Chapter 13: Viruses Flashcards
structure of viruses
outside: protein coat (capsid)
interior: genome and proteins (includes DNA or RNA)
capsids
protein coats that enclose and protect genetrial material (DNA or RNA)
have lipid covering
made from identical subunits called capsomeres
virsues classified into several morphological types: (4)
1) helical- long rods, cylindral capsid, flexible (ex. rabies, ebola)
2) polyhedral- animal, plant, bacteria viruses , 20 triiangular faces and 12 corners (ex. adenovirus, poliovirus)
3) complex- complciated strutures, capsid- polyhedral, tail- helical (ex. bacteriophage)
4) enveloped- envelope composed of lipids, proteins, and carbs. May be covered by spikes (glycoproteins) for atachment (ex. SARS coronoca virus, influenza virus, herpes)
naked viruses
no coat (lipid) outside the capsid ex. rhinovirus (common cold) polio, norwalk
for a virus to multiply it must:
1) invade the host cell
2) must take over hte host’s metabolic machinery
(one step growth curve)
steps in multiplication of bacterial virus (6)
1) attachment
2) penetration
3) transcribation
4) biosynthesis
5) maturation
6) lysis
lytic cycle
-phage attaches to host cell and injects DNA
-phage DNA ciculizes and enters lytic/lysogenic cycle
-new DNA and proteins are assembled
-cell lyses, releasing phage virions
lysogeny cycle
-phage injects DNA
-DNA circulaes and enters lysogenic/ lytic cycle
-DNA integrates within the bacterial chromosome by recombincation becoming a prophage
-bacterium reproduces normally
-many cell divisions
-prophage may initiation a lytic cycle
steps in multiplication of animal viruses (6)
1) attachment: use of spikes to cell membrane
2) entry: endocytosis or fusion
3) uncoating: requires viral/ host enzymes to release genetic material
4) biosynthesis: DNA/ RNA / protein synthesis and multiplication
5) maturation: involves packaging nucleic acid into protein coat
6) release: can involve budding (enveloped viruses) / rapture nin-enveloped) of the host cells
viral genome multiplication steps
1) replication: DNA duplicates (DNA polymerase)
2) transcription: RNA synthesis (RNA polymerase)- uses DNA template and then to RNA
3) translation: protein synthesis, ribosome reads strand to create protein
DNA viruses
-dsDNA: double stranded, replicate in host nucleus, synthesis like the host (ex. herpes, vericella-zoster, epstein-barr, smallpox, adenovirus)
-ssDNA: single-stranded, replicates in host nucleus (ex. parvovirus)
RNA viruses
-ssRNA (-): single-stranded antisense, RNA polymerase used to convert negative strands to postive to make more viral proteins. virons assemble in the cytoplasm (ex. measles , influenza, ebola)
-ssRNA (+): single-stranded, RNA used by host ribosomes to make viral proteins. RNA polymerase converts positive to negative to postive virions assembled in the cytoplasm (SARS corona virus, rhinovirus, polio)
-Ds RNA: double stranded RNA. used to make viral proteins (ex rotavirus)
-Retroviruses: uses reverse transcriptases to convert ssRNA to DNA - HIV-1 (AIDs)
cancer
genetic material of viruses become integrated into the host cell’s DNA
10% caused by viruses
viruses activatate oncogens (part of the cellular genome)
activated oncogenes transform normal cells into cancerous cells which have increased gorwth and loss of contact inhibition
virus specfic antigens are found in the nucleus
oncogenic DNA viruses
-adenoviriade
-herpes virus
-papillomavirus
-hep B virus
acute infection
sudden onset
ex. influenza
