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91 Cards in this Set
- Front
- Back
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Name the basic characteristics of viruses.
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- obligate intracellular parasites
- reproduce by assembly of new components (not by cell division) - Cannot make energy or proteins on their own - Genomes contain DNA or RNA, but NOT both - Lack true cellular structure. |
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What is a virion?
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Complete, fully assembled virus particle.
Form of virus that exists outside of host cell Facilitates transmission of virus from one hot to another |
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What are two types of structurally distinct types of viruses?
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Non-enveloped and enveloped.
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What are the following characteristics of NON-ENVELOPED viruses?
- genome? - capsid? |
Genome: DNA or RNA
Capsid: protein coat surrounding genome |
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What is a nucleocapsid?
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Genome + capsid
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What are the following characteristics of ENVELOPED VIRUSES?
- genome? - capsid? - envelope? |
genome: RNA or DNA
capside: protein coat surrounding genome envelope: membranous structure surrounding nucleocapsid (membrane + viral glycoproteins) |
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What are the two major capsid types?
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Icosahedral: 20 sides composed of 12, 5 sided units
Icosadeltahedral - larger more complex variation of icosahedral (but still has 20 faces). !2 pentamers and variable number of six sided subunits along edges and across faces. |
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Describe a helical capsid.
Genome? Capsid? Helical viruses that infect humans? |
Overall cylindrical appearance.
Genome arranged in tightly coiled spiral. Capsid proteins positioned along genome and usually closely associated with it Helical virsus that infect humans have RNA genomes. |
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What is the function of the capsid that is clinically relevant?
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In non-enveloped viruses, capsid is the outermost layer and thus enables virus to survive effectively outside of host. Direct contact is not necessary for transmission.
Facilitates transmission of disease via FOMITES, air, hand-to-hand contact, fecal-oral route, etc Comparatively hard to inactive with detergents, disinfectants. |
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What is the chemical composition of viral envelopes?
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Phospholipds, proteins, glycoproteins
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What is the structure of a viral enveloped?
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membranous (lipid bilayer)
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Where is the viral envelope derived from?
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the host cell membrane but modified by virus.
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What is the most important function of the glycoproteins in the viral envelope?
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Serve as viral attatchment proteins (VAPs)
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What is a VAP?
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Viral attachment proteins - bind to receptor on surface of host cell
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What is a hemagglutinin?
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bind to erythrocytes and causes clumping of RBCs
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What are the major differences between the envelope and capsid of a virus?
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Envelopes are:
- environmentally fragile and must remain in aqueous environment to maintain structure and infectivity Enveloped viruses are not easily transmitted via fecal-oral route, on fomites or through air. They are inactivated in GI tract, detergents, drying, heat. Usually transmitted in secreted body fluids by blood-to-blood transfer. |
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What are the steps in the viral replication cycle?
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1. Recognition of and attachment to host cell.
2. Penetration: entry of virus (or part thereof) into cytoplasm of host cell. 3. Uncoating: release of genome inside of host cell. 4. Macromolecular synthesis: production of new virus components (genomes, proteins, etc) 5. Assembly: assembly of components to produce new viruses. 6. Release: exit of new virions from host cell. |
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How do non-enveloped viruses recognize and attach? What about enveloped ones?
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Non-enveloped: capsid protein acts as VAP or some other structure mediates attachement.
Enveloped: specific envelope glycoproteins function as VAPs |
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What is tropism?
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range of tissue types that viruses can infect.
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How do most viruses penetrate host cells?
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Endocytosis. Virus taken into cytoplasm enclosed in membrane bound vesicle.
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How to non-enveloped viruses mediate penetration?
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Viropexis: binding between VAPa nd receptor causes three-dimensional conformation changes of capsid proteins, etc.
Hydrophobic portions of capsid proteins exposed by conformation changes. Hydrophobic surgaces facilitate passage of virus through hydrophobic core of cell membrane. |
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What is viropexis?
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The way by which non-enveloped viruses penetrate host cells.
