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MicroBio Exam 3
Viruses
| Question | Answer |
|---|---|
| What is a virus? | non-living, acellular microorganism, referred to as partical or virion |
| How do viruses replicate and reproduce? | They must invade a susceptible host cell and replicated by host cell replication process. |
| What affects do the process of cell invasion give? | pathogenic or cytopathic affects |
| What are the components of a virion? | Genetic material, protein coat or capsid, envelope or enzymes |
| What is another name for genetic material? | viral genome |
| What does genetic material consist of? | DNA (ds or ss) OR RNA (ds or ss) |
| Can genetic material consist of DNA and RNA? | never both |
| What are RNA genomes unique to? | viruses or viroids |
| How is the genetic material arranged? | Linear, circular or segmented |
| What kind of viruses have a protein coat? | ALL viruses |
| Protein coat is also known as? | capsid |
| What is a capsid comprised of? | capsomers |
| What are the functions of a capsomer? | 1. number and kind can aid in viral identification 2.determine shape 3. facilitate viral attachment to host cells |
| What is a capsid containing a genome and nothing else known as? | nucleocapsid |
| What kind of viruses contain an envelope? | Mostly animal viruses, but no bacterial viruses |
| What are the components of the envelope? | 1. bi-layer membrane 2. aquired by "budding" thru the cell membrane 3. Contain spikes 4. help evade host immune defenses |
| What do spikes do? | glycoproteins that help virus to attach to receptor sites on host cells |
| What are viruses without an envelope called? | naked viruses |
| Enzymes | only some virus particles contain these |
| What are the enzymes? | 1. lysozyme 2. RNA polymerase 3. Reverse transcriptase |
| Where are RNA polymerase enzymes found? | ds RNA viruses |
| Where are Reverse Transcriptase enzymes found? | ss RNA viruses |
| Viral replication : viral genome | instructions for disrupting or destroying host cell genome |
| Viral replication : replication | results in new viral genomes : acted on by host cell's systems |
| Viral replication : transcription and translation | uses destructive enzymes, creates viral capsids and enzymes |
| Host range and specificity | most viruses infect one host and specific cells or tissues within that host |
| Papilloma virus infects what cells? | human skin cells |
| Host range and specificity | select viruses affect multiple hosts or a variety of cell types in a host |
| What is a spectrum of hosts that a virus can infect? | host range |
| What animals does Rabies infect? | many different animal types |
| What are specific kinds of cell a virus can infect within a host cell? | viral specificity |
| What is the traditional 3 category system of virus classification? | 1. Bacteriophages 2. Plant viruses 3. Animal viruses |
| ICTV system in classification | 1. type and structure of genome 2. method of genome replication 3. host range 4. other physical or chemical characteristics (shape, capsid chemistry, etc) |
| What are the types and structure of genome? | 1. DNA (ss + or - sense, ds +/- sense) 2. RNA (ss + or - sense, ds +/- sense) |
| What are the methods of genome replication? | 1. host enzymes (all) 2. viral and host enzymes (some enzymes that facilitate replication) |
| How is + sense RNA processed? | By host ribosome just like mRNA |
| How is - sense RNA and ds RNA processed? | viruses are copied into + sense RNA by viral RNA Polymerase within the host |
| What do RNA-DNA viruses contain? | 1. contain one or more copies of + sense RNA 2. capsid 3. reverse transcriptase 4. retroviruses |
| How does reverse transcriptase work? | 1. uses RNA as template to form complimentary DNA strand 2. ss DNA is then replicated by host enzymes to form ds DNA 3. ds DNA can then become part of host chromosome for a period of latency |
| What are examples or a retrovirus? | HIV and HTLV-1 |
| DNA viruses - how is ds DNA processed? | by host RNA polymeraseto form mRNA |
| How is ss DNA processed? | 1. in the host's replication enzymes to form ds DNA 2. ds DNA is then transcribed into mRNA by host enzymes |
| What are the steps of Viral replication? | 1. Adsorption 2. Penetration 3. Synthesis 4. Maturation 5. Release |
| What is adsorption? | when the virus becomes attached to the surface of the target cell |
| What is penetration? | Bacteriophage - genome is not engulfed, it is injection into the host cell Animal viruses - are completely engulfed and then the virus must be uncoated to expose the genome |
| What is synthesis? | new nucleic acids, capsid proteins, and other viral components are formed |
| What is maturation? | assembly of newly synthesized viral components into complete virions |
| What is release? | departure of new virions from the host cell either by bursting or budding from the cell |
