Virus Genome Replication Overview
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Questions and Answers

What is the primary difference in the number of proteins involved in bacterial versus eukaryotic DNA synthesis systems?

  • Eukaryotic systems involve fewer proteins.
  • Bacterial systems involve more proteins.
  • Both systems involve the same number of proteins.
  • Bacterial systems involve fewer proteins. (correct)

    • How is the Okazaki fragment synthesized during DNA replication?

  • Continuously on the leading strand.
  • Discontinuously on the lagging strand. (correct)
  • Using only one type of DNA polymerase.
  • In a single step with helicase.

    • Which mode of replication is also known as a rolling circle mode?

  • Semiconservative replication
  • Sigma mode (correct)
  • Theta mode
  • Conservative replication

    • In which type of replication do the daughter molecules each contain a strand of the original DNA?

    <p>Semiconservative replication</p> Signup and view all the answers

    What are concatemers in the context of viral DNA replication?

    <p>Very large DNA molecules composed of multiple copies of the virus genome.</p> Signup and view all the answers

    What are the two modes of replication for circular DNA genomes?

    <p>Theta and sigma modes</p> Signup and view all the answers

    Which type of virus uses cell primase to synthesize RNA primers during its replication cycle?

    <p>Polyomaviruses</p> Signup and view all the answers

    What does the process of circularizing a linear DNA molecule mean?

    <p>Joining the ends to form a closed loop.</p> Signup and view all the answers

    What role does the 3 –OH group in a polypurine tract play in retrovirus replication?

    <p>It primes (+) DNA synthesis.</p> Signup and view all the answers

    Which polymerase is required by a DNA virus for genome replication?

    <p>DNA-dependent DNA polymerase</p> Signup and view all the answers

    Which type of replication may occur early and late in the infection cycle of some DNA viruses?

    <p>Both theta and sigma modes</p> Signup and view all the answers

    Which class of viruses uses protein primers for nucleic acid replication?

    <p>Some animal viruses and phages</p> Signup and view all the answers

    During latency, how is viral DNA treated during cell division?

    <p>It gets incorporated and copied.</p> Signup and view all the answers

    What type of primer is used by hepadnaviruses to initiate (−) DNA synthesis?

    <p>Protein primer</p> Signup and view all the answers

    What happens to the protein primers used by some viruses after their role is complete?

    <p>They remain linked to the genome.</p> Signup and view all the answers

    Which polymerase do some viruses rely on from a host cell for genome replication?

    <p>Both DNA and RNA polymerases</p> Signup and view all the answers

    What is the primary purpose of virus genome replication?

    <p>To provide copies of the genome for progeny virions</p> Signup and view all the answers

    How do DNA viruses typically replicate their genomes?

    <p>Directly to DNA</p> Signup and view all the answers

    What do plus-strand genomes have in common with the virus mRNA?

    <p>They have the same sequence</p> Signup and view all the answers

    Which class of viruses replicates their (+) RNA genomes via a (−) RNA intermediate?

    <p>Class IV</p> Signup and view all the answers

    What is the characteristic process of Class VII viruses?

    <p>Reverse transcription from RNA to DNA</p> Signup and view all the answers

    What is the significance of single-stranded DNA in virus replication?

    <p>It is converted to double-stranded DNA prior to copying</p> Signup and view all the answers

    What is the relationship between single-stranded genomes and their mRNA counterparts?

    <p>One is complementary to the other</p> Signup and view all the answers

    Which of the following statements about RNA viruses is false?

    <p>All RNA viruses replicate through reverse transcription</p> Signup and view all the answers

    What role does an endonuclease play during virion assembly?

    <p>It cuts a genome length from a concatemer.</p> Signup and view all the answers

    Which mechanism do some dsRNA viruses use for genome replication?

    <p>Both conservative and semi-conservative mechanisms.</p> Signup and view all the answers

    What is required for the synthesis of RNA molecules in ssRNA viruses?

    <p>RNA-dependent RNA polymerase.</p> Signup and view all the answers

    Where are the genomes of most DNA viruses replicated?

    <p>In the nucleus</p> Signup and view all the answers

    What is a notable characteristic of class IV viruses of eukaryotes?

    <p>They replicate RNA in association with cytoplasmic membranes.</p> Signup and view all the answers

    In the replication process of dsRNA viruses, which enzyme is involved in unwinding the RNA?

    <p>Helicase.</p> Signup and view all the answers

    Which of the following virus genomes is replicated solely in the cytoplasm?

    <p>dsRNA</p> Signup and view all the answers

    What is unique about the replication of retroviruses?

    <p>They convert RNA to DNA in the cytoplasm.</p> Signup and view all the answers

    What is the outcome in terms of strands during the semi-conservative replication of dsRNA?

    <p>Each progeny molecule consists of one parental and one daughter strand.</p> Signup and view all the answers

    Which type of virus genome is replicated in the nucleus when segmented?

    <p>(-) RNA (segmented genome)</p> Signup and view all the answers

    Where do many groups of viruses, including picornaviruses, derive their membranes from?

    <p>The endoplasmic reticulum.</p> Signup and view all the answers

    Where must both plus- and minus-strand RNA have a binding site for RNA-dependent RNA polymerase?

    <p>At the 3' end.</p> Signup and view all the answers

    All ssDNA virus genomes are replicated in which location?

    <p>Nucleus</p> Signup and view all the answers

    Which of the following statements is correct regarding dsDNA viruses?

    <p>Some dsDNA viruses replicate in the nucleus.</p> Signup and view all the answers

    In which of the following locations do most RNA viruses replicate?

    <p>In the cytoplasm</p> Signup and view all the answers

    Which virus type has a unique replication process involving the conversion of RNA to DNA in the cytoplasm and DNA to RNA in the nucleus?

