Question

Some viral genomes, composed of single-stranded RNA, act as mRNA. What advantage might these viruses have over other kinds of viruses?

Short answer

Viruses with single-stranded RNA genomes that act as mRNA have a speed advantage. They can directly produce proteins once they enter a host cell, bypassing the need for transcription from DNA to RNA. This could potentially allow them to multiply and spread more quickly than viruses that need to undergo this additional process.

Step-by-step solution

Understand the role of mRNA

Firstly, mRNA, or messenger RNA, carries genetic information from the DNA in the cell nucleus to the cytoplasm, where it can be used to produce proteins. This is a crucial part of gene expression.

How mRNA benefits the virus

In the case of viruses, if their genome acts as mRNA, it means they can directly produce proteins once they enter a host cell. It gives these types of viruses a speed advantage because they bypass the need for transcription from DNA to RNA.

Advantage over other types of viruses

Other types of viruses, such as those with DNA genomes or double-stranded RNA, first need to be transcribed into mRNA before they can produce proteins. This additional step not only takes more time but also requires more energy and resources from the host cell. Therefore, viruses with single-stranded RNA genomes acting as mRNA would have a speed advantage, which could enable them to multiply and spread more quickly.

Key concepts

Messenger RNA Function

The function of messenger RNA (mRNA) is central to the process of gene expression, the pathway by which genetic information is converted into functional products like proteins. mRNA is like a recipe or blueprint–it takes instructions from DNA, which contains the comprehensive genetic code, and conveys this information to the ribosomes in the cytoplasm. In the ribosomes, the sequence of nucleotides in mRNA is translated into the sequence of amino acids that make up proteins.

This process starts with transcription in the cell's nucleus where a DNA strand is used as a template to create a complementary RNA strand. The RNA strand then undergoes several modifications to become mRNA. Once complete, mRNA exits the nucleus and participates in protein synthesis. It's this function that is hijacked by certain RNA viruses to initiate the production of viral components inside a host cell, effectively turning the cell into a virus factory.

Viral Replication

Understanding the Viral Lifecycle

Viruses are unique entities in biology because they're not truly alive by standard definitions–they can't reproduce without a host. During viral replication, a virus attaches to a host cell and injects its genetic material into it. In the case of RNA viruses that act as mRNA, their single-stranded RNA genome immediately interacts with the host's ribosomes to begin synthesizing proteins essential for the virus lifecycle.

Unlike DNA viruses that need to enter the nucleus and use the host's DNA-dependent RNA polymerase to create mRNA, these mRNA viruses save crucial time and commence replication promptly. Speed is critical in viral replication because the faster a virus can produce progeny, the more likely it is to sustain an infection and avoid the host's immune defenses. The simplicity and speed afforded by mRNA virus genomes is a stark advantage in the ruthless world of microbial competition and survival.

Gene Expression

From DNA to Functional Proteins

Gene expression is the multistep process by which information from a gene is used to construct a functional product like a protein. It involves two main stages: transcription, where DNA is converted into RNA, and translation, where RNA is translated to build proteins. The role of mRNA in this process is pivotal as it bridges the gap between the genetic code in DNA and the amino acid sequence of proteins.

In the context of viral infection, a virus with an mRNA genome sidesteps the initial transcription phase, accelerating the gene expression process to favor its multiplication. This rapid gene expression allows such viruses to quickly exploit the host's machinery, leading to faster synthesis of viral components and enabling the virus to take over the cell before the immune system can mount an effective response. It's a clever evolutionary strategy that gives mRNA viruses a replication edge over other viruses that require a more complex process to express their genes.