| What are bacteriophages? | 1. viruses that infect bacterial cells 2. can contain dsDNA, ssDNA or RNA 3. T-even phages (T4) |
| What is the complex structure of T(4)? | 1. head with genome 2. tail (contains lysozyme) 3. tail fibers 4. pins |
| What are the three types of phages? | bacteriophages, virulent phages and temperate phages |
| Virulent phages | 1. induce lytic cycle 2. burst time is 20-40 minutes 3. particles released is 50-200 |
| What is burst time? | time it takes from when the virus first infects the cell to when the particles are released |
| temperate phages | 1. do not immediately induce lytic cycle 2. majority of time they are in lysogeny 3. prophage 4. lysogen 5. lysogenic conversion 6. environmental stresses will eventually induce lytic cycle |
| What is prophage? | viral DNA within the bacterial chromosome - part of DNA that fits into the host chromosome |
| What is lysogen? | the combination of the bacterium and a temperate phage |
| What is lysogenic conversion? | the ability of a prophage to prevent additional infections of the same cell by the same type of phage |
| Phage Growth : Growth Curve What are the phases of the growth curve? | 1. eclipse period 2. latent period 3. viral yield |
| What is the eclipse period? | period from penetration through the synthesis of new particles |
| What is the latent period? | period from penetration through particle release |
| What is viral yield? | the numbers of particles typically released |
| Phage Enumeration : Process of Plaque Assays | 1. They are serial dilutions. 2. Samples are innoculated onto lawn of susceptible bacteria 3. Counting of clear zones rather than colonies after incubation 4. Computation of sample on plate |
| What is the computation equation? | (# of plaques x dilution)/mL spread over plate pfu / mL |
| Animal Virus Replication | 1. adsorption to cell membrane 2. penetration of entire virion by endocytosis or fusion 3. uncoating of particle to expose viral genome 4. synthesis (DNA viruses in nucleus and RNA viruses in cytoplasm) 5. maturation 6. release via budding or lysis |
| What is different between animal viruses and bacteriophage? | Virus particles are completely penetrated in animal cells whereas just the genome information is injected from the bacteriophage into the cell. |
| Penetration of animal viruses | most naked viruses enter the cell by endocytosis |
| What is uncoating? | occurs after animal virus enters the host cell's cytoplasm and separates the genome from the protein coat |
| What is more common penetration for naked viruses? | endocytosis |
| What is more common for enveloped viruses? | fusion |
| Synthesis : How do DNA animal viruses replicate? | - replicate their DNA in host cell nucleus with aid of viral enzymes - synthesize their capsid in the cytoplasm with the aid of host cell enzymes |
| How are RNA animal viruses synthesized? | - (+) sense RNA acts as mRNA - dsRNA (+) sense are transcribed into ssDNA with the help of reverse transcriptase - (-) sense RNA make (+) sense RNA which are used as mRNA |
| What is maturation? | the assembly of the viral components into complete virions |
| What are latent viral infections? | when dsDNA viruses exhibit a lytic cycle and are activated by environmental stresses after being dormant. |
| What is the cytopathic effect (CPE)? | the invisible effect viruses have on cells - changes in cell shape and detachment from adjacent cells or culture container - can be so distinctive that a virologist can specific infecting virus |
| What is syncytia? | giant, multinucleated cells caused by fusion of adjacent cells |
| What is teratogenesis? | embryonic defects induced suring pregnancy |
| What is a teratogen? | drug or other agent that induced embryonic defects |
| TORCH | series of tests used to test for defects |
| Human viruses that account for many defects | cytomegalovirus herpes simplex virus I and II rubella |
| What are virus-like agents? | They are not viruses. viroids and prions |
| What are viroids? | - small molecule of circular RNA in nucleoli -interferes with hosts ability to process mRNA |
| What are prions? | - improperly folded proteins - clump together in fiber-like mass in cell - cause progressive loss of mental facilities and motor function |
| What are the six ways that viroids are different from viruses? | 1. single circular RNA molecule 2. exists inside cells as naked RNA 3. don't require helper virus 4. viroid RNA doesn't produce proteins 5. viroid RNA is always copied in host nucleus 6. not apparent in infected tissue w/o use of special techniques |
| What are the 5 things a microorganism must do to cause disease? | 1. gain access to target host in sufficient numbers 2. evade/survive host defenses 3. invade target tissues and cells 4. adhere to and colonize target cell surfaces 5. release toxins or other harmful metabolic products |
