Dr. Reichler’s Bio 212  MW10-11am    Print Name:_______KEY_____________
Exam #2   March 5, 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 don’t 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. You were originally a single cell, now you are made of trillions of cells.  How are different types of cells formed from virtually identical DNA?
Differences in gene expression

2. a. What is one difference between signal transduction via steroids and other forms of signal transduction?
Any one of:  The receptor is inside the cell.  The signal enters the cell.  The receptor/steroid complex works directly to change gene expression.  There is little amplification of the signal.

b. How can the same signal give different responses in different cells?
Any one of:  Different receptors may lead to different responses.  Different effectors/relay molecules may lead to different responses.

3. a.  Why are additions or deletions of nucleotides often more damaging to the protein produced than simply changing a nucleotide?
They change the reading frame.  Codons are 3 nucleotides.  Adding or deleting a nucleotide will change the whole sequence.

b. Within a gene, could a change of nucleotides occur without causing a change to the protein produced?  Explain.
Yes. (Any one of)  it could be in an intron, which is spliced out.  Most amino acids are coded for by multiple codons, so a change might not change the amino acid.  It could be in the promoter or terminator, which do not directly code for the amino acids.

4. a.  Given this bacterial DNA double helix, show the RNA that would be produced.  Also label the 5’ and 3’ ends of the RNA.  (5 pts)
Terminator    3’-ACGTACGTGCAT-5’    Promoter
Terminator    5’-TGCATGCACGTA-3’    Promoter


b. What are two differences between transcription in prokaryotic and eukaryotic cells?
Any two of:    Pro-  have operons, no introns, RNA polymerase binds directly to promoter, transcription occurring simultaneously with translation
        Euk-  each coding region has its own promoter/terminator (no introns), has introns, RNA polymerase needs transcription factors to bind to promoter, transcription and translation occur separately

c. In eukaryotic cells what three things happen to an mRNA between transcription and transport to the cytoplasm, and what is the function of each these steps?
5’ cap added- stabilizes mRNA or signal for ribosome binding.  3’ poly-A tail- stabilizes mRNA or signal for transport to cytoplasm.  Introns removed- splicing of exons to get correct reading frame.

5. a.  A tRNA has two ends.  What is the function of each end?
One end has anticodon of mRNA, other has amino acid bound to it.

b. What purpose do the parts of the mRNA outside of the coding region serve?
Control stability of the mRNA, and allow for regulation/blocking of translation

6. a.  The cell needs ten thousand copies of Workinglikeadog, a protein.  There is only one gene for Workinglikeadog in the genome.  What processes in the cell allow for the production of such large quantities of a single protein?
Multiple transcription of the gene and/or then multiple translation of each mRNA

b. How might the cell regulate the expression of Workinglikeadog if it is needed very quickly?
Any one of:  Make the mRNA, but block translation until it is needed.  Make an inactive protein, and activate it when needed.
c. What two processes could the cell use to control the quantity of Workinglikeadog if it is not a protein, but instead active as RNA?
Regulate transcription.  Control stability of RNA.

7. When a virus invades a cell, it often changes the gene expression of the cell.
a. What three cellular genes might the virus cause to be expressed in the cell?  (3 pts)
Any three gene products that are involved in DNA replication or gene expression such as:  DNA polymerase, helicase, primase, ligase, RNA polymerase, ribosomal RNA or proteins, tRNA, aminoacyly synthetase…(do not need to give a name, if they describe the gene product)

b. Why might the virus cause these cellular genes to be expressed?
To increase DNA replication and protein production so that more viruses can be made

c. How might the virus cause changes in the expression of these cellular genes?
Any one of:  Mimic a signal that would increase the expression of these genes.  Increase transcription of the genes.  Decrease breakdown of the mRNA or proteins.

8. A single gene leads to a single type of protein.  Disprove this statement with evidence from prokaryotic and eukaryotic cells.
Pro-  have operons which use a single promoter/terminator to produce multiple proteins.  Euk-  Alternative splicing can cause different proteins to be produced from one gene.

Bonus:  Virtually every organism on earth uses the same genetic code.  What does this say about life?  (3 pts)
Many possible answers…One single origin of life