Viruses are microscopic particles that exist almost everywhere on Earth. They are present in animals, plants, and other living organisms, and they can sometimes cause diseases.
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. Some viruses cause disease. For example, severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2, causes the disease COVID-19.
A virus may also affect one organism in one way but a different one in another. This explains why a virus that causes illness in a cat may not affect a human.
Viruses vary in form and complexity. They consist of genetic material, DNA or RNA, with a coat of protein around it. Some have an additional coat called the envelope. This may be spiky and helps them latch onto and enter host cells. They can only replicate in a host.
In this article, we discuss in detail viruses, including how they act and how they can affect people.
What are viruses?
Viruses are microscopic entities that have a core of genetic material, either DNA or RNA. The core is covered with a capsid, a protective coat made of protein.
Around the capsid, there may be a spiky covering known as the envelope. These spikes are proteins that enable viruses to bind to and enter host cells. There, if the conditions are right, they can multiply.
There is some disputeTrusted Source about whether viruses meet the criteria for living organisms. They can grow and reproduce, but they do not produce adenosine triphosphate, a compound that drives many processes in living cells.
They also do not contain ribosomes, so they cannot make proteins. This makes them unable to reproduce independently and totally dependent on their host.
After entering a host cell, a virus hijacks the cell by releasing its own genetic material and proteins into the host. It uses the host’s cellular machinery to make many copies of itself.
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.
Viruses have different shapes and sizes. Scientists categorize viruses according to various factors, including:
their shape and size, which may be rod-shaped, almost spherical, or other shapes
the type of their nucleic acid, which contains their genetic information
whether or not they have a protective lipid envelope derived from the host cell