1/13/2024 0 Comments Coursenotes ap biologyThe first line of defense includes epithelial cells and mucus membranes. This includes lymphocytes and antibodies, more specific to definitive types of invaders. The third and last line of defense is what’s typically referred to as the immune system. This would include phagocytic white blood cells. The second is non-specific, as well, but internal. The first lines of defense are physical barriers such as skin and mucus membranes. There are three general lines of defense the body has against invaders. Viruses can generally only be prevented with vaccines, though bacteria can be cured with antibiotics. They may lean more heavily to one side, as in the flu virus, which exists mostly in a lytic phase. Most viruses are actually a bit of both, part lysogenic, part lytic. Occasionally, there may be a stimulus that drives it out of the chromosome and into a lytic cycle. It’s dormant, and when the cells divide, the DNA from the virus also divides and is copied. When a virus becomes part of the chromosomes, the virus DNA in there is called prophage. It attached to a host cell, injects its DNA (or if it uses RNA, then it undergoes reverse transcription to have DNA available), and then the lytic cycle turns off the cell’s machinery and forces it to make proteins for the virus. The flu is an example of this type of virus. There is a lytic phase to many viruses in which they copy themselves and then destroy the host cell before moving on to other cells in the body. To lyse something is essentially to cut it up, or destroy it. Lysogenic virus DNA hides in your chromosomes and generally remains dormant. Viruses have a capsid (protein code) and inside this is DNA or RNA. They are no considered to be alive, yet do take great strides to replicate themselves. They need energy from their environment, as they can’t maintain an internal stable environment on their own. Viruses have been a topic for discussion over a long time as they are rather unique in both their structure and function. Your body can be attacked from within, whether by mutated cells, or more often, viruses or bacteria. Let’s take a closer look at the workings of the immune system as far as what you’ll want to know for the AP® Biology exam. So our immune system is there to help keep us safe. Our cells have no walls, as we traded in mobility for susceptibility over the course of evolution. Animals must defend themselves against viruses, bacteria, and other types of intruders. What do you think of when you hear “immune system?” Maybe your body fighting a cold, maybe white blood cells? Your body’s immune system is there to protect you, both from inside and outer-body offenses.
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