6. Infectious particle (virus) Flashcards

Question

ANIMAL VIRUSES: DNA genome - example? - where is DNA replication? - what is penetration? - host transcription/translation apparatus synthesizes which proteins at which stage ish - assembly (of proteins) occurs where? is there an envelope? - ssDNA genome first converted to WHAT?

Answer 1

- Herpesvirus - in nucleus of animal cell! - PENETRATION: fusion of cell cytoplasmic membrane with virus envelope --> Nucleocapsid is transported to nucleus where viral DNA is uncoated. Host transcription/translation apparatus synthetizes: a) Immediate early proteins (transcription factors and, in some cases, virus-specific RNA polymerase). b) Delayed early proteins (viral-specific DNA polymerase, and other viral proteins necessary for replication. c) Late proteins: nucleocapsid - Assembly occurs in the nucleus --> envelope is added via a budding process through inner membrane of the nucleus. *The complete virions are then secreted out of the cell by the ER-Golgi pathway. - ssDNA genome: first converted to a dsDNA replicative form.

Answer 2

- poliovirus, hepatitis A virus, Sars-Cov 2 - genome can be translated directly! - in poliovirus: + strand RNA serves as a template for synthesis of a large polyprotein that is cleaved into proteins (structural components like structural coat proteins, proteases and RNA replicase) - +strand DNA can also be used to synthesize a minus strand (using RNA dependent RNA polymerases) + convert minus strand back to positive strand using the same enzyme

Answer 3

no! DNA produces +gRNA --> replicated/transcripted to smaller pieces of RNA that are then translated

Answer 4

- Measles, rabies (rhabdovirus), influenza (orthomyxovirus) - genome CANNOT be translated directly. The RNA genome (minus- strand) is first transcribed into a plus- strand RNA by an RNA-dependent RNA polymerase carried inside the virions. - nothing! needs to inject DNA AND RNA-dependent RNA polymerase inside host cell

Answer 5

Rotavirus (Reovirus). - The dsRNA genome CAN NOT be translated. First, a plus-strand RNA must be synthetized by a viral-encoded RNA-dependent RNA polymerase using the minus strand as the template. - The plus-strand is then translated into proteins and is used as a template to synthesize a minus strand to yield dsRNA genomes. (double strand = bit more protected)

Answer 6

- ss RNA genome - HIV. - virion carries two identical copies of the genome (plus-strand ssRNA), reverse transcriptase, integrase and proteases. *the reverse transcriptase is an RNA- dependent DNA polymerase that reverse transcribes the RNA genome into DNA. *The DNA genome travels to the nucleus and is integrated into the host DNA. - envelopped! - LTR: long terminal repeats (at end of ssRNA). Contain promoters for transcription and participate in the integration process. - PROVIRUS: integrated viral DNA. Contrary to the lambda prophage, the provirus cannot excise from the host genome.

Answer 7

depends on what the genome is! DNA: *has to enter nucleus! transcribed in nucleus! 1) dsDNA (+) --> transcription of minus strand into mRNA --> makes protein of virus 2) ssDNA (+) --> synthesis of double strand (dsDNA intermediate) --> transcription of minus strand into mRNA --> makes protein of virus RNA: 3) dsRNA (+) --> transcription of minus strand into mRNA --> makes protein of virus 4) ssRNA (+) --> used directly as mRNA! (translated right away by host) 5) ssRNA (-) --> transcription of minus strand into positive strand mRNA 6) ssRNA (+) retrovirus! --> reverse transcription into dsDNA intermediate --> integrates in DNA of eukaryote OR transcription of minus strand into mRNA

Answer 8

BACTERIA: - bacteria lyses/exploses and dies ANIMAL cells (multicellular orgs) 1) death of cell and release of virus --> lysis 2) transformation into tumor cell --> tumor cell division --> transformation 3) attachment and penetration --> cell fusion 4) slow release of virus without cell death/virus present but not replicating --> latent/persistent infection

Answer 9

1) LYSIS - destruction of tissues and organs --> can make your organ non-functional and you die - can also leave scars --> changes structure of organ 2) TRANSFORMATION - forms tumor cell --> cell acquires immortality, characterized by uncontrolled replication 3) CELL FUSION - enveloped viruses that fuse with host cell cytoplasmic membrane carries viral proteins that fuse biological membranes --> cell fusion results in hybrid cells (2 cells fused together with a fused nucleus) that have chromosomal aberrations (ie sometimes twice # of chromosomes) and are usually weird/affect performance of cells/ short-lived 4) LATENT/PERSISTENT INFECTION - cell doesnt carry out function very well - may revert to lytic infection

Answer 10

- yes! DNA: Epstein-Barr virus (mononucleose) and Human Papillomavirus (cause cervix cancer) RNA: Hepatitis C virus, Hepatitis C virus (cause liver cancer) and human T-lymphotrophic virus type 1 (retrovirus) - 15-20% 1) transduction 2) insertion of a strong promoter 3) inactivation of a tumor suppressor gene 4) expression of a viral protein that induces transformation (DNA virus! Epstein Barr or Human papillovirus) IMPORTANT ONE FOR THE CLASS

Answer 11

- DNA virus! - does NOT have a cell counterpart - integration of viral genome into host genome may occur (ie adenovirus) OR viral genome may persist in cell as an extrachromosomal episome 1) where 2 sheets of epithelium meet, there's a "hole" where the virus can come in and reach base layer (cells that are actively replicating) 2) virus infects base layer cells --> episome in host cell --> normal replication of virus = spread of virus + get greedy and make E6 and E7 (?) --> create virus protein + actively replicate, but then die (purple cells) 3) 1 in a million chance --> DNA of virus recombines into nucleus --> then replication of virus stops BUT E6 and E7 are still expressed --> so red cells divide like crazy and cause cancer!!! *slide: Some DNA viruses that cause tumors do so because they have infected a nonpermissive host, in which they cannot complete their infection cycle. The cell is infected and undergoes uncontrolled replication. Because the virus cannot complete its replication, the cells will never die.

Answer 12

yes! HPV vaccine - very useful! decreased infection rate to <1% in 2018 - for both! females get the cervix cancer but males can give it to females

Answer 13

- Most antiviral drugs also target host structures, resulting in toxicity (viruses use host cell machinery). Risk to the host may NOT justify the use of antiviral. --> ie not worth it for flu bc antiviral might kill you (and the flu won't) - Antibiotics are ineffective. 1) nucleoside analogs - most successful and commonly used antivirals - (e.g., AZT, Acyclovir, Malnupiravir): block reverse transcriptase and production of viral DNA (RNA viruses) (ie block RNA dependent RNA polymerase) 2) Protease inhibitors inhibit the processing of large viral proteins into individual components (e.g. Paxlovid). 3) Fusion inhibitors prevent viruses from successfully fusing with the host cell.