BIOL 100 Chapter Notes - Chapter 43: T Helper Cell, Immunodeficiency, Reverse Transcriptase
Textbook Notes
Chapter 43
HIV/AIDS
Concept 1: How it Works
How It Works
HIV/AIDS has become a pandemic which means it has spread all over the world
The HIV virus causes a collapse of the immune system (immune deficiency) and the final stage of this condition
is known as AIDS
Viruses - microscopic parasites that can reproduce only inside a host cell
Some consider viruses to be amazing cellular “terrorists” since they infect and kill the host cell by taking
over the molecular machinery in the infected cells
Can infect all types of organisms
Retrovirus - it is a virus with an RNA genome that uses reverse transcriptase to make. DNA copy of its RNA
genome
This DNA copy of the genome is then integrated into the host cell's DNA
Lentivirus - biological properties that are responsible for illnesses of long-duration which have a long incubation
period
Symptoms of the disease may not become evident for years after the initial infection
Glycoproteins (gp120 and gp41) - allow the HIV virus to attach to and penetrate into the host cell with the aid of
a second protein found on the target cells
Reverse transcriptase - synthesize DNA, using the HIV RNA genome as a template after host cell infection has
occurred
Steps in the HIV replication cycle:
Fusion of HIV to the host cell surface
HIV RNA, reverse transcriptase, integrate, and other viral proteins enter the host cell
Viral DNA is formed by reverse transcription
Viral DNA is transcriported across the nucleus and integrates into the host DNA
New viral RNA is used as genomic RNA and to make viral protein
New viral RNA and proteins move to the cell surface and a new immature, HIV forms
The virus matures by protease releasing individual HIV proteins
Concept 2: Early Stages of HIV Infection
Early Stages of HIV Infection
Stage 1: primary HIV infection, lasts for a few weeks
This stage of infection is sometimes accompanied by a short flu-like illness and enlarged lymph glands
There is a large amount of HIV in the peripheral blood and the immune system begins to respond to the
virus by producing HIV antibodies (seroconversion) and cytotoxic lymphocytes (CD8+ T cells)
Stage 2: clinically asymptomatic stage, lasts for an average of ten years
The level of HIV in the peripheral blood drops to very low levels but people remain infectious and HIV
antibodies are detectable in the blood
The HIV virus infects and kills 'Helper' T cells (CD4 T cells), an important part of the immune system
This leaves the host (HIV+ patient) with an immune system that becomes ineffective due to the inability