Viruses

A virus is an infectious non-living particle

A virus is only active when inside a living cell. When removed from a living cell, it ceases all activities but retains its ability to infect a cell.

Viruses consist of two parts:

  1. DNA/RNA
  2. Capsid (sometimes has a protective envelope)

Once a virus is inside a host cell, two different processes may occur:

  1. Lytic Cycle
  2. Lysogenic Cycle

Lytic Cycle

In the lytic cycle, a virus enters a cell, makes copies of itself, and & causes the cell to burst. The steps of the lytic cycle are: attach, inject DNA, produce virus genomes and protein capsids, assemble virus DNA/RNA, then cause the cell to burst so all of the viruses are released.

Lysogenic Cycle

In the lysogenic cycle, a virus enters a cell, joins w/ cells DNA, and continues to be a part of each new cell. This does not kill the cell but it lays dormant in the background. The steps of the lysogenic are: attach, penetrate the cell, incorporate its genetic materal, replicate its and the cells genetic material, then cell division.

Sometimes certain environmental conditions can cause a lysogenic cycle to switch to a lytic cycle.

The Immune System

The Immune System has 3 lines of defense

  1. Barriers: Skin, sweat, gastric juice, tears & saliva, mucus, and cilia.
  2. White blood cells, inflammation, and specialized proteins.

The immune system uses white blood cells to defend against pathogens. Some wbcs freely roam the body to destroy pathogens. They are called phagocytes or macrophages. These wbcs destroy pathogens by ingesting them through ‘phagocytosis’ which means cell eating.

A pathogen invasion, like when they enter through a cut or a bite, triggers inflammation. Inflammation results in heat, redness, pain, and swelling. Inflammation assissts in killing the pathogens. Heat raises the temperature.

Once a cell becomes infected by a virus, it releases a specialized protein called interferon. The infected cell may die but interferon stimulates nearby cells to produce antiviral that intereferes with viral replication.

  1. B-Cell Response and T-Cell Response.

B-cells carry only one type of antibody on their surface. It is a specialist for the matching foreign antigen. Once a B-Cell finds the antigen, it is activated and makes millions of identical B-Cells for that one antigen. Once the antibodies bind to the antigen of a foreign invader, they mark it for destrution by another immune cell.

T-cells target infected cells. When a T-Cell detects a pathogen it becomes activated and makes different kinds of T-cells like cytotoxic t-cells which kill infected t-cells and memory t-cells which hlep fight the invader in later infections.

Antigens & Antibodies

Antigens are molecules on the surface of viruses, bacteria, fungi, pollen, and other pathogens.

Antibodies are Y-Shaped proteins that bind to antigens. They are also unique and fit only one type on atigen. Antibodies are found on the surface of certain WBS or freely floating in the blood.

Forms of Immunity

Two natural types of immunity are due to infection by an actual pathogen or due to natural antibodies from mother to infant. Two artifical types of immunity are due to a pathogen in a vaccine or due to antibodies in a passive baccine.