Dr. ReichlerÕs Bio 325          TTh 12:30-2pm           Print Name:___________KEY_____________

Exam #2   March 11, 2004


            Answer each question as succinctly as possible in the space provided.  If needed, continue on the back.  If you use a drawing as part of your answer, be sure to also include a written explanation.  Read each question carefully and donÕt hesitate to ask if a question seems unclear.  These questions have specific answers, although for some, more than one answer is possible.  To receive full credit you must clearly and fully answer the question being asked.  Each question is worth 6 pts, unless otherwise noted, for a total of 103 points possible for this exam.


1.     What limits viral growth?

The availability of cells to infect.



2.     Generally viruses use cellular components to replicate.  What strictly viral component does HIV need to replicate in a human cell?  Why is this viral component critical for HIV replication?

Reverse transcriptase, HIV has RNA, it needs to use RT to go from RNA to DNA so it can make more virus RNA and proteins or integrate the DNA into the host cell DNA.



3.     When studying T-cell activation by HIV infection:  (see figure)


a.  Why was IL-2 (interleukin-2) measured?

The experiment is testing whether HIV infection activates T-cells,

IL-2 is produced by T-cells when they become activated.

b.  What conclusion can be reached from the results with T-cells infected by HIV and treated with AZT?  How does the data lead to this conclusion?

The virus must be making some gene product to activate the T-cells because AZT inhibits HIV gene expression by inhibiting reverse transcriptase, and AZT blocks T-cell activation by HIV.



4.     If HIV has perfect replication fidelity, can someone infected by drug-susceptible virus develop resistant viruses?  Why or why not?

No, mutations must occur for some of the HIV to become resistant.



5.     Influenza (the virus that causes the flu) can regulate transcription and translation separately, but bacteria typically cannot.  Why?

Influenza is infecting a eukaryotic cell and uses the eukaryotic gene expression mechanisms.  In bacteria there is no separation of the DNA from the cytoplasm so transcription and translation are occurring simultaneously.



6.     Describe a post-translational modification of a protein in bacteria.  What is modified, and what is the effect of that modification?

The trp operon repressor is activated by the presence of tryptophan which blocks transcription of the trp operon.



7.     What can we learn about human population growth from studying bacteria?  (4 pts)

Eventually we will run out of resources or build up too many waste products and our population increase will stop.



8.     Is copy fidelity more important for memes or genes?  Why?

Genes.  Poorly copied memes can still be transmitted, but mutations in genes are often fatal.



9.     Describe a gene that would be expressed in all human cells?  Why do all human cells need to express this gene?

Many answers, only one is needed:  Histones-all cells have DNA that needs to be packaged, RNA polymerase- all cells are transcribing, tRNA or ribosomes-all cells are translating, splicesome-all cells need to remove introns, snRNA-involved in splicing



10.  Give two examples of a single promoter controlling the production of multiple proteins.

Operons and Alternate Splicing



11.  Give three examples of genes, whose products control the expression of one or more other genes.

Any three of:  microRNA, repressors in bacteria, transcription factors, splicing enzymes, proteins controlling RNA or protein degradation



12.  Would the methylation of a gene cause a decrease in the amount of the protein produced by that gene?  Why or why not?

Either:  Yes, methylation would stop transcription and eventually the previously produced protein would be degraded.

No, even if transcription stops, the protein or mRNA might be stable.



13.  Fibrin is a protein involved in blood clotting.  During blood clotting, would changes in the transcription of the fibrin gene occur?  Why or why not?

Either:  No, the change occurs post-translationally.

Yes, more is needed to replace what was used to clot the blood.



14.  Describe three processes during gene expression that would ensure production of high quantities of a single protein.

Any three of:  Acetylation of nearby histones, Demthylation of the DNA, Enhancers increasing transcription, transcription factors increasing transcription, increased mRNA stability, increased protein stability



15.  How do microRNAs affect gene expression?

By binding to the 3ÕUTR of mRNA and inhibiting translation.



16.  If you were searching for putative microRNA genes in human DNA, what would you look for?

Small regions of DNA with complementary sequences within the same strand.




Bonus:  In chapter 10 of Nature via Nurture, what hypotheses do scientists propose to explain the human propensity for classifying people by race?  What experiment did they do to test their hypotheses?  (3 pts)

Race is a key for what group you belong to.  Historically there was less variation in skin color, but it was still important to identify coalition membership.  Researchers asked people to match photos to quotes and looked for mistakes in correct matches.  When given quotes from various people of the same skin color, mistakes were commonly made.  But when there was an alternate obvious coalition membership, people made mistakes by coalition and ignored skin color.