Which of the following does not initiate DNA synthesis?
a. a double-stranded DNA virus (Poxviridae)
b. a DNA virus with reverse transcriptase (Hepadnaviridae)
c. an RNA virus with reverse transcriptase (Retroviridae)
d. a single-stranded RNA virus (Togaviridae)
e. none of the above

Verified step by step guidance

1. Identify the key requirement for DNA synthesis initiation, which is the presence of a DNA template.
2. Analyze each option to determine if it involves a DNA template or a mechanism to synthesize DNA.
3. Option a: Double-stranded DNA virus (Poxviridae) - This virus has a DNA template, so it can initiate DNA synthesis.
4. Option b: DNA virus with reverse transcriptase (Hepadnaviridae) - This virus uses reverse transcriptase to convert its DNA into a form that can be replicated, thus initiating DNA synthesis.
5. Option c: RNA virus with reverse transcriptase (Retroviridae) - This virus uses reverse transcriptase to convert its RNA into DNA, which can then be used as a template for DNA synthesis.

Key Concepts

DNA Synthesis Initiation

DNA synthesis initiation refers to the process by which DNA replication begins. This process typically requires specific enzymes, such as DNA polymerases, and is often initiated at origins of replication. Certain viruses can hijack host cellular machinery to initiate their own DNA synthesis, but not all viruses possess this capability.

Types of Viruses

Viruses can be classified based on their genetic material and replication mechanisms. DNA viruses, like those in the Poxviridae and Hepadnaviridae families, directly use DNA for replication. In contrast, RNA viruses, such as those in the Retroviridae and Togaviridae families, may require reverse transcription to convert their RNA into DNA before replication can occur.

Reverse Transcriptase

Reverse transcriptase is an enzyme that synthesizes DNA from an RNA template, a process crucial for certain viruses, particularly retroviruses. This enzyme allows RNA viruses to integrate their genetic material into the host's DNA, facilitating replication. Understanding the role of reverse transcriptase is essential for distinguishing which viruses can initiate DNA synthesis.