Class Notes (836,580)
Canada (509,856)
Biology (1,140)
BIOL 1004 (106)

generations of HIV

3 Pages
Unlock Document

BIOL 1004
Tamy Superle

o Because thousands of generations of HIV replication take place within each patient during the course of an infection, a single strain of HIV can produce hundreds of different reverse transcriptase variants over time  Because of their large numbers, it is a virtual certainty that one or more of these variants contains an amino acid substitution that lessens reverse transcriptase’s affinity for AZT o If the patient takes AZT, replication of unaltered HIV variants is suppressed, but the resistant mutants will still be able to synthesize some DNA and produce new virions o As the resistant virions reproduce and the non-resistant virions fail to propagate, the fraction of the virions in the patient’s body that are resistant to AZT increases over time  Furthermore, each new generation in the viral population is likely to contain virions with additional new mutations  Some of these additional mutations may further enhance the ability of reverse transcriptase to function in the presence of AZT  Because they reproduce faster, the virions that carry these new mutations will also increase in frequency at the expense of their less- resistant contemporaries  Process of change over time in the composition of the viral population is called evolution by natural selection  Changes in the genetic makeup of HIV populations over time have led to increased drug resistance. This is an example of evolution by natural selection.  When AZT therapy has been stopped, proportion of AZT-resistant virions in the viral population has fallen back toward what it was before AZT treatment began.  Back-mutations that restored reverse transcriptase’s amino acid sequence to its original configuration became common because the virons that carried them out-reproduced AZT- resistant forms  The viral strain that increases in frequency is the one that replicates fastest in the current environment o Without AZT present, natural selection favours nonmutant virions; with AZT present, natural selection favours mutant virions o Is evolution by natural selection unidirectional and irreversible? HELL NO!  Heritable traits that lead to survival and reproductive abundance spread in populations; heritable traits that lead to reproductive deficit disappear. This is evolution by natural selection. 1.1-Why is HIV Fatal?  The idea that evolution by natural selection, is an automatic process that simply happens whenever a population shows the necessary heritable variation in survival and reproductive success o Traits conducive to surviving and reproducing spread throughout the population; traits conducive to dying without issue disappear Short-Sighted Evolution  If there is a resistant to HIV and Aids, then we can expect that resistance will spread throughout the human population as generations pass  Antibodies and killer T cells recognize HIV and HIV-infected cells by binding to epitopes- short pieces of viral protein displayed on the surface of the virion or the infected cell o These epitopes are encoded in HIV’s genes  Mutations in the genes can change the epitopes and may enable the mutant virion to evade
More Less

Related notes for BIOL 1004

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.