Dr. Reichler╣s Bio 212  MWF 2-3pm          Print Name:__KEY______________________

Exam #1   Sept. 23, 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 100 points possible for this exam.

 

1.     If I want to demonstrate that Bio 212 students who attend discussion sessions get higher grades, and I show that all of the students who attend discussion sessions earn A╣s, have I followed Strong Inference?  Why or why not?  (8 pts)

No, for any one of these reasons, I am using proof, only one hypothesis is presented, and/or the experiment is not done well- maybe all of the students made A╣s.

 

2.     Sometimes DNA is mismatched, an incorrect base pair is created.  How could a cell perceive that the DNA base pair was mismatched?  An example of a mismatch:

GTTAG

CGGTC

The width of mismatched DNA will be either too big or too small.  The 3-D structure of the DNA will be distorted.

 

3.     If a response to a signal involves release of calcium into the cytoplasm, how could you inhibit the cell from responding to this signal?

Either:  block or eliminate the receptor  OR  block the release of calcium by blocking calcium channels  OR  block the action or eliminate calmodulin

 

4.     How could two cells presented with the same signal respond differently?

Either:  different receptors may lead to different signal transduction pathways  OR  different effectors may lead to different responses

 

5.     Given the following prokaryotic DNA double helix, what would the RNA strand be (show the sequence and label the 5╣ and 3╣ ends)?  How many amino acids could be coded for by this mRNA? 3╣ terminator- TCT TCGAAAGTA -promoter 5╣             (8 pts)

5╣ terminator- AGAAGCTTTC AT -promoter 3╣

                                                       3╣UCUUCGAAAGUA-5╣

can code for 4 amino acids.

 

6.     How is the regulation (or control) of transcription different between prokaryotic and eukaryotic cells?

Eukaryotic cells require transcription factors for RNA polymerase to bind to the promoter.  In Prokaryotic cells RNA polymerase binds directly to the promoter unless it is blocked.

 

7.     Why is recognition of the intron/exon border such a critical step in gene expression?

Incorrect splicing at the intron/exon border can lead to frameshift mutations, additional information (amino acids), or loss of information (amino acids).

 

8.     In class I inferred that all of the steps of RNA processing occur simultaneously.  In reality, processing is occurring as the RNA is transcribed.  Given this information, would the 5╣cap or the poly-A tail be added to an mRNA first?

5╣ cap would be added first because RNA is transcribed from 5╣ to 3╣.

 

9.     Would knowing the amino acid sequence of a protein allow you to know the exact sequence of the DNA?  Why or why not?  (8 pts)

No, because (any of these reasons) redundancy in the codons, would not know the sequence of introns.

 

10.  How could a nucleotide substitution make it impossible to form a functional protein?

If the substitution caused a stop codon, the protein translation would stop prematurely.

 

11.  What kind of protein would be least likely to have the amino acid methionine (Met) as the first amino acid?  Why?

A secreted protein would not be likely to have a Met at the beginning because the first several amino acids (the signal peptide) are cut off after translation.

 

12.  While RNA has many of the same functions in eukaryotic and prokaryotic cells, it also functions differently in the two cell types.  Which RNA function is different in eukaryotic and prokaryotic cells?  Explain.

RNA would not be part of the splicesome in Prokaryotic cells because there are no introns to splice.

 

13.  Would a gene from humans be properly expressed in bacteria?  Why or why not?

No, (for any of these reasons) introns would not be spliced; the promoter would not be recognized

 

14.  What would be disadvantageous about having a cell with very little non-gene DNA?

Mutations would be more likely to be in genes and therefore affect the function of the cell.

 

15.  Apply rules 1 and 2 of Strong Inference, to answer the following question:  What is the function of the poly-A tail in RNA?  (10 pts)

Must use Strong Inference and make multiple hypotheses and experiments to eliminate hypotheses.  Ex:  hypo╣s-  The poly-A tail functions to transport RNA out of the nucleus. The poly-A tail does not function to transport RNA out of the nucleus.  The poly-A tail functions to help ribosome binding.  Expt-  Remove the Poly-A tail from some RNA and see whether it is transported out of the nucleus or not.