AP Biology : Understanding Viruses and Prions

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #21 : Understanding Viruses And Prions

Which of the following is true of a bacteriophage?

Possible Answers:

It always contain a circular DNA plasmid

It can infect only plants or fungi

It contains its own ribosomes

It is engulfed entirely by the host cell

Only its DNA enters the host cell

Correct answer:

Only its DNA enters the host cell

Explanation:

A bacteriophage is a virus which attacks bacteria and consists of a head, tail, and tail fibers all made of protein. The head contains genetic material (usually linear DNA) which is injected into the host bacterium upon infection. The protein parts do not enter the bacterium, and it does not have any ribosomes or organelles of its own.

Example Question #959 : Ap Biology

Some vaccines are developed through attenuation of the actual viral organism. Attenuation occurs through giving the pathogen a nutrient rich environment to replicate in thus mutation occurs in virulence factors normally adapted by the virus for survival.

Which of these is a reason attenuation of the West Nile Virus for a suitable human vaccine has not occurred as yet?

Possible Answers:

A chicken can develop the symptoms and an immune response to the West Nile Virus thus putting the virus back into competition to remain virulent

A horse can develop the symptoms and an immune response to the West Nile Virus thus putting the virus back into competition to remain virulent

Neuronal cell culture techniques have been unsuccessful in surviving replication of the virus

All of these

Human blood cell lines can are a target of the West Nile Virus thus putting the virus back into competition to remain virulent

Correct answer:

All of these

Explanation:

The three main media of attenuating a virus are infecting birds, horses, or cultured cell lines. West Nile Virus is an interesting virus in that host and susceptible organisms happen to be birds, horses, and humans. This virus also does not seem to replicate in other animal reservoirs such as lizards. It does not replicate in mosquitos. Moreover, recent attempts to culture a neuronal cell line to replicate the virus have been unsuccessful due to the extended length of life cycle of neuronal cells.

Example Question #22 : Understanding Viruses And Prions

What novel enzyme to retroviruses employ to convert their RNA genomes into DNA?

Possible Answers:

Reverse translatase

DNA synthase

DNA polymerase

Reverse transcriptase

RNA replicase

Correct answer:

Reverse transcriptase

Explanation:

Retroviruses employ the enzyme reverse transcriptase to convert their RAN genomes into DNA.

Example Question #22 : Understanding Viruses And Prions

Which of the following describes the enzyme reverse transcriptase?

Possible Answers:

An RNA dependent DNA polymerase

A DNA dependent RNA polymerase

An RNA dependent RNA polymerase

A DNA dependent DNA polymerase

An RNA dependent protein polymerase

Correct answer:

An RNA dependent DNA polymerase

Explanation:

Reverse transcriptase binds RNA and catalyzes the formation of a complementary DNA molecule. Since it needs an RNA template to work, this enzyme is RNA dependent. Since it forms a DNA molecule, this enzyme is a DNA polymerase. Recall the chemical difference between DNA and RNA - DNA lacks a hydroxide group at the 3' position of the ribose sugar, which makes it deoxyribose.

Example Question #23 : Understanding Viruses And Prions

Which of the following do retroviruses and bacteriophages have in common?

Possible Answers:

They can both enter the lysogenic cycle

The both have only RNA genomes

They both only infect prokaryotes

The both use reverse transcriptase

They can both enter the lytic cycle

Correct answer:

They can both enter the lysogenic cycle

Explanation:

The lysogenic cycle occurs when a virus incorporates its DNA into the host genome. It stays inside the host genome, getting replicated along with the host until conditions are right when it excises itself and beings the process of hijacking the cell to make more virus. Both retroviruses and bacteriophages can undergo this process.

Example Question #24 : Understanding Viruses And Prions

Prions represent misfolded versions of what biological macromolecule?

Possible Answers:

Carbohydrates

Nucleic acids

Proteins

Vitamins

Lipids

Correct answer:

Proteins

Explanation:

Prions are proteins that are folded in alternate conformations. The molecules can then produce a disease state by catalyzing the misfolding of additional proteins in the cell. Note that vitamins are not one of the four classical biological macromolecules.

Example Question #25 : Understanding Viruses And Prions

Viral genomes may consists of which of the following nucleic acids?

I. Double-stranded DNA

II. Single-stranded DNA

III. Double-stranded RNA

IV. Single-stranded RNA

Possible Answers:

I, II, and III

II, III, and IV

I and II

I, II, III, and IV

I and IV

Correct answer:

I, II, III, and IV

Explanation:

The nucleic acids that make up viral genomes are very diverse. Viral genome can consist of both double and single stranded DNA as well as double and single stranded RNA.

Example Question #26 : Understanding Viruses And Prions

Reverse transcriptase is __________.

Possible Answers:

produced by viruses and is used to inhibit normal DNA transcription

produced by the infected cell and used to inhibit viral transcription

produced by viruses and used by the infected cell to transcribe viral RNAs that will be translated by the cell into viral proteins

produced by viruses and used by the cell to transcribe viral DNA that will be inserted into the genome of the infected cell

produced by the infected cell and used to transcribe RNAs that will be translated by the cell into antibodies against viruses

Correct answer:

produced by viruses and used by the cell to transcribe viral DNA that will be inserted into the genome of the infected cell

Explanation:

Reverse transcriptase is a viral enzyme used by some viruses to transcribe double-stranded DNA from their single-stranded RNA, which is the exact opposite of the normal transcription process of the cell. The double-stranded viral DNA is then able to integrate into the double-stranded DNA of the infected cell’s genome so that whenever the cell divides, all of its daughter cells will carry the viral DNA. This viral DNA can eventually be transcribed by the cell’s own enzymes to produce viral RNA. Some of the viral RNA will be translated into viral proteins, and new viruses will be assembled from these products.

Example Question #27 : Understanding Viruses And Prions

Which of the following is not true about viruses?

Possible Answers:

In the lytic cycle, the new viruses break out from the cell, killing its host. 

In the lysogenic cycle, the virus replicates its genome and kills its host. 

In the lysogenic cycle, the viral genome is embodied into the bacterial chromosome through genetic recombination.

Some viruses only use the lytic cycle.

In the lysogenic cycle, the virus replicates its genome without killing its host. 

Correct answer:

In the lysogenic cycle, the virus replicates its genome and kills its host. 

Explanation:

In the lysogenic cycle, a virus replicates its genome but does not kill the host. The host lives and reproduces normally, and the daughter cells can inherit the prophage (the bacterial circular chromosome and the bacteriophage genome)

Example Question #28 : Understanding Viruses And Prions

Which of the following is characteristic of viruses?

Possible Answers:

Cell wall made of chitin

Membrane bound organelles (e.g., Golgi apparatus)

Thick peptidoglycan cell wall

Lipid bilayer outer membrane

A protein coat

Correct answer:

A protein coat

Explanation:

Viruses are unique organisms in that they have a relatively simple cell structure. They have an outer protein coat, which sets them apart from other organisms. Peptidoglycan is found in bacteria, lipid bilayer is found in eukaryotic cells, and chitin is found in fungi. Membrane-bound orangelles are found in more complex cells, such as eukaryotic cells, and are not unique to viruses.

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