Immune System
What is a Virus?
https://www.youtube.com/watch?v=L8oHs7G_syI
A virus is a non-living obligate parasite made up of nucleic acids (single-stranded or double-stranded linear RNA or DNA) and a protein capsid. Viruses can also contain other macro-molecules like carbohydrates and lipids which they derive from host cells. An obligate parasite is a parasite that requires a living host in order to reproduce. Although viruses can exist outside of a host cell they can only reproduce using host machinery (organelles, enzymes, and monomers produced by the host cell) to replicate inside the cell which is why they are considered non-living. An individual virus or viral particle is known as a virion (viral equivalent of a cell).
How do Viruses Infect Cells?
Viruses infect host cells in order to replicate. First, the virus has to infect the cell. Viruses exploit endocytic pathways in the cell in order for the viral capsid including the genetic material to enter the cell. Once inside, the capsid is disassembled to release the genetic material into the host cell. The viral genome then directs the synthesis of more viral particles. These new virions don't need an envelope, and they are released by rupturing the host cell's plasma membrane, which kills the cell. Enveloped virions can get it by passing through a portion of the plasma membrane that has viral recognition proteins attached and budding out of the cell, which usually doesn't injure the cell or break the membrane.
VIrus Infecting A Cell
HOw Does the Human IMmune System Respond to Viral InFections?
The immune system has three lines of defense against invading pathogens. The first line of defense in non-specific barriers, barriers that attempt to protect the outer layer of the body from pathogens like viruses. These non-specific barriers are chemical and physical and include the skin, earwax, mucous membranes, saliva, and stomach acid.
When this first line of defense is penetrated, the second line of defense, white blood cells, attempt to inhibit or destroy pathogens before they harm the body. In particular, viruses and virus-infected cells stimulate Beta lymphocytes to produce antibodies.
If the virus gets past the first two non-specific defenses, then the body has a third line of defense, which is the specific immune response. This specific immune response is carried out by antibodies, y-shaped proteins that bind to pathogens to inhibit their ability to reproduce inside a host cell. Antibodies can actually work in multiple ways. They can work together to cause viral particles to stick in a process called agglutination and they can also trigger phagocytosis where the cell engulfs and destroys the virus.
There are also other immune responses to viral infection. Virally infected cells can produce small proteins called interferons that prevent viruses from replicating.