Question

The early genes of DNA viruses code primarily for proteins whose functions are required for: A. transcription of viral mRNA. B. translation of the capsid proteins. C. replication of the viral DNA. D. final uncoating of the infecting virions. E. processing of the mRNA precursors

Short answer

The early genes of DNA viruses code primarily for proteins whose functions are required for the transcription of viral mRNA (Option A) and replication of the viral DNA (Option C).

Step-by-step solution

Understanding viral life cycle

The life cycle of viruses involves several steps: adsorption, penetration, uncoating, replication, assembly, and release. These steps involve both early and late genes of the virus, coding for different proteins with distinct functions.

Early genes function

In the early phase of the viral life cycle, early genes of the virus are transcribed and translated. These proteins are usually non-structural and are involved in preparing the cell for viral DNA replication and regulation of the host cellular environment. This means they are crucial for processes such as the transcription of viral mRNA and replication of the viral DNA.

Evaluate the options

Option A relates to the transcription of viral mRNA which can be performed by proteins coded by early genes. Option B, C, D, and E are generally associated with later stages in the viral life cycle, pertaining to processes like the translation of capsid proteins, final uncoating of the infecting virions, and processing of the mRNA precursors. Among these, the replication of viral DNA (Option C) can also be an activity of proteins produced by early genes.

Select correct options

Based on the functions of early genes, it can be concluded that the proteins coded by the early genes of DNA viruses are primarily required for the transcription of viral mRNA (Option A) and replication of the viral DNA (Option C).

Key concepts

Viral Life Cycle

The viral life cycle is a series of steps that viruses go through to multiply and infect host cells. This cycle generally consists of six primary stages:

• Adsorption: The virus attaches to the host cell's surface through specific interactions between viral proteins and cell receptors.
• Penetration: The virus or its genetic material enters the host cell, often via endocytosis or membrane fusion.
• Uncoating: This step involves the disassembly of the viral capsid, releasing the viral genome into the host cell.
• Replication: The viral genome is replicated, producing new copies of the virus's genetic material.
• Assembly: New viral particles are assembled from the newly synthesized proteins and replicated genomes.
• Release: The newly formed viruses are released from the host cell, either by cell lysis or budding, to infect new cells.

In these stages, the roles of early and late viral genes differ. Early genes are critical in the initial stages, especially during replication, where they set the stage for successful multiplication and infection.

Early Genes Function

Early genes play a pivotal role at the start of the viral life cycle. These genes are expressed soon after the virus enters a host cell and are essential for initiating the processes necessary for viral replication.
Typically, early genes encode for non-structural proteins. Their functions include:

• Transcription Regulation: Early gene products can modify the host's transcription machinery to support viral mRNA synthesis.
• DNA Replication Support: They help prepare the host cell for viral DNA replication by modifying host cell conditions or directly participating in the replication process.
• Cellular Environment Modification: These proteins may alter the host cell's metabolic processes to favor the viral life cycle over normal cell functions.

By fulfilling these roles, early genes ensure the virus can successfully take over and utilize the host's cellular machinery for its own replication and assembly.

Transcription and Replication in Viruses

Transcription and replication are core processes during a viral infection, particularly for DNA viruses. These processes are crucial for generating the viral components needed to produce new viruses.
Transcription of Viral mRNA:

• For DNA viruses, transcription entails the synthesis of viral mRNA from the viral DNA template.
• This mRNA is then translated into viral proteins by the host cell's ribosomes.
• Early genes are primarily responsible for ensuring that transcription mechanisms are in place to generate necessary viral proteins early in the infection.

Replication of Viral DNA:

• Viral DNA replication involves copying the viral genome to produce multiple copies for packaging into new virus particles.
• Early gene products often play a role in facilitating conditions within the host cell that favor viral DNA replication.
• By ensuring successful replication, viruses prepare for the assembly and release of numerous progeny viruses.

Together, these phases ensure the production of all necessary components for the virus to express its full life cycle and propagate the infection.