Biology 1001A Lecture Notes - Lecture 2: Red Algae, Green Sulfur Bacteria, Cyanobacteria

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BIO 1001A - Lecture 2 - Evolution in Action: Human Immunodeficiency Virus
Reminder: Lecture Cycles
Today’s lecture on HIV
Sometime between Wednesday and Monday there will be a guided study assignment
Section 001 meets Mon and Wed, section 002 Tuesdays and Thursdays
Can come to either class, but the quizzes must be taken with your section
Beth’s Office Hours
Start next week
Mondays & Thursdays: 12-1, BGS 3046
No appointment needed, just show up
Can also post questions on OWL forums
Where do viruses fit in the tree of life?
We humans are more closely related to archaea than bacteria
However, all organisms are related to one common ancestor
However, viruses don’t belong in the tree of life
Viruses can’t reproduce without host cells, don’t have their own metabolism, aren’t
cellular based and therefore are not living organisms
Viruses can evolve as organisms can evolve
Evolutionary Origins of Viruses
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We don’t know exactly where they are from
One theory is that they are the descendants of a cellular ancestor
A cellular organism LOST independent metabolism
Another idea is that mobile genetic elements (RNA or DNA) elements GAINED ability to
enter/exit cells
Another theory is that viruses are more ancient than cellular life
Unknown if there is a single origin or many different tactics
Harder to design safe antiviral drugs than antibiotics
Viruses are obligate intracellular parasites
Viruses have different physiology from bacteria (ex. no cell wall)
The virus uses the host cell to reproduce, so anything done to interfere with viral
replication would kill the host cell in turn
Viruses don’t have their own metabolism or unique steps that can be used to target with
drugs as bacteria does
Good News & Bad News About Retroviruses (e.g. HIV)
Central dogma of molecular biology, what is commonly occurring
DNA (replication) → RNA (transcription) → Protein (translation)
HIV and other retroviruses have an RNA genome, so they have to go through an extra
stage in reproduction and disobey the central dogma of molecular biology
RNA (reverse transcription - no proofreading) → DNA (replication in host cell)
RNA (transcription) → Protein (translation)
Since viruses have no proofreading enzymes, mutations are common
In designing antiviral drugs, we can target reverse transcription as it is a stage unique to
viruses and not human host cells
Unfortunately, viruses mutate easily
To minimize side effects of antiviral drugs, attack virus specific steps
Virion enters host cell
Reverse transcriptase → Viral DNA
Integrase splices viral DNA into host DNA
Transcription, translation, protease
New virions assemble, bud or burst out, and enter bloodstream
AZT mimics thymidine and ‘fools’ Reverse Transcriptase
If reverse transcriptase tries to reverse transcript a T nucleoside, it will be fooled by the
drug AZT and pick up AZT instead as it is similar in shape
Once it picks up AZT, reverse transcriptase ceases its process
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