| What are virulence factors? | physical and physiological characteristics of pathogenic organisms that help them to infect and cause disease in host. |
| What are sources of pathogens? | True pathogens, Opportunistic pathogens, Exogenous and Endogenous |
| What are True Pathogens? | -non-native flora that cause disease in healthy hosts -specific, recognizable diseases |
| What are Opportunistic Pathogens? | - normal flora - cause disease when host defenses are compromised or when in an area unnatural to them |
| What is Exogenous? | - external environment - contact with infected persons or animals |
| What is Endogenous? | - normal flora - latent infections |
| What are portals of entry? | - skin (fomite penetration) - cuts, burns, abrasion or needles - respiratory tract (inhalation) - gastrointestinal tract (ingestion) - urogenital tract (sexual transmission) - conjunctiva (ocular region) |
| What is the infectious dose? | minimum number of cells necessary to induce infection and then disease |
| Info about infectious dose | - organisms smaller than IDs are more virulent (potent) - if number of cells entering host is below ID, an infection will not occur - if ID is exceeded, infection and then disease can set in rapidly |
| What are the antiphagocytic factors the evade host defenses? | - slime layer or capsule that prevents phagocytosis - parasitophorous vacuoles - enable certain organisms to survive within phagocytes - leukocidins (substances toxic to WBCs) and other cytotoxic substances |
| What is invasion? | release of digestive enzymes or other factors that facilitate the spread of and/or penetration of the pathogen into target cells |
| What are adhesion mechanisms? | -fimbriae -adhesions(proteins/glycoproteins on pili and capsules) -slime layers -viral spikes -capsid proteins |
| What colonization? | growth on epithelial cells, mucous membranes, other tissues |
| What happens on Biofilm development? | -population increase -evasion of host defenses |
| What are the two types of effects on damage and disease? | indirect effects and direct effects |
| What are indirect effects? | - opportunistic pathogens - stimulation of an excessive or inappropriate host response -example is the capsule on strepto pneumoniae and fluid build up on the lungs |
| What are direct effects? | - true pathogens - damage to cells, tissues and organs such as enzymes and toxins |
| What type of effects do endotoxins have? | systemic effects |
| What are examples of endotoxins? | -gram negative cells -LPS (Lipid A) -Induce fever, decrease BP, can cause tissue damage |
| What type of effects do exotoxins have? | specific effects that are more powerful |
| What are examples of exotoxins? | -small proteins secreted by G+ and G- pathogens -immunotoxins(leukocidins, leukostatins, hemolysins) -neurotoxins (nervous system) -eneterotoxins (gut) -toxemia - spreadof endotoxins from site to infection |
| What are types of antimicrobial agents? | - chemotherapy - antimicrobial agents - antibiosis - antibiotic - synthetic/semi-synthetic drugs |
| What is chemotherapy? | the use of chemical substances to treat various aspects of a disease |
| What are antimicrobial agents? | a special group of chemotherapeutic agents used to treat diseases caused by microbes |
| What is antibiosis? | literally means "against life" |
| What is an antibiotic? | a chemical substance produced by microbes which has the capacity to inhibit or destroy the growth of bacteria/other microbes |
| What happened in early history? | there were traditional healers |
| What happened in 1910? | Paul Ehrlich used Salvarsan to treat syphillis |
| What happened in 1928? | Alexander Fleming identified PCN |
| What happened in 1935? | Gerhard Domagk discovered prontosil, a red dye, inhibits growth of many G+ bacteria |
| What happened in 1936? | Ernest Fourneau discovered that the sulfanilamide portion of protonsil contained antimicrobial activity ~ led to sulfa drugs |
| What happened in the 1940s? | Ernest Chain and Howard Florey isolated PCN and helped in getting it mass produced |
| What are properties of antibiotics? | - selective toxicity - the spectrum of activity - modes of action - side effects - the resistance of microorganisms |
| What is selective toxicity? | - the antimicrobial agent must harm the microbes without causing significant damage to the host |
| What is toxic dosage level? | the level of toxicity that causes host damage |
| What is therapeutic dosage level? | the level that successfully eliminates the pathogenic organism if the level is maintained |
| What is the chemotherapeutic index? | (maximum tolerable dose/kg body weight)/(minimum dose/kg body weight) |
| What is spectrum of activity? | the range of different microbes against which an antimicrobial agent acts |
| What is broad spectrum? | agents effective against both G+ and G- bacteria |