    <p>Retroviruses</p> Signup and view all the answers

    What initiates the replication of many RNA viruses?

    <p>The first nucleotide base pair with a nucleotide in the viral RNA</p> Signup and view all the answers

    Which reaction occurs first during the initiation of replication?

    <p>Recognition of the initiation sequence by proteins</p> Signup and view all the answers

    What is required for the initiation of many DNA genomes replication?

    <p>An RNA or protein primer</p> Signup and view all the answers

    How do ssDNA viruses such as parvoviruses initiate replication?

    <p>By self-priming at the 3' end</p> Signup and view all the answers

    In the replication of cell DNA, what is synthesized after the double helix is unwound?

    <p>Short sequences of RNA</p> Signup and view all the answers

    What is the role of the 3' –OH group during the initiation of DNA replication?

    <p>It forms a linkage with the first nucleotide</p> Signup and view all the answers

    Which of the following statements about RNA primers is true?

    <p>Only one RNA primer is needed for the entire leading strand</p> Signup and view all the answers

    How many primers are typically required for the Okazaki fragments during DNA replication?

    <p>Several, as multiple primers are synthesized</p> Signup and view all the answers

    Study Notes

    Virus Genome Replication

    • Virus genome replication is the fifth step in the generalized replication cycle
    • The infecting virus's genome is replicated to amplify viral transcription and produce progeny virions' genomes
    • DNA viruses replicate their genomes directly into DNA, while RNA viruses replicate their genomes directly into RNA
    • Some DNA viruses replicate via RNA intermediates, and some RNA viruses replicate via DNA intermediates
    • Replication modes of virus genomes are summarized in Figure 7.1

    Single-Stranded Genomes

    • Single-stranded genomes are designated as + or -, based on their relationship to the virus's mRNA
      • strand genomes have the same sequence as the mRNA (except in DNA where thymine replaces uracil)
      • strand genomes have a sequence complementary to the mRNA (except in DNA where thymine replaces uracil)
    • Single-stranded DNA is converted into double-stranded DNA before copying

    Replication in Eukaryotic Cells

    • Virus genomes are delivered to the cytoplasm or nucleus
    • The location of replication varies based on the genome type (see Table 7.1)
    • Most DNA viruses replicate in the nucleus
    • Some double-stranded DNA viruses replicate in the cytoplasm
    • Most RNA viruses replicate in the cytoplasm
    • Minus-strand RNA viruses with segmented genomes replicate in the nucleus
    • Retroviruses and pararetroviruses produce DNA from RNA in the cytoplasm and RNA from DNA in the nucleus

    Initiation of Genome Replication

    • Each virus genome has a specific sequence where replication starts, recognized by initiation proteins
    • Replication requires priming, the first reaction of a nucleotide with an -OH group at the initiation site
    • RNA viruses (e.g., rotaviruses, rhabdoviruses) initiate with the first nucleotide base-pairing with a nucleotide in the viral RNA
    • This initial nucleotide acts as a primer for RNA replication
    • Some single-stranded DNA viruses (like parvoviruses) use self-priming, using complementary regions at the 3' end of the DNA

    RNA and Protein Primers

    • DNA synthesis starts after a helicase unwinds a region of the double helix
    • A primase synthesizes short RNA sequences that are complementary to DNA regions
    • These RNAs (primers) are required for initiating the leading strand synthesis
    • Multiple primers are required for Okazaki fragments in the lagging strand
    • The 3'-OH group of the primer RNA is linked to the first nucleotide of the new DNA sequence

    Polymerases

    • Viruses use DNA or RNA polymerases for genome replication
    • Some viruses encode their own polymerases, while others utilize host cell enzymes
    • DNA viruses requiring DNA-dependent DNA polymerisation
    • Viruses with small genomes often use a cell's enzyme, while viruses with large genomes typically encode their own
    • RNA viruses require RNA-dependent RNA polymerase as the replicase enzyme
    • Retroviruses utilize a reverse transcriptase to convert RNA into DNA

    DNA Replication

    • DNA viruses in Class I and II replicate their genome via dsDNA
    • Single-stranded DNA viruses first synthesize a complementary strand to form dsDNA
    • Replication initiates at specific DNA sequences called origins of replication
    • Proteins involved in DNA replication include helicases, single-stranded DNA binding proteins, and DNA polymerases

    Double-Stranded RNA Replication

    • Double-stranded RNA (dsRNA) genomes need to be unwound by a helicase prior to replication
    • Some dsRNA viruses replicate via a semi-conservative mechanism, similar to dsDNA
    • Other dsRNA viruses use a conservative mechanism of replication
    • (Figure 7.6) illustrates the conservative mechanism

    Single-Stranded RNA Replication

    • Single-stranded RNA (ssRNA) replication in Classes IV and V involves the synthesis of complementary RNA strands, using the original strand as a template
    • RNA-dependent RNA polymerase is recruited to the 3' end of the template
    • Both + and - strand RNAs have a binding site for the polymerase at their 3' ends

    Reverse Transcription

    • Some RNA viruses use a DNA intermediate in their replication, while some DNA viruses utilize an RNA intermediate
    • Reverse transcription involves two major steps: converting (+) RNA into (-) DNA, and synthesizing a second DNA strand
    • This process is catalyzed by a reverse transcriptase, an enzyme encoded by the virus
    • Reverse transcription takes place inside the infected cell's viral structure

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    Virus Genome Replication PDF

    Description

    Explore the intricate process of virus genome replication, the essential fifth step in the viral replication cycle. This quiz covers the distinctions between DNA and RNA viruses, single-stranded genome classifications, and replication mechanics in eukaryotic cells. Test your understanding of viral genome amplification and transcription methods.

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