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UOP Microbiology
Lecture 19: Viruses, Viroids, Prions
| Question | Answer | ||
|---|---|---|---|
| tissue tropism | virus has an affinity towards a particular host | ||
| Epstein Barr Virus (EBV) | mononucleosis; specific for human B lymphocytes | ||
| Rabies virus | infects any type of nervous tissue in any warm-blooded animal | ||
| viral genomes | can be DNA or RNA (dsDNA, dsRNA, ssDNA, ssRNA); linear, circular, SMALL; nucleic acid core | ||
| capsid | can be helical, polyhedral, or complex (bacteriophage); characteristic # of capsomeres; surrounding protein coat that gives it shape and protection | ||
| envelope | lipid + protein membrane over capsid; w/o envelope, enveloped viruses cannot infect; plays role in host recognition because it is acquired from host cell | ||
| spikes | contain enzymes for attachment | ||
| viron | completely assembled, infectious virus | ||
| lytic replication cycle in bacteriophage | attachment, entry, biosynthesis, maturation, release | ||
| attachment | tail/viral capsid binds receptor onto host cell wall | ||
| entry | virus injects intracellularly, capsid extracellular | ||
| biosynthesis | viral proteins made, host nucleic acid degraded | ||
| maturation | viral assembly | ||
| release | host destroyed, new viruses released | ||
| burst size | # of phage made (50-200) | ||
| burst time | time from attachment --> release | ||
| How animal viruses enter cells | direct penetration, membrane fusion, endocytosis | ||
| direct penetration | capsid goes into host cell through cytoplasmic membrane (w/ receptors on surface) | ||
| membrane fusion | viral glycoproteins remain in cytoplasmic membrane and capsid uncoats | ||
| endocytosis | the host cell engulfs whole virus and capsid uncoats | ||
| (+)-stranded or sense RNA virus | genome acts as mRNA, used for template for translation of viral proteins; translate into polypeptides; Ex) Polio virus | ||
| (+)-stranded or sense RNA virus | genome acts as mRNA, used for template for translation of viral proteins; translate into polypeptides; Ex) Polio virus | ||
| dsRNA virus | (+)or sense RNA virus used as template for translation for viral protein; Ex) Rotovirus | ||
| Retrovirus | ssRNA undergoes reverse transcriptase creating ssRNA and ssDNA complementary strands; then RNA strand goes away due to the RNAse leading to ssDNA; the ssDNA turns into dsDNA with DNA polymerase | ||
| provirus | viral DNA integrates into host cell genome (lysogenic); immune to host cell Ab because they cannot penetrate cells | ||
| antibacterial drugs | not effective against viral infections because viruses use host enzymes and machinery and has no cell walls | ||
| antiviral drugs | most disrupt at critical stage of viral replication: 1)antagonize attachment, 2)inhibit viral uncoating, 3)inhibit viral nucleic acid synthesis, 4)reverse transcriptase inhibitors, 5)protease inhibitors, 6) viral protein inhibitors | ||
| Pleconaril | (1) blocks attachment molecules on host cell/pathogen | ||
| Tamiflu | (1) Neuraminidase inhibitors prevent influenza from attaching/ exiting cells | ||
| Amantadine | (2) Neutralizes the acidic environment within phaglosome that's necessary fro viral uncoating | ||
| Acyclovir | (3) genital herpes, chickenpox; Base analogs look like nucleosides and once incorporated, stop synthesis of nucleic acids | ||
| Azidothymidine (AZT) | (3) for HIV; Base analogs look like nucleosides and once incorporated, stop synthesis of nucleic acids | ||
| Nevirapine | (4) bind and inhibit reverse transcriptase; blocks replication of retroviruses | ||
| Saquinivir | (5) Looks like peptide bond that's normally attacked by protease, decoys; protease function required for HIV capsid construction | ||
| Fomiversen | (6) Specific against cytomegalovirus; directly inject into eye humor; binding prevents protein synthesis by blocking ribosomes (complementary to mRNA); antisense nucleic acids | ||
| Bovine Spongiform Encephalopathy | 8-12 year incubation; no nucleic acid (can withstand heat, radiation, nucleases); sensitive to phenol, urea, incineration, and autoclaving @1N NaOH | Jakob-Creutzfeld disease | Mad cow disease |
| Normal Prion Protein (PrPc) | binds copper in brain (copper required for superoxide dismutase which protect cells from oxygen-free radicals) | cellular PrP = "good prion" | more alpha-helical |
| superoxide dismutase | gathers superoxide dismutase radicals and prevent them from affecting DNA | ||
| Prion PrP (PrPsc) | Normal prion in wrong conformation; ingested misshapen prion may travel to brain and change normal prion proteins causing disease | "bad prion" | more Beta-sheath |
| Interferon | part of innate immunity; 20 proteins produced by body cells in response to viral invasion; stimulates production of antiviral proteins (AVPs) that interfere with viral reproduction in neighboring cells | ||
| Viroids | extremely small, circular pieces of RNA taht are infectious and pathogenic in plants; similar to RNA but lack capsids; Ex) PSTV |
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