Enlighten Knowledge Exam, Sample subjective questions on Viruses, Bacteria, and Archaea


What are the two components shared by all viruses?

All viruses have;

  • a nucleic acid
  • and a capsid.

Viruses are generally considered to be non-living. Should Viroids and prions also be viewed as non-living? Why or why not?

Viroids and prions are non-living because, like viruses, they are noncellular and unable to reproduce without a host

From an evolutionary standpoint, why is it beneficial to a virus if its host lives and does not die?

If a virus’ host survives, many more copies of the virus will be produced and spread to other hosts than if the host dies.

How is a prokaryotic cell structurally different from a eukaryotic cell?

Prokaryotic cells lack a nucleus and membranous organelles.

Where is the cell wall located relative to the plasma membrane in a typical prokaryotic cell?

The cell wall lies outside the plasma membrane.

How is conjugation different from sexual reproduction?

In conjugation, the recipient prokaryotic cell acquires new DNA from the donor cell. Sexual reproduction occurs in eukaryotes and results in a new individual with a haploid set of chromosomes from each parent.

How is the peptidoglycan layer different in Gram-positive and Gram-negative cells?

The peptidoglycan layer is much thicker in Gram-positive cells than in Gram-negative cells.

What is the function of bacterial endospores?

Endospores permit survival when environmental conditions are harsh.

Which bacteria produce much of the oxygen we breathe, and what metabolic process gives off this oxygen?

Cyanobacteria produce by photosynthesis much of the oxygen we breathe.

How are archaea different from bacteria?

Archaea and bacteria differ in rRNA base sequences, and their plasma membranes and cell walls are biochemically distinct.

List the three types of archaea distinguished by their unique habitats.

  • Methogens,
  • halophiles,
  • thermoacidophiles

 Archaea are thought to be closely related to eukaryotes. What evidence supports this possibility?

Archaea and eukaryotes share some of the same ribosomal proteins, initiate transcription in the same way, and have similar tRNA.

In a recent United Nations report, the practice of maintaining large herds of livestock was blamed for contributing to greenhouse gases. What is the basis for this claim?

Archaea that inhabit livestock intestines generate methane, a greenhouse gas.

What is the difference between a virulent phage and a temperate phage?

A virulent phage always enters the lytic cycle when it infects a bacterial cell.

The end result is the assembly of many progeny phages and their release into the surroundings when the cell breaks open.

A temperate phage enters either the lytic cycle or the lysogenic cycle when it infects a cell.

The lytic cycle is the same as that for a virulent phage.

The lysogenic cycle involves the integration of the phage’s chromosome into the bacterial chromosome.

In the integrated state, the phage now called the prophage is inactive and replicates only when the bacterial chromosome replicates.

In response to an adverse environmental signal to the cell, the phage chromosome can excise itself from the bacterial chromosome and enter the lytic cycle.

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How does viral infection of an animal cell and a plant cell differ?

Animal cells:

  • Viruses without an envelope bind by their recognition proteins to receptor proteins in the host cell’s plasma membrane and are then taken into the cell by receptor-mediated endocytosis.
  • For some enveloped viruses, the genome-containing capsid enters the cell when the envelope fuses with the host cell’s plasma membrane.
  • For other enveloped viruses, the complete virus, with the envelope, enters the cell by endocytosis.

Plant cells:

  • All plant viruses lack envelopes.
  • They enter cells either through mechanical injuries to leaves and stems or by the action of biting and feeding insects.

How are retroviruses distinctive among RNA viruses with respect to replication of their genome?

Non-retroviral RNA viruses have RNA genomes that are replicated in an RNA-to-RNA manner.

Retroviruses have RNA genomes that are replicated via a DNA inter- mediate; that is, the RNA genome is copied to double-stranded DNA by reverse transcriptase and the DNA molecule integrates into the host cell’s nuclear chromosomes, from which location new RNA viral genomes are transcribed.

While a few drugs are effective against some viruses, they often impair the function of body cells and thereby have a number of side effects. Most antibiotics (antibacterial drugs) do not cause side effects. Why would antiviral medications be more likely to produce side effects?

For the most part, viruses use host enzymes, which can cause side effects.

Model organisms are those widely used by researchers who wish to understand basic processes that are common to many species. Bacteria such as Escherichia coli are model organisms for modern geneticists. Compare the characteristics of bacteria to those of peas and give three reasons why bacteria would be useful in genetic experiments.

