Dr. Reichlerıs Bio 212  MWF 2-3pm          Print Name:______________KEY__________

Exam #2   Oct. 16, 2003


            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.     Even after billions of dollars and many years of research we still do not have extremely effective treatments for viral infections.  What are two reasons that viral diseases are difficult to treat?  (8pts)

Any two of:  viruses replicate inside cells, viruses can enter the lysogenic cycle, they use the same biological molecules as humans


2.     What are three processes occurring inside cells that can cause mutations, and how does each one affect the DNA?

Any three of:  replication errors- change single nucleotides, transposons- large insertion of DNA, lysogenic virus- large insertion of DNA, environment (UV, toxins)- small changes to nucleotides


3.     Why are both DNA and proteins poor candidates for the first biological molecule?

DNA does not have enzymatic activity.  Proteins are not replicatable.


4.     The experiment to test the ability of RNA to self-ligate was repeated several times.  Each time the ability of RNA self-ligation increased.  Why?

Successful ligating RNA bound to the column and were selected for subsequent experiments


5.     Why do transposons need gene expression to move?

Transposons need either the proteins transposase and/or reverse transcriptase to be expressed so they can move.


6.     What gene would be expressed in all human cells?  Why would this gene be expressed in all human cells?  (8pts)

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,


7.     What gene would be expressed only in some human cells, what type of cell (by name or description) would be expressing this gene, and why is this gene expressed in this cell type and not in others?  Explain.  (8pts)

Many answers, only one is needed:  DNA polymerase-only cells replicating the DNA need this protein, telomerase-only cells going through a lot of mitosis/DNA replication need this, hemoglobin-only red blood cells make this. Insulin/glucagons-only some pancreatic cells respond to blood sugar levels


8.     Is all of the DNA in a cell packaged to the same extent at any moment?  Why or why not?

No, expressed genes are unpackaged.  Genes that are not needed are tightly packaged.


9.     How can the expression of one gene affect the expression of another gene?

Most factors controlling gene expression, RNA polymerase/transcription factors/histones/splicesomes/etc, are themselves proteins and must be expressed.


10.  How could an organism with 5,000 genes produce 6,000 different types of gene products?

Alternate splicing could cause some of the genes to produce multiple proteins.


11.  Describe how three processes during gene expression would occur to ensure high quantities of a single protein were produced.

Any three of:  Enhancers increasing transcription, transcription factors increasing transcription, increased mRNA stability, increased protein stability


12.  What are two similarities and two differences between gene expression and DNA replication?  (8pts)

Any two:  similar- base pairs used, DNA read 3ı->5ı, start at definite sites, proteins involved, DNA unwound,

Differences- gene express: only uses part of DNA, reads one strand, starts and ends and definite sites, RNA polymerase,

                        DNA rep: uses all of DNA, reads both strands, starts at definite site but ends when finished, DNA polymerase,


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

Original strand- H bonds broken, covalent unaffected.  New strand- new H bonds formed, new covalent bonds formed.


14.  During DNA replication, why does the lagging strand use several DNA ligases while the leading strand uses only one?

Leading strand follows helicase unwinding, and only one primer is used.  Ligase covalently binds the DNA replacing the RNA primer and the subsequent DNA.  Lagging strand is replicated away from the unwinding helicase in short pieces.  DNA poly starts multiple times using multiple primers and therefore multiple ligases.


15.  What are two reasons that replicated human DNA is slightly different from the original DNA, and how do cells minimize these differences?  (8pts)

There are some replication errors, and the DNA is slightly shorter.  DNA repair minimizes errors, Telomeres ensure that lost DNA is not genes and limit total number of replications.



Bonus:  Symptoms from a bacterial infection often are not apparent until a few days after the infection.  Why?  (3pts)

Bacteria initially enter a lag phase while they acclimate to the environment, then grow exponentially.