| What is narrow spectrum? | agents effective against a small number of microbes |
| What are the actions of antibiotics? | -antibiotic action on an important structure or function of a pathogen that is different from the host - actions are either bacteriocidal or bacteriostatic -host immune system must still complete elimination of pathogen |
| What are the 5 Mode of Action? | 1. Inhibition of cell wall synthesis 2. Disruption of cell membrane function 3. Inhibition of protein synthesis 4. Inhibition of nucleic acid synthesis 5. Action of antimetabolites |
| Examples of Inhibition of cell wall synthesis | PCN, bacitracin, cephalosporin, vancomycin |
| Examples of Disruption of cell membrane function | polymysin |
| Examples of Inhibition of protein synthesis | tetracycline, erythromycin, streptomycin, chloramphenicol |
| Examples of Inhibition of nucleic acid synthesis | rifamycin, quinolones, metronidazole |
| Examples of Action as antimetabolite | sulfonilamide, trimethoprim |
| What happens in Inhibition of Cell wall Synthesis? | -selectively damages bacterial cells -PCN and cephalosporin contain Beta lactim ring -the Beta lactim ring attaches the enzymes that cross-link PTG and prevents cell wall synthesis |
| What happens during Disruption of Cell Membrane? | - acts as detergents-lower surface tension and affect pH and distort the bacterial cell membrane -bind to phospholipids in the membrane -highly effective against G- bacteria which have an outer membrane -certain polypeptide antibiotics, such as polymyx |
| What happens during Inhibition of Protein Synthesis? | attack bacterial cells w/o significantly damaging animal cells -can affect mitochondria -example of selective toxicity |
| What happens during Inhibition of Nucleic Acid Synthesis? | -take advantage of the differences between the enzymes used by bacterial and animal cells to synthesize nucleic acids -Rifamycin family binds to bacterial RNS polymerase in inhibits RNA transcription |
| What is Action as Anti-Metabolites? | -substances that affect the utilization of metabolites and prevent pathogen from carrying out certain metabolic reactions |
| What are the two ways that Anti-metabolites function? | 1. competitively inhibiting enzymes 2. erroneously incorporated into important molecules such as nucleic acids |
| What are side effects of antimicrobial agents? | -toxicity -allergy -disruption of normal microbiota |
| What is toxicity? | when certain antibiotics exert toxic effects on patients, even at low dosage |
| What are some symptoms of toxicity? | nausea, diarrhea, light sensitivity, kidney damage |
| What is an allergy? | response of the body's immune system to foreign substances (antigen) |
| What are allergic symptoms? | itching, rash, hives |
| What is disruption of natural flora? | killing native flora, allowing opportunities for invasive species to infiltrate the body |
| What is a super-infection? | when being treated for for infection, the invasive species can have a competitive advantage |
| How do microorganisms acquire resistance? | mutation, lateral gene transfer and natural selection |
| Do antibiotics cause resistance? | NO |
| What do antibiotics create? | an environment favorable for the resistant organisms to infect and proliferate |
| What are the 5 Mechanisms of Resistance? | 1 alteration of targets 2 alteration of membrane permeability 3 development of enzymes 4 alteration of enzymes 5 alteration of metabolic pathway |
| What is alteration of targets? | -chemical alteration of structures of enzymes and proteins -causes alteration in the target and can no longer bind |
| What is alteration of membrane permeability? | decrease of ability of antibiotics to get in |
| What is development of enzymes? | -pick up genes that code for new enzymes through lateral gene transfer -may include gene that codes for B-lactim ring |
| What is alteration of enzyme? | no longer react with substrate |
| What is alteration of metabolic pathway? | one reaction has changed in a series of reactions |
| What is cross resistance? | refers to the pathogenic resistance to two or more similar antimicrobial agents by way of common mechanism |
| What are examples of cross resistance? | - alteration of ribosomal protein via mutation may render a variety of drugs that inhibit protein synthesis ineffective - an enzyme that will break down one B-lactam ring antibiotic will break down other B-lactam ring antibiotics |
| What is limiting drug resistance? | prescribed levels should remain in a patient long enough to inhibit pathogens or decrease their numbers to well below infectious dose |
| What is synergism? | two antibiotics can be given simultaneously to minimize the effectiveness of resistant pathogens |
| Kerby Bauer Method / Disk-Diffusion Method | semi-quantitative |
Created by:
ckunkel2011
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