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37 Cards in this Set
- Front
- Back
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All viruses are - Obligate intracellular parasites |
viruses absolutely require living host cells in which to multipy |
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Generalized viral life cycle |
-Infect cell -replicate within host cell -leave cell -infect new cell |
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Describe general characteristics of viruses |
-all are obligate intracellular parasites -all have single type of nucleic acid, DNA or RNA, never both -all have protein coat (capsid) -ultramicroscopic -lack enzymes for metabolic function |
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Host cell |
cell infected by virus |
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Capsid |
protein coat that surrounds the viral nucleic acid - all viruses have capsid |
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Envelope |
found in some viruses capsid is surrounded by membrane made of lipid bilayer and some protein |
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Host range |
specific kinds of cells that the virus can infect - viral specificity |
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Virus morphology |
1. Helical - appears rod shaped 2. Polyhedral - many sided (icosahedral - 20 sided-most common 3. Complex - complicated structures 4. Enveloped - roughly sperical |
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Describe characteristics used to classify viruses |
1. nucleic acid types 2. strategy for replication 3. morphology 4. host range taxonomic groups - order, family, genus, species |
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Bacteriophage (phage) |
-viruses that infect bacteria -phages can multiply in two different cycles, lytic and lysogenic |
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Lytic Cycle |
1. Attachment (absorbtion) 2.Penetration 3. Replication (biosynthesis) 4. Assembly (maturation) 5. Release |
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Lytic Cycle attachment |
-phage attaches to host cell -requires specific binding between external surfaces of virus and host cell |
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Lytic cycle penetration |
entry of viral nucleic acid into host cell cytoplasm |
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Lytic cycle replication |
-components of new virus synthesized a. bacterium stops synthesizing its own molecules, and starts synth. viral molecules b. replication of viral DNA using host DNA polymerase and nucleotides c. transcription of viral genes using host RNA polymerase and nucleotides d. translation of viral mRNA |
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Lytic cycle assembly |
mature virus particles spontaneously assemble from newly synthesized parts |
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Lytic cycle release |
virus induced lysis of host cell |
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Lysogenic Cycle |
1. attachment - same as lytic 2. penetration- same as lytic 3. Virus is not replicated, viral DNA becomes part of host cell chromosome -the inserted DNA is called prophage -virus lies dormant as silent infection |
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Transduction |
phage can serve as transporters of bacterial genes between bacterial cells |
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Explain what occurs during transduction |
1. Bacterium #1 in infected by phage 2. Phage disrupts bacterial DNA and replicates new phage 3. During assembly of new phage, sometimes, phage mistakenly incorporates bacterial DNA into newly synthesized cell 4. Phage (with bacterium #1 DNA) is released from cell. |
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What are the two superfamilies of animal viruses? |
1. DNA viruses 2. RNA viruses |
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Animal Virus Life Cycle - attachment |
-attachment of virus to cell surface via protein binding --interaction is specific and limited and determines host range and tissue specificity |
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Animal Virus penetration |
-both the capsid and nucleic acid enter the host cell cytoplasm -occurs in two ways- endocytosis and fusion |
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Animal virus replication |
-viral genome controls host synthetic and metabolic machinery -shuts down host synthesis |
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Animal virus assembly |
usually spontaneous |
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Animal virus release |
lysis of host cells |
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Uncoating |
because the capsid and nucleic acid enter the host cell cytoplasm, the capsid and envelope must be removed |
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Budding or exocytosis |
the exiting virus is surrounded by a piece of cell membrane which becomes its envelope |
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Cytopathic Effects (CPE's) |
virus induced damage to cell that alters microscopic appearance. can be used to diagnose a viral infection |
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Provirus |
inserted viral DNA |
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Neoplasia |
uncontrolled cell division |
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Name two human cancer viruses |
-Human papilloma virus (HPV)- causes cervical cancer -Hepatitis B virus - causes 80% of liver cancers |
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Oncogenic virus |
cancer causing virus |
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Oncogenes |
cancer causing genes |
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3 types of DNA viruses |
1. Poxviridae - smallpoxvirus casues small pox 2. herpesviridae - simplexvirus, herpes simplex 2 - causes gential herpes 3.hepadnaviridae - hepatitis B - causes liver cancer |
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3 types of RNA viruses |
1. orthomyxoviridae - infuenzavirus, infuenza virus A causes the flu 2. retroviridae - lentiviruses, HIV, causes AIDS 3. picornaviridae - rhinovirus, causes the common cold |
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Prions |
-smaller than a virus -infectious, self-replicating protein -no nucleic acid present -all involve fatal neurological degeneration ex. mad cow disease |
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Viroids |
-extremely small, circular pieces of RNA that is infectious and pathogenic to plants |
