Virus Genome and Structure Quiz
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Questions and Answers

What percentage of amino acid residues in the HIV-1 nucleocapsid protein are basic?

  • 25 per cent
  • 40 per cent
  • 33 per cent
  • 29 per cent (correct)
  • What is the primary function of a virion?

  • To protect and deliver the virus genome (correct)
  • To promote virus replication in host cells
  • To aid in the synthesis of viral proteins
  • To regulate immune responses in the host
  • What types of nucleic acid can a virus genome consist of?

  • Either RNA or DNA molecules (correct)
  • Only RNA molecules
  • Protein and lipid combinations
  • Only DNA molecules
  • Which feature is characteristic of the HIV-1 nucleocapsid protein?

    <p>It has two zinc fingers.</p> Signup and view all the answers

    Which type of viruses predominantly have segmented genomes?

    <p>ssRNA viruses</p> Signup and view all the answers

    Which enzyme would be used to determine if a virus has RNA as its genome?

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

    Which of the following is a bond that forms specifically in ssRNA?

    <p>G–U bonds</p> Signup and view all the answers

    In which type of virus is the genome typically packaged in one virion?

    <p>Influenza viruses</p> Signup and view all the answers

    How many categories of virus genomes are there based on nucleic acid type and strand configuration?

    <p>Four categories</p> Signup and view all the answers

    What component do many viruses have that aids in the entry into host cells?

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

    Which of the following viruses has a segmented genome?

    <p>Influenza viruses</p> Signup and view all the answers

    What is a potential disadvantage of segmented genomes in viruses with segments packaged in separate virions?

    <p>New cells may become infected only if all genome segments enter the cell.</p> Signup and view all the answers

    What form is often seen in regions of secondary structure in single-stranded nucleic acids?

    <p>Stem-loops</p> Signup and view all the answers

    What is the role of the internal ribosome entry site in poliovirus RNA?

    <p>Binds cellular proteins to initiate translation</p> Signup and view all the answers

    What structure is primarily responsible for packaging the virus genome?

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

    How do tertiary structures of nucleic acids impact virus replication?

    <p>They facilitate molecular interactions.</p> Signup and view all the answers

    Which of the following is not a category of virus genome?

    <p>Mixed-strand RNA</p> Signup and view all the answers

    What additional information does a virus genome carry beyond encoding virus proteins?

    <p>Signals for gene expression control</p> Signup and view all the answers

    What is a characteristic structure that can form due to intramolecular base pairing in ssRNA?

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

    What is one benefit of having a segmented genome for a virus?

    <p>Possibility of new gene combinations.</p> Signup and view all the answers

    What distinguishes a double-stranded RNA virus from other types?

    <p>It consists of two RNA strands</p> Signup and view all the answers

    What is the length of the largest RNA genomes known, specifically those of coronaviruses?

    <p>33 kb</p> Signup and view all the answers

    Which characteristic is not associated with the nucleic-acid-binding proteins mentioned?

    <p>High molecular weight</p> Signup and view all the answers

    What type of bonding occurs in single-stranded DNA (ssDNA)?

    <p>G–C and A–T bonding</p> Signup and view all the answers

    Study Notes

    Virus Genome Size

    • The largest known RNA genomes are those of some coronaviruses, which are 33 kb of ssRNA
    • Some viruses, such as the mimivirus, have larger genomes than the genomes of some simple cellular organisms
    • The smallest genomes of cellular organisms include some mycoplasmas

    Secondary and Tertiary Structure

    • The viral genome stores additional information beyond just the genes to be expressed
    • This information may be contained in the nucleotide sequences, or in the structures created by intramolecular base pairing in single-stranded genomes
    • Secondary structures are formed by intramolecular base pairing, which results in regions like stemloops and bulges
    • Tertiary structures are formed when regions of secondary structure in single-stranded nucleic acids fold into specific shapes
    • Many of these tertiary structures are important in molecular interactions during virus replication, such as the 5' end of poliovirus RNA, which contains an internal ribosome entry site for binding of proteins to initiate translation
    • Most proteins associated with virus genomes are virus-coded, such as the HIV-1 nucleocapsid protein, which coats the virus RNA.

    Protein Characteristics

    • Besides being basic, nucleic-acid-binding proteins may contain other characteristics, like zinc fingers
    • In some viruses, such as tobacco mosaic virus, the protein coating the genome constitutes the capsid of the virion

    Segmented Genomes

    • Most virus genomes consist of a single molecule of nucleic acid
    • Some viruses have segmented genomes, where their genes are encoded in two or more nucleic acid molecules
    • Segmented genomes are more common among RNA viruses than DNA viruses
    • Examples of RNA viruses with segmented genomes include the influenza viruses, which package their segments in one virion, and brome mosaic virus, which packages the segments in separate virions
    • Most dsRNA viruses, such as members of the family Reoviridae, have segmented genomes
    • Segmented genomes provide the potential for new gene combinations and rapid evolution, but require that all genome segments enter a cell for infection to occur

    Virus Structure

    • Outside of a host cell, viruses survive as virus particles, also known as virions
    • Virions act as gene delivery systems, protecting the viral genome and aiding its entry into a host cell
    • The viral genome is packaged within a protein structure called a capsid
    • Many viruses also have a lipid component, forming an envelope, which typically contains proteins that aid entry into host cells
    • Some viruses form protective protein occlusion bodies around their virions

    Virus Genome Composition

    • Every virion contains the virus genome in the form of one or more molecules of nucleic acid
    • For any one virus, the genome is composed of either RNA or DNA
    • If a new virus is isolated, its susceptibility to a ribonuclease and a deoxyribonuclease can be tested to determine if it is an RNA or DNA virus
    • Each nucleic acid molecule is either single-stranded (ss) or double-stranded (ds), yielding four categories of virus genome: dsDNA, ssDNA, dsRNA, ssRNA

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    Description

    Test your knowledge about virus genomes, focusing on RNA sizes and structural formations. This quiz covers topics like the largest RNA genomes, secondary and tertiary structures, and their roles in virus replication. Delve into the fascinating world of viral genetics and its complexities.

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