In reality, viruses may have evolved in any of these ways.
Three competing theories try to explain the origin of viruses. Scientists use molecular techniques to compare the DNA and RNA of viruses and find out more about where they come from.
Viruses do not leave fossil remains, so they are difficult to trace through time. Just as there are friendly bacteria in the intestines that are essential to gut health, humans may also carry friendly viruses that help protect against dangerous bacteria, including Escherichia coli. Seven coronaviruses can affect humans, but each one can change or mutate, producing many variants. It also has an envelope with crown-like spikes on its surface. A coronavirus, for example, has a sphere-like shape and a helical capsid containing RNA. Within these categories are different types of viruses. whether or not they have a protective lipid envelope derived from the host cellĮxamples of viruses with an envelope include the influenza virus and HIV.the type of their nucleic acid, which contains their genetic information.their shape and size, which may be rod-shaped, almost spherical, or other shapes.Scientists categorize viruses according to various factors, including: Next, the virus continues to reproduce, but it produces more viral protein and genetic material instead of the usual products that the cell would produce. It uses the host’s cellular machinery to make many copies of itself. This makes them unable to reproduce independently and totally dependent on their host.Īfter entering a host cell, a virus hijacks the cell by releasing its own genetic material and proteins into the host. They also do not contain ribosomes, so they cannot make proteins. They can grow and reproduce, but they do not produce adenosine triphosphate, a compound that drives many processes in living cells. There is some dispute about whether viruses meet the criteria for living organisms. There, if the conditions are right, they can multiply. These spikes are proteins that enable viruses to bind to and enter host cells. The core is covered with a capsid, a protective coat made of protein.Īround the capsid, there may be a spiky covering known as the envelope. Viruses are microscopic entities that have a core of genetic material, either DNA or RNA. The spherical viral particles, colored blue, contain a cross-section of the viral genome, in the form of black dots. Share on Pinterest API/Gamma-Rapho via Getty Images Electron microscope image of the first U.S. In this article, we discuss in detail viruses, including how they act and how they can affect people. This may be spiky and helps them latch onto and enter host cells. Some have an additional coat called the envelope. They consist of genetic material, DNA or RNA, with a coat of protein around it. This explains why a virus that causes illness in a cat may not affect a human. For example, severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2, causes the disease COVID-19.Ī virus may also affect one organism in one way but a different one in another. Viruses are biological entities that can only thrive and multiply in a host, which is a living organism such as a human, an animal, or a plant. They are present in animals, plants, and other living organisms, and they can sometimes cause diseases. Viruses are microscopic particles that exist almost everywhere on Earth.
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