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How to enveloped viruses mediate penetration? (2 ways)
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1. Fusion at cell surface: viral envelope membrane fuses with host cell cytoplasmic membrane.
Nucleocapsid (minus envelope) released into cytoplasm. 2. Fusion with endosome membrane: entire virion brought into cell via endocytosis. Viral envelope membrane fuses with endosome membrane, releasing nucleocapsid into cytoplasm. |
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How does uncoating occur for NE viruses that penetrate by viropexis?
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Attachement to host cell receptor weakens capsid and initiates uncoating.
All or most of cpasid left behind as viruses pass. |
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How does uncoating occur for NE viruses that penetrate by endocytosis?
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Acidic conditions and/or degradative enzymes in endosome may promote deterioration of capsid.
Endosome may fuse with lysosome and lysosomal enzymes |
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How does uncoating occur for E viruses?
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Fusion with host cell cytoplasmic or endosomal membrane removes envelope.
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What is transcribed first during virus replication?
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Early mRNAs that code for early gene products
these are needed to carry out some viral replication cycles |
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How does transcription of DNA viruses occur?
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in nucleus of host cell.
Uses host cell's DNA-Dependent RNA polymerase and other enzymes to synthesize viral mRNAs. Regulated by interaction of DNA binding proteins with promoter and enhancer elements in viral genome. |
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What are the basic requirements for genome replication?
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Nuclear factors that recognize ori site (provided by host cell or encoded by virus)
DNA-dependent DNA polymerase to copy DNA (provided by host cell or encoded by virus) Primer: required by DNA polymerase to initiate DNA synthesis (provided by virus, but detailed mechanism varies). |
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What is special about Transcription and replication of RNA VIRUSES?
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Need RNA dependent RNA polymerase enzymes to copy RNA
Host cell has no means of replicating viral RNA Virus must either carry enzymes in virion or code for their production shortly after entering cell. |
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How does transcription occur in positive-senss ss-RNA viruses?
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Viral genome (+ sense strand) itself can function as mRNA in host cell.
Viral genome binds to host-cell ribosomes and directs production of viral proteins. Ribos cant distinguish bw host and viral mRNA Viral genome initiates infection by itself. Virus doesnt have to provide RNA-dependent RNA Polymerase to start process (DOESNT NEED TO CARRY ENZYME IN VIRION) No need for transcription to take plasce if viral genome functions directly as mRNA. |
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How does transcription occur in negative sense ss-RNA viruses?
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The viral genome cannot serve as a mRNA as in positive sense.
Virus must provide RNA-dependent RNA polymerase to carry out transcription (polymerase must be carried in virion; enters host cell with genome) Polymerase copies parts of genome to --> mRNAs |
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How does genome replication occur in postive sense ss-RNA viruses?
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One protein is made when ribosomes read viral genome as mRNA: viral RNA-dependent RNA polymerase.
Enzyme copies + sense genome to produce - sense strand of RNA - strand serves as template to multiple + strands (new copies of the genome) |
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How do retroviruses function?
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They are +sense ss-RNA but instead of acting as mRNA, genome is converted to DNA by RNA-dependent DNA polymerase (reverse transcriptase)
Virus must provide enzyme |
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How does transcription and genome replication occur in retroviruses?
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Viral genome in host cell chromosome functions just as single cellular gene does -- under certain circumstances, host cell's DNA dependent RNA polymerase transcribes viral genome --> full length + strand RNA
Multiple copies of transcripts used as copies of genome when new viruses assembled. Transcripts also function as viral mRNA. |
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What are some tactics used to get host cells to translate viral mRNAs in preference to host mRNAs?
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1. produce large quantities of viral mRNAs (tie up host ribos with viral scripts)
2. Block host mRNAs from leaving nucleus of cell (adenovirus) 3. Degrade host cell's mRNAs (herpes) 4. Modify ribos to prevent binding of mRNAs (poliovirus) |
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Where is the nucleocapsid assembled? (DNA viruses? Pox and RNA viruses?)
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Site of nucleocapsid assembly related to site where genome is replicated.
DNA: assmebled in nucles of host cell Pox and RNA: assembled in cytoplasm |
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What are inclusion bodes?
