Dr. Reichler╣s Bio 212  MW 9-10am          Print Name:_______________KEY__________

Exam #1   Feb. 16, 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 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.     When designing an experiment using the rules of Strong Inference, what is the goal of the experiment?

To disprove or eliminate one or more hypotheses.

 

 

2.     DNA is double stranded, but only one strand is used to make RNA.  Why can each RNA polymerase read only one strand of DNA at a time?

RNA synthesis only occurs in a 3╣ direction.  Since DNA is anti-parallel, only one of the two strands can be read.

 

 

3.     How can mutations lead to changes in proteins?  Where would the mutation be, and what change in the protein would result?  Also, describe a mutation that would not lead to changes in the protein.  (8pts)

By changing DNA, the resulting RNA and protein sequence can be changed.  Substitutions in an exon could change the codon coding for a different amino acid.  Also, additions or deletions of a number of nucleotides not divisible by 3 would cause a frameshift, changing all of the downstream codons.  A mutation that would NOT change the protein could be: outside of the gene, in introns, at the third base of a redundant codon.

 

 

4.     How can a mutation cause a cell to lose the ability to perceive an environmental stimulus?

If the mutation causes the receptor to be non-functional or non-existant then perception would not occur.

 

 

5.     How can two cells responding to the same signal with the same receptor have different responses?

If the cells have different effectors (relay molecules) that can lead to differentsignal transduction and therefore different responses.

 

 

6.     A cell responds to a signal by changing a membrane bound protein to a secreted protein.  How does the cell do this?

If the signal peptide is removed, the protein will be released to the inside of the ER, and eventually secreted.

 

 

7.     Why would reversing the nucleotide order of a promoter cause the wrong protein to be made?

The RNA polymerase will align itself in the opposite direction and read the other strand in the other direction.

 

 

8.     What would happen to a protein if the recognition of the intron/exon border were off by one nucleotide?

A frameshift mutation.  The reading frame of 3 codons would be wrong.

 

 

9.     Describe a gene that 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, splicesome-all cells need to remove introns, snRNA-involved in splicing

 

 

10.  What would need to be changed about a human gene so that it could be expressed in bacteria?  Why?

Removal of introns.  Bacteria do not have introns and cannot remove them.  With the introns additional, incorrect, amino acids will be translated.

 

 

11.  What two pieces of information are encoded by the AUG codon?

Any two of:  The start of translation, the amino acid Met, the reading frame.

 

 

12.  During translation, what hydrogen bonds are made and broken and what covalent bonds are made and broken?  (8pts)

H-bonds made between mRNA and incoming tRNA, broken as tRNA leaves.  Covalent bonds broken between amino acid and tRNA and made between amino acids.

 

 

13.  How could you test which part of a protein was the signal peptide that directed that protein to the nucleus?  (8pts)

Remove various parts of the protein and see whether it is still transported to nucleus.  OR  add various parts of the protein to some other protein, and see whether the hybrid protein is transported to nucleus.

 

 

14.  In what case would transcription take place but not translation?

When making rRNA or tRNA or snRNA.

 

 

15.  Apply rules 1 and 2 of Strong Inference (the parts prior to actually doing any experiments) to answer the following question:  What causes diabetes?  (8 pts)

Must use Strong Inference and make multiple hypotheses and experiments to eliminate hypotheses.  Ex:  hypo╣s-  Diabetes is caused by eating too much sugar.  Diabetes is caused by eating too little sugar.  Diabetes is caused by mutations in the gene for insulin.  Expt-  Feed two groups of people high and low sugar diets, and then test them for diabetes.

 

 

 

Bonus:  What evidence lead researchers to eliminate bacteria or viruses as the cause of scrapie/mad cow disease/CJD?  (3pts)

Either filtering of infected material to show that the infecting particle was smaller then viruses or bacteria, OR destruction of samples DNA/RNA to show that it was not transmitted by these agents.