  • Bacteria are very small and reproduce very rapidly, so it is possible to produce and keep many generations in a small test tube or petri dish.
  • Having only one set of genes means that any new mutations show immediately and can be more easily analyzed.
  • Lastly, plasmids can be used as a highly effective vector in genetic engineering experiments.

Why can’t dogs catch the measles?

The virus can’t attach to dog cells, because dog cells do not express the receptors for the virus, and/ or there is no cell within the dog that is permissive for viral replication.

One of the first and most important targets for drugs to fight infection with HIV (a retrovirus) is the reverse transcriptase enzyme. Why?

  • Reverse transcriptase is needed to make more HIV-1 viruses, so targeting the reverse transcriptase enzyme may be a way to inhibit the replication of the virus.
  • Importantly, by targeting reverse transcriptase, we do little harm to the host cell, since host cells do not make reverse transcriptase.
  • Thus, we can specifically attack the virus and not the host cell when we use reverse transcriptase inhibitors.

Although plant viruses cannot infect humans, what are some of the ways in which they affect humans?

Plant viruses infect crops, causing crop damage and failure, and considerable economic losses.

Why is immunization after being bitten by a rabid animal so effective and why aren’t people vaccinated for rabies like dogs and cats are?

Rabies vaccine works after a bite because it takes a week for the virus to travel from the site of the bite to the central nervous system, where the most severe symptoms of the disease occur.

Adults are not routinely vaccinated for rabies for two reasons:

  • first, because the routine vaccination of domestic animals makes it unlikely that humans will contract rabies from an animal bite;
  • second, if one is bitten by a wild animal or a domestic animal that one cannot confirm has been immunized, there is still time to give the vaccine and avoid the often fatal consequences of the disease.

How are Viroids like viruses?

They both replicate in a cell, and they both contain nucleic acid.

Why do scientists believe that the first organisms on Earth were extremophiles?

Because the environmental conditions on Earth were extreme:

  • high temperatures,
  • lack of oxygen,
  • high radiation, and the like.

Mention three differences between bacteria and archaea.

  • Bacteria contain peptidoglycan in the cell wall; archaea do not.
  • The cell membrane in bacteria is a lipid bilayer; in archaea, it can be a lipid bilayer or a monolayer.
  • Bacteria contain fatty acids on the cell membrane, whereas archaea contain phytanyl.

Explain the statement that both types, bacteria and archaea, have the same basic structures, but are built from different chemical components.

  • Both bacteria and archaea have cell membranes and they both contain a hydrophobic portion.
  • In the case of bacteria, it is a fatty acid; in the case of archaea, it is a hydrocarbon (phytanyl).
  • Both bacteria and archaea have a cell wall that protects them.
  • In the case of bacteria, it is composed of peptidoglycan, whereas in the case of archaea, it is pseudo peptidoglycan, polysaccharides, glycoproteins, or pure protein.
  • Bacterial and archaeal flagella also differ in their chemical structure.

Think about the conditions (temperature, light, pressure, and organic and inorganic materials) that you may find in a deep-sea hydrothermal vent. What type of prokaryotes, in terms of their metabolic needs (autotrophs, phototrophs, chemotrophs, etc.), would you expect to find there?

  • In a deep-sea hydrothermal vent, there is no light, so prokaryotes would be chemotrophs instead of phototrophs.
  • The source of carbon would be carbon dioxide dissolved in the ocean, so they would be autotrophs.
  • There is not a lot of organic material in the ocean, so prokaryotes would probably use inorganic sources, thus they would be chemoautotrophs.
  • The temperatures are very high in the hydrothermal vent, so the prokaryotes would be thermophilic.

Explain the reason why the imprudent and excessive use of antibiotics has resulted in a major global problem.

  • Antibiotics kill bacteria that are sensitive to them; thus, only the resistant ones will survive.
  • These resistant bacteria will reproduce, and therefore, after a while, there will be only resistant bacteria.

Researchers have discovered that washing spinach with water several times does not prevent foodborne diseases due to E. coli. How can you explain this fact?

  • coli colonizes the surface of the leaf, forming a biofilm that is more difficult to remove than free (planktonic) cells.
  • Additionally, bacteria can be taken up in the water that plants are grown in, thereby entering the plant tissues rather than simply residing on the leaf surface.

Your friend believes that prokaryotes are always detrimental and pathogenic. How would you explain to them that they are wrong?

  • Remind them of the important roles’ prokaryotes play in decomposition and freeing up nutrients in biogeochemical cycles;
  • Remind them of the many prokaryotes that are not human pathogens and that fill very specialized niches.
  • Furthermore, our normal bacterial symbionts are crucial for our digestion and in protecting us from pathogens.

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