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8/3/2019 CLasses of Viruses and Synthesis of Viral Nucleic Acids 15
http://slidepdf.com/reader/full/classes-of-viruses-and-synthesis-of-viral-nucleic-acids-15 1/7
8/3/2019 CLasses of Viruses and Synthesis of Viral Nucleic Acids 15
http://slidepdf.com/reader/full/classes-of-viruses-and-synthesis-of-viral-nucleic-acids-15 2/7
SS DNA Virusinfecting host cell
Host DNA dependent DNApolymerase use ssDNA tosynthesize complementarystrand. The original ssDNAstrand may be self priming(with a hairpin structure atone end) or a primer molecule can be brought infrom the capsid. Theresulting dsDNA will then beused as template for mRNAand DNA synthesis usinghost coded DNA Dependentpolymerase enzymes
Host DNA dependentDNA Polymerase
Host DNA dependentRNA polymerase
Viralparticle
CLASS II Viruses ± ssDNA
Host DNA
Viral ssDNA injectedinto cell- used astemplate by host DNA
polymerase tosynthesize dsDNA.
SynthesizeddsDNA. Thisserves astemplate for both mRNAand further
DNAsynthesis.
mRNA (plus ss RNA). mRNA willbe translated to viral proteinsincluding viral enzymes andcapsid
Progeny viral ssDNAresulting fromdegradation of one strandof dsDNA by viralnuclease enzyme
dsDNA
8/3/2019 CLasses of Viruses and Synthesis of Viral Nucleic Acids 15
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dsRNA Virusinfecting host cell
V iral RNA dependent RNApolymerase synthesizes (+)ssRNA which is mRNA thatis translated to viral codedproteins. Progeny dsRNA isalso synthesized by RNAdependent RNA polymerase.
Viralparticle
CLASS III Viruses ± dsRNA
Host DNA
(+) ssRNA (mRNA). This stand will be synthesized by the viral RNA dependent RNA polymerase using the minus (-) strand as template.This newly synthesized strand will serve as mRNA and will be translated to viral proteins including viral enzymes that will allow theinfection process to continue. [Note that dsRNA cannot serve as mRNA,. Hence viral RNA dependent RNA polymerase cannot besynthesized directly from the injected dsRNA and must be brought in the capsid. ssRNA (+) is first synthesized and then be translated to
proteins including RNA dependent RNA polymerases and other enzymes/structural components required by the virus.
RNAdependentRNApolymerase
Viral dsRNA
dsRNA(Progenynucleic acid
that will beassembledwith thecapsid.)
tra
nslation
8/3/2019 CLasses of Viruses and Synthesis of Viral Nucleic Acids 15
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(+) ssRNA Virusinfecting host cell
(+) ssRNA is first translatedto produce viral codedproteins including RNAdependent RNA polymerase.This enzyme can then beused to synthesize more (+)strands which will serve asboth mRNA and progenyvirus.
Viralparticle
CLASS IV Viruses ± (+) ssRNA
Host DNA
Viral (+)ssRNA.Functionsas mRNA
Synthesized(-) ssRNA translation
(+) ssRNAsynthesized by viralcoded RNAdependent RNApolymerase using (-)strand as template.This can serve asboth mRNA andprogeny virus
Viral coded RNA dependent RNA polymerase synthesizedin host cell since the introduced (+) ssRNA can servedirectly as mRNA
8/3/2019 CLasses of Viruses and Synthesis of Viral Nucleic Acids 15
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(-) ssRNA Virusinfecting host cell
(-) ssRNA is transcribed to(+) ssRNA by polymerasebrought by the virus. (+)ssRNA serves as mRNA andalso serves as the templatefor the synthesis of progenyviral nucleic acid (-) ssRNA.
Viralparticle
CLASS V Viruses ± (-)ss RNA
Host DNA
(+) ssRNA (mRNA). This stand will be synthesized using the minus (-) strand as template by the viral RNA dependent RNA polymerasebrought in the capsid. This newly synthesized strand will serve as mRNA and will be translated to viral proteins including viral enzymesthat will allow the infection process to continue. Note the since the (-) ssRNA cannot serve as mRNA, viral coded proteins such as RNAdependent RNA polymerases cannot be synthesized. Hence this enzyme is brought to the cell in the capsid of the infecting virus and allowfor the synthesis of viral coded proteins required for infection to proceed.
RNAdependentRNApolymerase
Viral (-)ssRNA
(-) ssRNAsynthesizedusing the (+)
strand astemplate.This (-)strand is theprogenynucleic acidthat will beassembledwith the
capsid.
transla
tion
8/3/2019 CLasses of Viruses and Synthesis of Viral Nucleic Acids 15
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(+)ssRNA Retrovirus infecting hostcell
(+) ssRNA is reversetranscribed to dsDNA whichis then integrated into thechromosome. Transcriptionthen takes place resulting in(+) ssRNA that serves asmRNA as well as progenyvirus nucleic acid.
Viralparticle
CLASS VI Viruses ± retro viruses (+)ssRNA
Host DNA
Viral (+)ssRNA
(+) ssRNA
Protease
Integrase
Reverse transcriptase
RNAse
Host DNA dependentRNA polymerase
Synthesis of ssDNA byreverse
transcriptase.ThecomplementaryDNA strand isthensynthesizedto give dsDNA
Integration of dsDNA by integrase
Synthesis of (+) ssRNA byhost coded polymerasewhich serves as mRNA aswell as progeny viralnucleic acid
8/3/2019 CLasses of Viruses and Synthesis of Viral Nucleic Acids 15
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Class VII dsDNAvirus infecting hostcell
Ds DNA is transcribed to(+)ssRNA (mRNA) which isthen used as template byreverse transcriptase tosynthesize progeny nucleicacid.
Viralparticle
CLASS VII Viruses ± dsDNA viruses thatreplicate using RNA intermediate
Host DNA
ViraldsDNA
Host DNA dependentRNA polymerasedsDNA
translation
Translation of viralcoded proteins suchas reversetranscriptase and
capsids
Synthesis of ssDNA by reversetranscriotase.Complementary
strand is thensynthesized to givedsDNA (progenyviral nucleic acid)
(+) ssRNA
Synthesis of (+) ssRNA(mRNA) byhost
polymerase