STAT 2230 Chapter Notes - Chapter 1: Mutation Rate, Azide, Cubic Metre

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28 Jan 2013

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Chapter 1- Understanding HIV
Why study evolution?
oThe tools and techniques of evolutionary biology offer crucial insights into matters of life and death
Human Immunodeficiency Virus (HIV) causes Acquired Immune Deficiency Syndrome (AIDS)
oHIV is an emerging virus, it rapidly evolves drug resistance and it is deadly
Evolutionary biology is the science devoted to understanding two things:
oHow populations change through time following modifications in their environment
oHow new species come into being
1.1- The Natural History of the HIV/AIDS Epidemic
List of worst epidemic in human history according to the number of deaths:
oInfluenza-50 to 100 million deaths-across the globe
oBlack Death (1347-1352)-took 30%-50% of the European population-about25 million lives
oNew World small pox-released in 1520 by European conquistadores-decimated Native American
populations across two continents
AIDS is among the worst epidemics in human history
oWas first recognized in 1981
oSo far infected more than 65 million people
o25 million have already died
oBy year 2020, a total of 90 million lives would have been claimed by AIDS
oAccording to World Health Organization, AIDS is responsible for about 4.9% of all deaths worldwide
oSub-Saharan Africa is mostly affected by this epidemic
HIV establishes a new infection when a bodily fluid holding the virus, usually a blood or semen, carries it
from an infected person directly onto a mucous membrane or into the bloodstream of an uninfected person
oCan be passed during heterosexual sex, homosexual sex, oral sex, needle sharing, transfusion with
contaminated blood products, childbirth, and breastfeeding
An HIV infection can be acquired only from someone else who already has it!
What is HIV?
Like all viruses, HIV is an intracellular parasite that cannot reproduce on its own
oIt invades specific types of cells in the human immune system
oIt uses enzymatic machinery and energy of these cells to make copies of itself, killing the host cells
in the process
Figure 1.5 (Pg. 7) contains the life cycle of HIV in detail.
oThe life cycle includes an extracellular phase and an intracellular phase
oDuring the extracellular phase, the virus moves from one host cell to another, and can be
transmitted from host to host
oExtracellular form of a virus is called a virion, or virus particle
oDuring intracellular or parasitic phase, the virus replicates
HIV initiates its replication phase by latching onto two proteins on the surface of a host cell
HIV binds to two surface proteins on the target cell called CD4 and coreceptor
This binding fuses the virion’s envelope with the host’s cell membrane and spills the contents
of the virion into the cell
These contents include the virus’s diploid genome (two copies of a single-stranded
RNA molecule) and 3 proteins:
oReverse transcriptase- transcribes the virus’s RNA genome into DNA
oIntegrase- splices the DNA genome into the host cell’s genome
oProtease- which plays a role in the preparation of new viral proteins
In HIV and other retroviruses, flow of genetic information is different than in cells and
in viruses with DNA genomes
In retroviruses, genetic information does not follow the familiar route from DNA to
mRNA to proteins
oInstead it flows from RNA to DNA, then to mRNA to proteins
Once HIV’s genome is inserted into the host cell’s chromosomes, the host cell’s RNA
polymerase transcribes the viral genome into mRNA, and the host cell’s ribosomes synthesize
viral proteins
New virions assemble in the host cell cytoplasm, then bud off the cell membrane and
enter the bloodstream
There, the new virions may find another cell to infect in the same host, or be
transported to a new host
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