Question

Which of the following types of nucleic acid will never be found in a virus? A. Single-stranded DNA B. Double-stranded DNA C. Single- and double-stranded RNA D. All of these can be found in a virus.

Short answer

D: All of these can be found in a virus.

Step-by-step solution

Understand the question

Determine which types of nucleic acids are being considered: Single-stranded DNA, Double-stranded DNA, Single-stranded RNA, and Double-stranded RNA. The task is to identify which nucleic acid type will never be found in a virus.

Evaluate Single-stranded DNA

Single-stranded DNA (ssDNA) can be found in certain viruses. For instance, the Parvoviridae family of viruses contains single-stranded DNA.

Evaluate Double-stranded DNA

Double-stranded DNA (dsDNA) is also found in viruses. Examples include the Herpesviridae family, which has a double-stranded DNA genome.

Evaluate RNA Forms

Both Single-stranded RNA (ssRNA) and Double-stranded RNA (dsRNA) are present in viruses. For example, the Retroviridae family has single-stranded RNA, while the Reoviridae family has double-stranded RNA.

Conclusion

Since all the listed forms of nucleic acids (ssDNA, dsDNA, ssRNA, dsRNA) can be found in various viruses, none of them can be excluded as a possibility.

Choose the correct answer

Based on the evaluation, the correct answer is D: All of these can be found in a virus.

Key concepts

single-stranded DNA in viruses

Certain viruses have single-stranded DNA (ssDNA) as their genetic material. This is less common than double-stranded DNA, but it does occur. A prominent example is the Parvoviridae family.

These viruses are small and simple, often infecting animals, including humans and pets. Parvoviruses are known to cause various diseases such as fifth disease in humans and canine parvovirus in dogs.

Viruses with ssDNA must convert their genome into a double-stranded form before replication can occur in the host cell. This conversion is crucial since the host's replication machinery usually recognizes double-stranded DNA.

• Parvoviridae: The main family with ssDNA.
  
• Must convert to dsDNA: Essential for replication.
  

double-stranded DNA in viruses

Double-stranded DNA (dsDNA) is more common in viruses and can be found in several virus families. These viruses have a more complex structure and often cause more severe diseases. A well-known example is the Herpesviridae family.

Herpesviruses can remain dormant in the host cells and reactivate later. This ability results in chronic and recurrent infections. Other examples include the Poxviridae family, which includes the variola virus responsible for smallpox.

DS DNA viruses use the host's cellular mechanisms to replicate their genome. They often integrate their DNA into the host's genome, making them harder to eliminate.

• Herpesviridae: Known for causing herpes simplex and varicella-zoster (chickenpox and shingles).
  
• Poxviridae: Includes the smallpox-causing variola virus.
  
• Larger genomes: Often lead to more complex interactions with the host.
  

RNA in viruses

RNA viruses have RNA as their genetic material, which can be either single-stranded (ssRNA) or double-stranded (dsRNA). Each type has different ways of infecting host cells and replicating.

Single-stranded RNA (ssRNA) viruses include retroviruses like HIV, which use reverse transcription to convert their RNA into DNA inside the host cell. This DNA can integrate into the host genome, becoming a part of the host's genetic material. Double-stranded RNA (dsRNA) viruses, like those in the Reoviridae family, include rotaviruses, which cause severe diarrheal diseases.

The RNA structure allows for rapid mutations, which can make these viruses particularly challenging to combat due to their adaptability.

• Retroviridae (ssRNA): Includes HIV.
  
• Reoviridae (dsRNA): Includes rotaviruses.
  
• High mutation rates: Lead to quick adaptability and often resistance to treatments.
  

viral genome composition

Viruses can have diverse genome compositions, including DNA or RNA, and single-stranded or double-stranded forms. This diversity allows viruses to infect a wide variety of hosts and adapt to different environmental conditions.

The type of nucleic acid in a virus determines its replication strategy and the complexity of its lifecycle. For example, ssDNA viruses must convert their genome into dsDNA to replicate, while ssRNA viruses may use reverse transcription.

Understanding the viral genome composition is crucial for developing treatments and vaccines. Many antiviral drugs target specific steps in the viral replication process, which vary depending on the genome type.

• Diverse genome types: Include ssDNA, dsDNA, ssRNA, and dsRNA.
  
• Influences replication strategy: Different mechanisms based on genome type.
  
• Key for treatment development: Helps target specific viral replication steps.