Dr. Reichlerıs Bio 212  MW 9-10am             Print Name:______________KEY___________

Exam #2   March 10, 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 donıt 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.       Prairie voles and montane voles both have the same oxytocin and vasopressin receptors in their brains.  What is different about the DNA of these voles so that the same protein is produced in different quantities?  (8pts)

Any of:  Differences in the promoter so one is transcribed more than the other.  Diffferences in the UTR so that translation is blocked or the mRNA is degraded more rapidly.



2.      If a person was resistant to HIV (the virus that causes AIDS) because the virus cannot enter the cell, what might be different about this personıs DNA to make them resistant to HIV?

The membrane protein that the viruses uses to enter the cell is missing,  non-functional, not located to the membrane, or different enough so that HIV cannot recognize it



3.      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 uses RNA as its genetic component so it must be made into DNA by RT for the virus to replicate.



4.      What limits viral growth?

Availability of cells to infect



5.      What lessons about human population growth can we learn from bacteria?

Eventually we will run out of resources and build up too many waste products, and our population will level out.



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

The repressor for the trp operon is activated to inhibit transcription by binding to tryptophan.



7.      Once introns are removed from a human gene, what other change would be necessary for the human gene to be expressed in bacteria?

Changing the promoter to a bacterial one.  In bacteria RNA poly binds directly to the promoter.  In Euk transcription factors are needed for RNA poly to bind.



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

Operons and Alternate Splicing



9.      Give two examples of genes, whose products control the expression of one or more other genes.  (8pts)

Any two of:  repressors in bacteria, transcription factors, splicing enzymes, proteins controlling RNA or protein degradation (ubiquitin)



10.   Would the methylation of a gene result in a decrease in the amount of the protein produced by that gene?  Why or why not?  (8pts)

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.



11.   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.



12.   Describe a gene that would be expressed only in some human cells?  Why would this gene be expressed in some human cells and not others?  (8pts)

Many answers such as:  Primase, helicase, DNA polymerase, ligase- all needed only during DNA replication.  Insulin, glucagon- only produced in cells sensitive to sugar levels



13.   How is DNA packaged at the origin of replication during DNA replication?  Why?

The DNA would need to be unpackaged so that the helicase and other proteins can access the DNA.



14.   During DNA replication, what is happening to the hydrogen bonds and covalent bonds on both the original (template) and new DNA strand?  (8pts)

H-bonds are breaking between original strands and forming between original strand and incoming nucleotides.  Covalent bonds are being formed between new nucleotides.



15.   If primase were not functioning, what would be the effect on DNA replication?  What would and would not occur?

The DNA wound unwind.  DNA polymerase would not be able to start copying the DNA.




Bonus:  What connections do scientists hypothesize for birth order, birth weight, and sexuality?  (3pts)

Each son that a woman has increases the motherıs immune reaction to the  uniquely male proteins in the male fetus.  This leads to lower birth weight for later born sons and possibly a lack of development of some masculine characteristics which leads to a greater chance of homosexuality.