1. Based on your understanding of the chapter material and the information in th
ID: 151271 • Letter: 1
Question
1. Based on your understanding of the chapter material and the information in the passage, which of the following best defines something as a virus? Are virophages a type of virus or something different?
f. It must have a capsid and single-stranded nucleic acid. Virophages are therefore not a type of virus.
2. The introductory passage discusses the way that virophages interfere with the ability of megaviruses to reproduce and the possible selective benefits of this. However, there are many ways that cells attempt to survive attacks by viruses. According to the chapter, what is another way that cells have evolved to avoid viral infection?
d. The host develops enzymes that cleave the restriction endonucleases of the virus.
a. It must have a capsid and double-stranded or single-stranded DNA. Virophages are therefore a type of virus. b. It must have a capsid and a linear nucleic acid that encodes replication enzymes. Virophages are therefore not a type of virus. c. It must have an envelope, capsid, and nucleic acid, which can be double-stranded or single-stranded, and DNA or RNA. Virophages are therefore not a type of virus. d. It must have a capsid and linear nucleic acid. Virophages are therefore a type of virus. e. It must have a capsid and a nucleic acid, which can be double-stranded or single-stranded, circular or linear, and DNA or RNA. Virophages are therefore a type of virus.f. It must have a capsid and single-stranded nucleic acid. Virophages are therefore not a type of virus.
2. The introductory passage discusses the way that virophages interfere with the ability of megaviruses to reproduce and the possible selective benefits of this. However, there are many ways that cells attempt to survive attacks by viruses. According to the chapter, what is another way that cells have evolved to avoid viral infection?
a. An attachment receptor on the host cell surface that is recognized by the virus is mutated. b. A mutation in the host blocks translation at the ribosome. c. Cells undergo a phenomenon called circular permutation, in which the same set of genes is arranged differently in each individual.d. The host develops enzymes that cleave the restriction endonucleases of the virus.
Explanation / Answer
1. The correct choice is e.
Viruses are nucleoprotein entities. They are simple in structure consisting a core of nucleic acid either DNA or RNA (never both) surrounded by a protein coat also called as capsid. Virus may contain a double stranded DNA like in Adenovirus which is mostly linear or Papova virus which has circular DNA. Parvoviruses consist of single stranded DNA. Rabies virus, Influenza virus are single stranded RNA viruses whereas Rotavirus is a double stranded RNA virus. Envelope may not be present in all viruses but can be seen in some like Mumps virus or Lipovirus. Viruses depend on the host cell for their replication as the proteins and enzymes used are of host cell itself. Thus, Virus must have a capsid and a nucleic acid, which can be double-stranded or single-stranded, circular or linear, and DNA or RNA. Virophages are small double stranded DNA viruses which infect other giant viruses.
2. The correct choice is a.
Viruses attach to a specific receptor site present on the host cell membrane. This is acheived by the attachment of proteins in the capsid or when envelope is present then through glycoproteins embedded in viral envelope. This attachment is very specific like lock and key model. The specificity of this interaction determines that which host and the cells within the host can be infected by a particular virus. Thus when this attachment receptor is mutated the host cells can avoid viral infection.
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