Chapter 6 Interactive Assignment

Viral Genome

-less than 3000 genes -may be negative sense RNA -may be single stranded -may be RNA -may be DNA -may be positive sense RNA

Cellular Genome

-more than 3000 genes -always DNA -always double stranded

Viruses are inactive macromolecules inside of a host cell. True or False

False Viruses are merely inactive macromolecules outside of a host cell. However, inside of a host cell, they can take over the cellular machinery for replication.

______________ is a naturally-occurring protein that signals cells when a virus is present thereby stimulating the production of ______________________. This process can be enhanced when interferon is prescribed therapeutically in patients infected with the hepatitis B virus, for example.

Interferon antiviral proteins

Place the steps in the correct order to assess your understanding of lytic infections exhibited by bacteriophage.

Lysogenic Cycle -phage DNA becomes a prophage -phage DNA is replicated as host cell replicates Lytic Cycle 1. Adsorption 2. Penetration 3. Duplication of phage components; replication of virus genetic material 4. Assembly of new virions 5. Maturation 6. Lysis of weakened cell

Of all infectious agents, which group has the most variety of drugs designed to treat infections? a. Bacteria b. Helminths c. Viruses d. Protozoans e. Fungi

a. Bacteria Because bacteria differ significantly from human eukaryotic cells, it is easiest to design antimicrobials that target this group without causing damage to human host cells. The other infectious agents are either eukaryotic (meaning they have similar cellular structures to human cells) or intracellular agents.

Antibiotics would be effective against which of these infections? (NOTE: Please change all question marks to checkmarks for correct answers or empty boxes for incorrect answers.) a. Cholera b. Cold sores c. Whooping cough d. Chickenpox e. Genital warts f. Syphilis

a. Cholera c. Whooping cough f. Syphilis Cholera, whooping cough, and syphilis are caused by bacteria. The others are viral agents, and antibiotics would not be effective against these noncellular agents.

Select characteristics exhibited by viral capsids. Check all that apply. a. Composed entirely of protein b. May be an icosahedral shape c. Contain a significant amount of phospholipid d. May be spherical in shape e. May be helical in shape f. Protect the viral nucleic acid g. Composed of subunits called capsomers h. May bind to the surface of the host cell

a. Composed entirely of protein b. May be an icosahedral shape e. May be helical in shape f. Protect the viral nucleic acid g. Composed of subunits called capsomeres h. May bind to the surface of the host cell Viral capsids are composed entirely of protein subunits called capsomers and form a covering which protects the nucleic acid core. Two very common shapes are helical and icosahedral. In addition to protecting the nucleic acid core, the capsid of some viruses binds to the surface of a host cell in the initial stages of establishing an infection.

Select the terms that describe the possible configurations of viral nucleic acids. Check all that apply. a. Single-stranded DNA b. Double-stranded DNA, linear c. Double-stranded DNA-RNA hybrid d. Double-stranded DNA, circular e. Single-stranded RNA, positive-sense f. Single-stranded RNA, negative-sense g. Double-stranded RNA

a. Single-stranded DNA b. Double-stranded DNA, linear d. Double-stranded DNA, circular e. Single-stranded RNA, positive-sense f. Single-stranded RNA, negative-sense g. Double-stranded RNA Viral nucleic acids display a large variety of configurations. Among DNA viruses, the DNA may be typical double-stranded DNA, either linear or circular, or it may be single-stranded DNA. RNA viruses may have double-stranded RNA or single-stranded RNA genomes. Depending on whether the single RNA strand is immediately ready for translation or has to be converted into the proper form, it is referred to as positive-sense RNA or negative-sense RNA, respectively.

Select all of the statements which provide reasons why it is controversial and difficult to assign species names to viruses. a. Some scientists argue that viruses are non-organisms and therefore can't be given species names. b. Viral genetics are poorly understood. c. Viruses don't possess ribosomal RNA. d. Viruses are too changeable.

a. Some scientists argue that viruses are non-organisms and therefore can't be given species names. d. Viruses are too changeable. While most scientists agree on classifying viruses into orders, families, and genera, the concept of viral "species" has been controversial. Some scientists argue that viruses aren't truly living things, that they are "non-organisms" and therefore can't be speciated. Also, viruses change readily and characteristics that might be used for speciation might change over time.

Virus X can infect rodents and birds, whereas Virus Y infects humans. Which has a broader host range? a. Virus X b. Virus Y

a. Virus X Virus X has a broader host range because it can infect many types of animals rather than just a human host.

Analyze the statements below, and select those that correctly apply to the unique characteristics of viruses. a. Viruses are species-specific and infect cells from all five kingdoms. b. Viruses are considered living because they can direct their own multiplication as well as the behavior of living cells. c. Viruses have a nucleic acid genome; however, it may be either DNA or RNA and the nucleic acids may be single or double stranded. d. While viruses are not considered living because they cannot direct their own multiplication, they are more than simply an aggregate of macromolecules since they can direct the behavior of living cells. e. Some viruses are parasitic, but others carry ribosomes in their capsid allowing them to translate their own proteins.

a. Viruses are species-specific and infect cells from all five kingdoms. c. Viruses have a nucleic acid genome; however, it may be either DNA or RNA and the nucleic acids may be single or double stranded. d. While viruses are not considered living because they cannot direct their own multiplication, they are more than simply an aggregate of macromolecules since they can direct the behavior of living cells.

