March 27th, 2017
A virus is a tiny particle. Virus particles are about one-millionth of an inch (17 to 300 nanometers) long. Viruses are about a thousand times smaller than bacteria, and bacteria are much smaller than most human cells. Viruses are so small that most cannot be seen with a light microscope, but can only be seen with an electron microscope.
A virus particle consists of three main components. It has nucleic acid, which is a set of genetic instructions, either DNA or RNA, either single-stranded or double-stranded. A virus particle also has a coat of protein, which surrounds the DNA or RNA to protect it. The particle also has a lipid membrane, which surrounds the protein coat (found only in some viruses, including influenza; these types of viruses are called enveloped viruses as opposed to naked viruses).
Viruses vary widely in their shape and complexity. Some look like round popcorn balls, while others have a complicated shape.
Viruses carry only one or two enzymes that decode their genetic instructions. So, a virus must have a host cell (bacteria, plant or animal) in which to live and make more viruses. Outside of a host cell, viruses cannot function.
Viruses lie around our environment waiting for a host cell to come along. They can enter us through the nose, mouth or breaks in the skin. Once the virus is inside the human body, they find a host cell to infect.
Regardless of which type of host cell the virus inhabits, the process of the attack follows the same basic steps known as the lytic cycle. The first step of this cycle is when the virus particle attaches to the host cell. Next the particle releases genetic instructions to the cell, at which point the injected genetic material recruits the host cell’s enzymes to make parts for new virus particles. The new particles then assemble the parts into new viruses. The new particles then break free from the host cell.
Basically, in the lytic cycle, the virus reproduces itself using the host cell's chemical machinery.
Some viruses do not inject their genetic material; instead the simply enter the cell. These viruses have a protein on the outside of their coat that attaches the virus to the membrane of the host cell. Some enveloped viruses can dissolve right through the cell membrane of the host because both the virus envelope and the cell membrane are made of lipids. These viruses that dissolve into a cell simply release their contents once inside the host.
Once inside the cell, the viral enzymes take over the host cell enzymes and begin making copies of the viral genetic instructions and new viral proteins using the virus's genetic instructions and the cell's enzyme machinery. The new copies of the viral genetic instructions are packaged inside the new protein coats to make new viruses.
Once the virus is attacking the human body, the immune system responds to the infection. The human body will begin fighting back, by producing chemicals called pyrogens that cause your body temperature to increase. This fever actually helps you to fight the infection by slowing down the rate of viral reproduction, because most of your body's chemical reactions have an optimal temperature of 98.6 degrees Fahrenheit. If your temperature is higher than that viral reactions slow down. This natural defense continues until the viruses are removed from your body.
Once the new viruses are made, they leave the host cell in one of two ways. They break the host cell open and destroy the host cell. The second option is the viruses pinch out from the cell membrane and break away (budding) with a piece of the cell membrane surrounding them.