separate the cells -cells are suspended in culture medium -normal cells or primary cells grow in a monolayer across glass or plastic container. Transformed or continuous cells do not grow in the monoculture |
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| growing bacteriophages (plaque method) |
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| -a sample of bacteriophage is mixed with host bacteria and melted agar -mixture is poured into a petri plate containing a layer of agar growth medium -each virus infects a bacterium, multiply, and release hundreds of new viruses that will infect other bacteria -destruction of bacteria produces a clearing or a plaqueviro |
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| viroids |
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| -small circular single stranded molecules of infectious RNA lacking a protein coat -cause of few plant diseases -viroid RNA does not code for any protein -usually transmitted by seed or pollen -infected plants can show distorted growth -ex. Potato spindle tuber disease-all tomatoes and potatoes are susceptible and there is no natural resistance |
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| Hepatitis D |
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| -only known disease to be caused by viroid -delta agent is a viroid enclosed in a Hep B virus capsid -there is extensive sequence complementarity between Hep D viroid RNA and human liver cell 7S RNA, a small cytoplasmic RNA -causes liver death by sequestering 7S RNA of cleaving it -can only enter human cell if enclosed in a capsid that contains a binding protein (it obtains this from Hep B virus) -the delta agent that enters blood can be transmitted via blood or serum transfusions |
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| prions |
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| -small proteinaceous particles -controversy if it contains nucelic acid (if so, it has very little, not enough to code for protein) -infect and propagate by refolding into a structure which is able to convert normal protein into abnormally structured protein -cause neurodegenerative disease by aggregating in CNS to form plaques called amyloids which disrupt normal tissue structure -this disruption is characterized by holes with spongy architecture due to loss of neurons |
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| isoforms |
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| -the proteins that prions are made of -found throughout body -prion protein found in infectious material has a different structure and is resistant to proteases |
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| PrP^c |
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| -normal protein found on membrane of cells |
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| Prp^Sc |
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| -infectious isoform of Prp^c -able to catalyze formation of other normal proteins into infectious ones by changing conformation |
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| Prp^Sc mechanism of infection |
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| -prp is produced by cells -prpSc acquired or produced by altered gene -prpSc reacts with prp on cell surface and converts it to prpSc -new prpSc converts more prp -prpSc is takin in cell by endocytosis -prpSc accululates in endosomes -prpSc continues to accumulate as it is transfered to lysozomes -results in cell death |
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| Bovine spongiform encephalopathy (mad cow disease) |
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| -fatal neurodegenerative disease -transmissions occurs when healthy animals come in contact with infected tissues -was widespread in Europe in 1987 due to meat and bone meal and animal cadavers used as cattle feed -can be transferred to human beings who eat or inhale material from infected carcasses (Creutzfeldt-Jakob disease)(nvCJD or vCJD) -first symptoms of CJD is rapidly progressive dementia, memory loss, personality changes, hallucinations, speech impairment, jerky movements, balance and coordination dysfunction (ataxia), rigid posture, seizures |
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| Kuru |
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| -laughing sickness -first noted in New Guinea in 1900s -by 1950s anthropologists reported that kuru (trembling with fear) was rampant throughout South Fore -due to ritual acts of mortuary cannibalism |
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| symptoms of kuru first stage |
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| -ambulant stage-unsteadiness of stance, voice, hands, eyes, deterioration of speech, tremor, shivering, loss of coordination in lower extremities that moves slightly upwards, slurring speech |
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| symptoms of kuru second stage |
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| -sedentary stage -no longer walk without support, more severe tremors and ataxia, shock-like muscle jerks, outbursts of laughter, depression, mental slowing |
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| kuru symptoms 3rd stage |
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| -terminal stage -inability too sit up without support, severe ataxia, tremor and slurring of speech, urinary and fecal incontinence, difficulty swallowing, deep ulcerations |