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stainable structures in the nucleus or cytoplasm in some viruses.
From changes in membrane or other cell structure or more often from accumulation of viruses. |
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What is budding?
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enveloped viruses acquire envelopes by budding through host-cell membrane.
different types of viruses bud through cytoplasmic membrane, golgi membrane, nuclear membrane, or endoplasmic reticulum. |
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When do errors in viral replication occur most frequently?
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During assembly.
Can result in empy virions or virions with defective genome |
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What are defective particles?
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noninfectious virions
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How do NE viruses leave the host cell?
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lysis of host cell
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How do E viruses leave the host cell?
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lysis or exocytosis.
Some E viruses bud through host cell's cytoplasmic membrane (simultaneous addition of envelope and release) -- this is how they get their envelope. |
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What is viremia?
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transport of viruses through bloodstream (occurs during many viral diseases)
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What are two ways that viruses can gain access to bloodstream or lymphatic system?
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Uptake by macrophages following tissue damage at primary site of infection.
Traansport past mucoepithelial cells of oropharynx, GI tract, etc. |
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What is secondary viremia?
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when replication of some viruses in endothelial cells, macrophages or liver lead to second amplification of viruses.
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How can viruses gain access to the CNS?
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From bloodstream
Migration of infected macrophages From infected meninges or CSF Infection of peripheral or sensory and subsequent neuronal transport. Infection of mucoepthelium, skin, or muscle --> innervating neuron --> CNS brain |
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What are the three possible outcomes of viral infection of cell?
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abortive infection: failed infectionl replication of virus that does not occur (often due to defective mutant virus)
Lytic infection: viral replication proceeds and results in sudden death of host cell Persistent infection: replication or partial replication occurs without death of host cell. |
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What is a non-permissive cell?
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does not permit replication of particular type of virus (may lack receptor on surface or lack metabolic machinery needed by virus)
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What is a permissive cell?
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supports complete replication cycle of particular type of virus
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What is a semipermissive cell?
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typically supports some but not all steps in viral replication.
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What is a syncytia?
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a multinucleated giant cell which is formed when the expression of viral glycoproteins on surgace of host cell sometimes cause fusion of host cells.
Virus evades antibodies by remaining intracellular |
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What are oncogenic viruses?
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some DNA and retroviruses causes persistent infections that stimulate uncontrolled cell growth, causes transformation (immortalization) of cell.
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What is transformation (immortilization)? What is are characteristics of immortalized cells?
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An immortalized cell is one that is undergoing uncontrolled cell growth as caused by a virus.
Characteristics: - continued growth without senescence - altered cell morphology and metabolism - increased growth rate and sugar transport - loss of cell-contact inhibition of growth. |
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In what kind of cell does immortalization occur?
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semi-permissive
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Name two examples of an oncogenic virus?
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- Papillomavirus: codes for proteins that inactivate cells growth recualtor porteins, such as p3
Epstein-Barr: stimulates growth of B cells and induces expression of bcl-2 oncogene (prevents apoptosis) |
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What is the primary role of fungi in nature?
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They serve as saprobes that degrade dead and organic matter and help to recycle carbon.
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What does "opportunistic pathogens" mean?
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Microbes that cause disease only under certain circumstances, typically in hots who are weaken/compromised.
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What are mycoses?
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Fungal diseases
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What are the basic biological characteristics of fungi?
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Eukaryotic cell structure
Rigid Cell wall composed of CHITIN and GLUCAN Cell membranes use ERGOSTEROL intead of cholesterol as major sterol Heterotrophic metabolism Mostly aerobic, but some are facultatively (carry out fermentations) or strictly anaerobic. |
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what is the rigid cell wall of fungi made from?
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Chitin
Glucan |
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How do yeast reproduce?
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Yeast are unicellular fungi that reproduce by budding (an asymmetric form of cell division)
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What are hyphae?
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branching filaments of MOLD that only elongate at tips
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What are septate?
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cells in filament separated by cross walls in MOLD
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What are coencytic?
