AP Biology : Understanding Viruses and Prions

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #65 : Microorganisms And Viruses

Which of the following nucleic acids codes for viral genomes?

Possible Answers:

Single-stranded DNA

Any of the other answer choices

Double-stranded RNA

Double-stranded DNA

Single-stranded RNA

Correct answer:

Any of the other answer choices

Explanation:

A virus may contain any of these four types of genetic material. The type of nucleic acid, and whether it is single- or double-stranded, determines how the virus integrates with the host organism. Different classes of viruses have different mechanisms for infection.

Note that retroviruses, which contain single-stranded RNA that is later converted to DNA, are often classified as a fifth type of virus.

Example Question #66 : Microorganisms And Viruses

Which of the following explains why viruses are not considered alive?

Possible Answers:

Viruses do not metabolize ATP

They take advantage of host ribosomes for protein synthesis

Viruses possess either RNA or DNA; never both

All of the choices are correct

Correct answer:

All of the choices are correct

Explanation:

There are a multitude of reasons as to why viruses are not classified as living organisms. In addition to the reasons given, viruses require host reproductive organelles and proteins in order to multiply. They also are not separated from the external world by a membrane or cell wall.

Example Question #71 : Microorganisms And Viruses

Human immunodeficiency virus (HIV) principally attacks which type of cell?

Possible Answers:

White blood cells

Red blood cells

Microglial cells

Beta cells

Pancreatic acinar cells

Correct answer:

White blood cells

Explanation:

Human immunodeficiency virus (HIV), which is the causative agent of AIDS, primarily attacks the white blood cells. More specifically, it infects helper T-cells, macrophages, and dendritic cells. By damaging the cells of the immune system the virus creates an "immunodeficiency," weakening the body's ability to fight infection.

Example Question #11 : Understanding Viruses And Prions

Of the following types of molecules, which is always found in virions?

Possible Answers:

Carbohydrate

Protein

Lipid

DNA

RNA

Correct answer:

Protein

Explanation:

Virus particles, otherwise known as virions, always contain proteins. Whether they contain DNA or RNA depends solely upon the type of virion; different types of viruses will carry different types of nucleic acids. The capsids of virions contain proteins that surround the nucleic acids, whether it be DNA or RNA.

Example Question #12 : Understanding Viruses And Prions

HIV is a RNA virus that affects millions of humans worldwide. Which of the following will an HIV virus contain?

I. DNA-dependent RNA polymerase

II. RNA-dependent DNA polymerase

III. DNA-dependent DNA polymerase

Possible Answers:

II only

II and III

I only

I and II

Correct answer:

II and III

Explanation:

The question states that HIV is a RNA virus; therefore, the virus must possess an enzyme that transforms the RNA genome into DNA. This enzyme is called reverse transcriptase. Since it transforms RNA to DNA it is also called an RNA-dependent DNA polymerase.

DNA-dependent RNA polymerase (required for transcription) is not present in HIV because it is not a DNA virus.

Finally, HIV does contain DNA-dependent DNA polymerase. This enzyme is required for DNA replication, which is an important process in HIV replication.

Example Question #13 : Understanding Viruses And Prions

RNA viruses are classified as either plus-strand RNA or minus-strand RNA viruses. Which of the following describes the main difference between these two types of viruses?

Possible Answers:

Minus-strand RNA can be translated directly into proteins, but plus-strand RNA can’t

Minus-strand RNA has introns, but plus-strand RNA doesn’t

Plus-strand RNA has introns, but minus-strand RNA doesn’t

Plus-strand RNA can be translated directly into proteins, but minus-strand RNA can’t

Correct answer:

Plus-strand RNA can be translated directly into proteins, but minus-strand RNA can’t

Explanation:

Plus-strand RNA viruses can directly translate their RNA into proteins, however minus-strand RNA viruses require an additional step before translation. The minus-strand RNA is a complement to mRNA; therefore, minus-strand RNA must be transcribed into plus-strand RNA before translation. This step is the key difference between plus-strand and minus-strand RNA viruses.

You can eliminate the answer choices involving introns because most viruses do not contain introns. The viruses that contain introns could be either plus-strand or minus-strand RNA viruses (or DNA viruses).

Example Question #11 : Understanding Viruses And Prions

Which of the following will you not find inside the capsid of a virion?

I. Nucleic acids

II. Amino acids

III. Ribosomes

Possible Answers:

I and II

III only

II and III

II only

Correct answer:

III only

Explanation:

The capsid of a virion is the region that contains the viral DNA or RNA and the necessary enzymes that facilitate infection of a host cell. When a virion infects a cell, the contents of the capsid are injected into the host cell. This marks the onset of infection. A capsid contains nucleic acids (DNA or RNA) and amino acids (enzymes).

A virion does not contain ribosomes or any other organelles. Instead, the virus must use host cell machinery to translate the proteins required for replication.

Example Question #14 : Understanding Viruses And Prions

Which nucleic acid can be found in a virus?

Possible Answers:

Double-stranded DNA

Single-stranded RNA or DNA

Double-stranded RNA or DNA

Single-stranded RNA

Any of these could be found in a virus

Correct answer:

Any of these could be found in a virus

Explanation:

Viral genomes are incredibly diverse. Different types of viruses use different genetic materials. Viruses are capable of using double-stranded DNA, double-stranded RNA, single-stranded DNA, or single-stranded RNA.

Example Question #15 : Understanding Viruses And Prions

Researchers analyze a rare virus. They find that the virus contains reverse transcriptase and has a latent period of three years. Based on this information what can you conclude?

Possible Answers:

Upon infection, the virus injects RNA into the cell and goes into the lytic cycle

Upon infection, the virus injects DNA into the cell and goes into the lysogenic cycle

Upon infection, the virus goes into the lysogenic cycle, but the type of genetic material cannot be determined

Upon infection, the virus injects DNA into the cell and goes into the lytic cycle

Upon infection, the virus injects RNA into the cell and goes into the lysogenic cycle

Correct answer:

Upon infection, the virus injects RNA into the cell and goes into the lysogenic cycle

Explanation:

Remember that reverse transcriptase is an enzyme that facilitates the generation of DNA from RNA. A virus containing reverse transcriptase must initially possess an RNA genome. Once inside the host cell the virus generates complementary DNA from the RNA template. You can eliminate the choices involving DNA.

A very long latent period of three years suggests that the virus undergoes the lysogenic cycle. The lytic cycle involves immediate lysis of the host cell and spread of infection after viral replication. In contrast, the lysogenic cycle causes the virus to become dormant. One of the main characteristics of a virus in the lysogenic cycle is that it has a long latent period.

Example Question #16 : Understanding Viruses And Prions

Daniel’s dog has always been healthy and maintained an average weight. Suddenly, the dog begins losing weight even though he is eating and exercising the usual amount. A tapeworm is found within the intestines of a dog. This tapeworm is an example of which of the following?

Possible Answers:

Endoparasite

Parasitism

Commensalism 

Mutualism

Ectoparasite

Correct answer:

Endoparasite

Explanation:

Endoparasites, like the tapeworm, live in the body of their host and deprive the host of nutrients, often leading to sickness as seen in Daniel’s dog. Ectoparasites live and feed on the external surface of their host. Symbiotic relationships are those where two individuals are living in direct and intimate contact with one another, such as a parasite and its host. Mutualism and commensalism are a type of symbiotic relationship in which one or both species in the symbiotic relationship benefit and no one is harmed. 

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