Select all of the facts that support the concept that viruses are living. a. Viruses can direct life processes within a cell. b. Viruses are not able to reproduce outside of a host cell. c. Viruses have DNA or RNA, but not both. d. Viruses are unable carry out metabolic processes to generate ATP. e. Viruses do not have a cellular structure. f. Viruses have genetic material that determines their traits. g. Viruses can reproduce provided they have a host cell. h. Viruses can evolve.

a. Viruses can direct life processes within a cell. f. Viruses have genetic material that determines their traits. g. Viruses can reproduce provided they have a host cell. h. Viruses can evolve. The ongoing debate regarding whether viruses are truly alive continues. Some of the evidence that supports the "viruses are alive" concept includes that fact that they can direct life processes within their host cell, they have genetic material that determines their traits, they can reproduce, albeit within a host cell, and they can evolve.

What percentage of human DNA is thought to consist of viral DNA sequences? a. 40-80 b. 10-20 c. 0 d. 100

b. 10-20

Why do antiviral medications often have side effects? a. Most antiviral target cell membranes, a structure found on both virus particles and human cells. b. Viruses are intracellular pathogens, and therefore, there is often host cell damage with antiviral treatments. c. When viral metabolism is restricted, the host cell will die.

b. Viruses are intracellular pathogens, and therefore, there is often host cell damage with antiviral treatments. Because viruses are intracellular agents that take over host cells and their functions, the host cells themselves usually suffer damage with the use of treatments designed to target the virus.

Select the statement that accurately reflects the characteristics of viral capsids. a. Together with the viral envelope, it forms the nucleocapsid. b. They are made of lipids. c. Animal viruses exhibit helical or icosahedral capsids. d. They are constructed of identical centromeres.

c. Animal viruses exhibit helical or icosahedral capsids. Viral capsids are made up of proteins and are constructed of repeating units called capsomers. Together with the nucleic acid in the virus, it forms the nucleocapsid.

Choose the primary reason why it is more difficult to design antiviral drugs than antibacterial drugs. a. Antiviral drugs can't readily penetrate host cells. b. Antiviral drugs must target viral envelopes and capsids. c. Antiviral drugs often must target host cell functions, which results in side effects in the host. d. Viral cell structure is different than bacterial cell structure.

c. Antiviral drugs often must target host cell functions, which results in side effects in the host. Since viruses rely on host cell functions to reproduce, it is often these host cell functions that are targeted by antiviral drugs, and this can cause side effects. This is not the case with antibacterial drugs, which target bacterial cell structures or functions that are not present in eukaryotic host cells.

Why are CD4 counts related to HIV infection? a. HIV needs CD4 molecules for replication. b. HIV destroys CD4 molecules found on T cells. c. HIV can only bind to cells with CD4 receptors.

c. HIV can only bind to cells with CD4 receptors. HIV glycoproteins bind to CD4 receptors on certain white blood cells to cause infection and eventual destruction of those cells.

Enveloped viruses use glycoproteins called _______ to specifically bind with their host cells. a. capsomers b. capsids c. spikes d. tail fibers

c. spikes Glycoprotein spikes are used by enveloped viruses for attachment to host cell receptors. This is a specific interaction, limiting the host range of the virus.

If you could design a drug to "hide" or block sialic acid on respiratory cells, what stage of the life cycle of influenza would be directly impacted? a. Release b. Assembly c. Synthesis d. Adsorption

d. Adsorption Sialic acid is the cell receptor used by influenza for attachment to host cells. Blocking this would block adsorption of the virus to host cells.

Rather than developing more antiviral medications, what is a more common focus for researchers when it comes to viral disease? a. Designing bacteriophages b. Reducing induction triggers for persistent infections c. Designing drugs to minimize CPEs d. Vaccine development

d. Vaccine development Vaccine development for the prevention of viral disease has historically been the focus for scientists.

Rabies virus has a _______ host range as compared to hepatitis B virus. a. narrow b. restricted c. medium d. broad

d. broad Rabies can infect all mammals whereas hepatitis B is restricted to human hosts.

Which drug targets can be found on both bacterial cells and viral particles? a. Cell wall b. Protein synthesis machinery c. Metabolic pathways d. None of these are possessed by bacteria. e. None of these are possessed by viruses

e. None of these are possessed by viruses Viral particles have none of these cellular targets. Therefore, antibiotics do not work against viral infections.

Antiviral drugs available today include those designed to block _________________ and processing, _________ packaging and, in the case of HIV, block the action of the enzyme ___________________________.

protein synthesis genome reverse transcriptase

Antibiotics that destroy bacterial cells ideally exhibit _____________, that is, they target cellular components that the infected human cells lack, such as ______________ and 70s ribosomes. It is more difficult to design _____________ since viruses cannot replicate without a host; therefore, by necessity the drug must penetrate the host cell, often causing severe ___________ in the process.

selective toxicity cell walls antiviral drugs side effects

Since it is easier for scientists to orchestrate viral disease prevention rather than cure, generally more effort is directed towards ________________ production than antiviral drug development.

vaccine