TAMU BIOL 206 Exam 2 Questions and Answers correct

TAMU BIOL 206 Exam 2 Questions and Answers correct Characteristics of Viruses that Differ from Cells - no metabolism - no reproduction - acellular - either DNA OR RNA (not both) - double or single stranded DNA or RNA - smaller than a cell - proteinaceous capsid around genome; some have envelope around the capsid - replicate in an assembly line - no ribosomes - no ATP- generating mechanism - are infectious Herpes - cold sores - genital herpes - chicken pox - ALL painful HPV (human papilloma virus) - causes large % of warts in humans Two Capsid Structure Types: Helical and Polyhedral Capsid - protein coat that encloses and protects the nucleic acid - constructed from identical protein subunits called capsomeres - the capsid together with the nucleic acid form the nucleocapsid Helical capsid structure continuous helix of capsomers forming a cylindrical nucleocapsid Polyhedral (Icosahedral) (20 sided with 12 corners) - vary in the number of capsomers - each capsomer may be made of 1 or several proteins - some are enveloped - membrane external to capsid (envelope made of host cell membrane) The viral envelope - derived from host cell membrane - some animal viruses - not on bacteriophages bc bacteria have cell walls - acquired when the virus leaves or buds through the host cell - exposed proteins on the outside of the envelope called spikes/pelomers Naked Virus virus without an envelope Spikes/pelomers are essential for... binding to receptor and infectivity of the host cell Proteins on nucleocapsid or envelope interact with _______________ host cell receptors complementary Functions of the envelope - protects the nucleic acid when the virion is outside the host cell - is used to: bind to receptor and infect the host cell Advantages of the envelope - is similar to host membranes so helps virus evade host immune response for a time Molecular Mimicry advantage of envelope - virus looks like host cell What is required for infectivity? envelope - fuses with host cell membrane No envelope = No infectivity Disadvantage of virus envelope - anything that damages a cell membrane will damage the viral envelope Environmental conditions like temp, ph, pressure, toxins, detergents, etc can damage the viral envelope which results in __________ infectivity naked viruses are more ___________ to the environmental factors resistant Why is resistance to environmental conditions important? viruses with a damaged/destroyed cell envelope cannot interact with (complementary) molecule/host receptor Viruses must be grown in what type of cells? living Animal viruses may be grown in living animals or in _____________ eggs or in ____ __________. embryonated cell cultures (continuous cell lines) ____________________ form plaques on a lawn of bacteria Bacteriophages In order for infection to occur..... all viruses must interact with host cell receptor 1) host receptor is complementary to molecule on virus 2) viruses are non motile 3) chemical attraction involved = sense presence of host cell Replication of Animal Viruses entry and uncoating - at least three different mechanisms by which animal viruses enter a cell direct penetration only nucleic acid enters host cell - naked viruses only - capsid stays on the outside membrane fusion only nucleocapsid enters - enveloped viruses only endocytosis only enveloped virus or naked virus enters cell Viruses are _________ specific! Viruses are _________ specific! species tissue Some receptors are only for ____________ endocytosis - some spikes look like amino acids that the cell needs which makes it confusing for the receptor Viruses that enter cell with capsid intact are __________ inside the cell uncoated Genome/NA has to be released into the cytoplasm for ______ ___________ - enzymes needed viral replication Budding/Blebbing exocytosis; nucleocapsid binds to membrane which pinches off and sheds the viruses gradually - enveloped viruses bud out - Lysis viruses released when cell dies and ruptures - naked viruses Some Bacteriophages have a________ ____________along with a ______ _____ and attachment fibers polyhedral nucleocapsid helical tail Most widely studied bacteriophages are those that infect ________ E. coli Multiplication Cycle of Bacteriophages - similar stages as animal viruses - only the nucleic acid enters the cytoplasm - release due to cell lysis Host Cell Infection is due to.... affinity of viral surface proteins for complementary proteins (receptor) on host cell surface no host receptor = ? no binding/ no infectivity The host range is determined by the presence of the _________ receptor/ complementary molecule Host range examples rabies virus - most mammals T4 bacteriophage - only infect E. coli 5 Steps in Phage Replication Order 1) Attachment 2) Penetration 3) Biosynthesis 4) Maturation 5) Release Attachment binding of virus to specific molecule/receptor on host cell Penetration genome/nucleic acid enters host cell Biosynthesis viral components produced - making enzymes that are needed, makes NA for progeny Maturation assembly and completion of viral formation Release viruses leave cell via lysis to infect other cells Burst time: Burst size: :time from attachment to lysis :# of viral particles released - between 50 and 300 virions Details of bacteriophage T4 infecting E. coli T4 produces lysozyme = weakens E. coli's cell wall to allow viral tail penetration - LPS is receptor for T4 on E. coli Temporate Virus 2 lifecycles (lytic vs. lysogenic) Lytic Phase - "bad roommate" - happens when cell conditions are unfavorable for the virus - ex: UV radiation, extreme heat Lysogenic Phase conditions are good, so virus wants to stick around Lysogeny or temperate phages undergo absorption and penetration, but don't _________ replicate (only partakes in the first 2 steps of the lytic cycle) Prophage the viral DNA that is embedded in the host cell's DNA Lysogenic Cycle prophage is retained and copied during normal cell division resulting in the transfer of temperate phage genome to all host cell progeny Induction activation of lysogenic prophage followed by viral replication and cell lysis Causes of Induction UV light/chemicals/environmental cues Lysogeny results in... - the spread of the virus without killing the host cell - thought to be a less deadly form of parisitism Transduction: Impact of lysogeny - The phage increases genetic diversity in bacteria by transporting genes from one bacterium to another 2nd Mechanism allows bacteria to acquire new genes = new proteins Indirect transmission via a _________ can occur since virus can remain viable on surfaces for about 3 days fomite Viral particles have been found in ______ __________ but there is no evidence for fecal-oral transmission. fecal samples + ss RNA virus viral genome looks like mRNA and codes for a protein; many already have 5' methylguanine cap and Poly A tail - ss RNA virus needs to take the time to make complementary RNA Virus Shapes filamentous, icosahedral, enveloped, complex Flexible filamentous ex: ebola Rigid filamentous ex: tubulovirus Icosahedral ex: actenovirus Enveloped ex: Herpes - steals the envelope from the host membrane Complex ex: T2 bacteriophage - head and tail COVID - enveloped virus - +ss mRMA - spike proteins that are species and tissue specific Covid 19 genome codes for ____ nonstructural proteins that are involved in ______ ____________, ____________, and ___________. 16 viral replication maturation release Portals of Entry - nasal and oral passages - conjunctiva of the eyes S-proteins on viral envelope bind to... - angiotensin-converting enzyme 2 (ACE2) on host cells - which triggers either viral endocytosis or membrane fusion and mRNA entry ACE2 proteins present in many tissues like... lungs, kidneys, heart, arteries, GI tract