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hollow filaments with multinucelate cytoplasm and no cross walls in MOLD
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What are vegetative hyphae?
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embedded in or on surface of growth medium; serve to absorb nutrients in MOLD
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What is aerial hyphae?
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project above surface of growth medium, usually serve to distribute spores. MOLD
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What are mycelium?
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mass of intertwined hyphae in MOLD
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What are dimorphic fungi?
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fungi that can exist in both yeast and mold forms, depending on environmental conditions.
Many of the medically important fungi fall into this category (Candida) |
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What are pseudohyphae?
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Chains of elongated cells that look like linked sausages.
Odd form of budding in which new cells dont pinch off from parent. New cells elongate instead of assuming oval shape. Lateral buds often form at junctions between long cells. Candida (dimorphic fungi) frequently produce these. |
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What is a superficial mycoses?
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limited to the very superficial surfaces of skin and hair (non-destructive, of cosmetic importance only)
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What are cutaneous mycoses?
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FUNGI - infections of keratinized layer of skin, hair, and/or nails.
May elicit host response and become symptomatic. Itching, scaling, broken hairs, discolored nails |
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What are subcutaneous mycoses?
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FUNGI - affect deeper lays of skin, as well as connective tissue, muscle, and/or cornea
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What are endemic mycoses?
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Fungi that cause primary infection in lungs, with possible dissemination to other organs and tissues (aka systemic mycoses)
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What are opportunistic mycoses?
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caused by fungi normally found in the environment or living as commensals of humans; occur mostly in immunocompromised or debilitated individuals.
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What are some characteristics of the protozoa group?
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Unicellular
Nucleus contains central karyosome Various mechanisms for motility Medically important phyla include ameoba, flagellates, ciliates, and sporozoa. |
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What pathogen belongs to Chromista?
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blastocystis hominis
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What are some characteristics of the microspora group?
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Classified as fungi
small intracellular parasites that lack mito spores have polar tube to inject infectious material into host cells |
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What are some characteristics of the helminths group?
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complex organisms with elongated bodies and bilateral symmetry ("worms")
Medically important subgroups: Nematodes flatworms: flukes, tapeworms |
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What are the differences between trematodes and nematodes?
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Nematodes are round, flukes are flat.
Nematodes have separate sexes (trematodes/flukes do not) Nematodes have complete digestive systems (flukes do not) Nematodes infect intestines and blood Flukes infect liver, lungs, GI tract or blood |
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What are cestodes?
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parasitic flatworms with ribbon like bodies (tapeworms)
No separate sexes Lack digestive systems (absorb nutrients through their wall) Bodies are segmented into proglottids |
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What is the first step in replication process of viruses?
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recognition and attachment
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What does recognition and attachment of viruses involve? For NE? For E?
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highly specific binding of VAP or other viral structure to receptor molecule on host cell.
Host cell receptors: proteins, carbs on glycoproteins or glycolipids Non enveloped viruses: capdis protein acts as VAP or some other structure mediates attachment. Enveloped: specfic envelope glycoproteins serve as VAPs |
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What is the difference between host range and tropism?
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Host range is the range of SPECIES a virus can infect.
Tropism is the range of TISSUES a virus can infect. |
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What are the stages in a typical viral disease?
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Prodromal
Acute - period during which characterisitc signs and symptoms of disease present.Disease peaks in severity at this point. Convalescence - symptoms disappear. Persistant infection/chronic disease |
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What is the prodromal period of viral disease/.
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period in which nonspecific symptoms appear
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What must a tissue have to serve as primary site of infection?
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Must have right type of receptor on surface.
Must have appropriate biosynthetic material |
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What is primary site of infection for most viral pathogens of humans?
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oral mucosa and upper respiratory tract
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What is dissemination?
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Viruses disseminate from primary tissue to other tissues.
This usually occurs through the bloodstream or lymphatic system |
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What is viremia?
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transport of viruses through bloodstream
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What are the possible fates of viruses taken up by phagocytic macrophages?
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Inactivation
Replication inside of macrophage Delivery to ultimate target tissue of virus |
