How are virus made

Viruses generally come in two forms: rods or spheres. However, bacteriophages viruses that infect bacteria have a unique shape, with a geometric head and filamentous tail fibers. No matter the shape, all viruses consist of genetic material DNA or RNA and have an outer protein shell, known as a capsid. There are two processes used by viruses to replicate: the lytic cycle and lysogenic cycle. Some viruses reproduce using both methods, while others only use the lytic cycle.

In the lytic cycle, the virus attaches to the host cell and injects its DNA. Then fully formed viruses assemble. These viruses break, or lyse, the cell and spread to other cells to continue the cycle. Like the lytic cycle, in the lysogenic cycle the virus attaches to the host cell and injects its DNA.

In humans, viruses can cause many diseases. For example, the flu is caused by the influenza virus. Typically, viruses cause an immune response in the host, and this kills the virus. However, some viruses are not successfully treated by the immune system, such as human immunodeficiency virus, or HIV. This leads to a more chronic infection that is difficult or impossible to cure; often only the symptoms can be treated.

Unlike bacterial infections, antibiotics are ineffective at treating viral infections. Viral infections are best prevented by vaccines, though antiviral drugs can treat some viral infections. Most antiviral drugs work by interfering with viral replication. Some of these drugs stop DNA synthesis, preventing the virus from replicating. Although viruses can have devastating health consequences, they also have important technological applications. Viruses are particularly vital to gene therapy.

Because some viruses incorporate their DNA into host DNA, they can be genetically modified to carry genes that would benefit the host. Some viruses can even be engineered to reproduce in cancer cells and trigger the immune system to kill those harmful cells. Although this is still an emerging field of research, it gives viruses the potential to one day do more good than harm.

Antibiotics do not stop viruses. There are three classical hypotheses but many new ideas and discoveries challenging them. The first one is the virus first hypothesis , and states that since viruses are so much simpler than a cell, they must have evolved first, and that ancestors of modern viruses could have provided raw material for the development of cellular life. The key data that supports this is apparent when you look at virus genes, compare them and their genetic sequence with cellular life data available in genetic databases.

This model also suggests there was an ancient virosphere from which all viruses evolved. However, some scientists dismiss this hypothesis because of one key feature. So, how could viruses have survived before the existence of cellular life? The second model is called the regressive hypothesis, sometimes also called the degeneracy hypothesis or reduction hypothesis. This one suggests that viruses were once small cells that parasitized larger cells, and that over time the genes not required by their parasitism were lost.

The discovery of giant viruses that had similar genetic material to parasitic bacteria supported this idea. The third model is escape hypothesis , or vagrancy hypothesis , and states that viruses evolved from bits of RNA or DNA that escaped from genes of larger organisms.

For example, bacteriophages viruses that infect bacteria came from bits of bacterial genetic materials, or eukaryotic viruses are from bits of genetic material from eukaryotes like us. However, in this model, it would be expected that viral proteins would then share more qualities with their hosts, but this is largely not the case.

Some recent discoveries of giant viruses have even further complicated the question about the origin of viruses.

These discoveries also challenge many of the classical definitions of what makes a virus, such as the size requirement, gene behavior, and how they replicate. Giant viruses were first described in Mimiviruses are different from viruses in that they have way more genes than other viruses, including genes with the ability to replicate and repair DNA.

The pandoravirus, discovered in , is even larger than the mimivirus and has approximately genes, with 93 percent of their genes not known from any other microbe. These sugar-protein complexes are found on the surface of a virus particle, and are called glycoproteins.

While glycoproteins are not specific to viruses there are many examples of glycoproteins throughout all life , they do provide a way for viruses to attach themselves to host cells. Since viral glycoproteins are one of the key ways viruses can infect cells, many scientists are working on medicines that can impact how the glycoproteins work in order to prevent viral illnesses in people, pets, and plants.

In addition to being varied in their shapes and sizes, viruses also demonstrate diversity when it comes to their nucleic acid genomes. The primary function of a viral genome is to store the instructions for building more virus particles.

Regardless of which type of genome a virus has, there are two main routes for packing it: viruses can either assemble their capsid shell around their nuclear genome, or viruses can make a capsid shell, and insert their nuclear genome into it. Viruses also need to make sure that they are packaging their genomes, and not the genomes of their host cells. Because there are millions of different viruses, there are millions of different viral genomes.

So far, scientists have mapped the genomes of 75, viruses, but that is merely a fraction of what is out there. As next generation sequencing and analysis continues to grow in its sophistication, scientists will continue building knowledge when it comes to viral genomes!

Gelderblom, H. Structure and classification of viruses. Baron Ed. University of Texas Medical Branch. Holmes, E. What does virus evolution tell us about virus origins? Journal of Virology, 85 , Knipe, D. Fields virology. Woolhouse, M. Human viruses: discovery and emergence. Update your browser to view this website correctly.