Download Arylsulfatase A Model and Gene Map Worksheet

Arylsulfatase A Model and Gene Map
Part I: Inheritance of Metachromatic Leukodystrophy
Examine the pedigree shown below and answer the following questions:
1. What is the likely inheritance pattern illustrated in the pedigree? Upon what evidence did
you base your conclusion?
These materials were created by MSOE Center for BioMolecular Modeling (http://cbm.msoe.edu).
2. What is the probability that the parents in the third generation would have an affected
child? Show how you arrived at your answer.
3. What is the probability that the parents in the third generation would have THREE affected
children and ONE unaffected child? Show how you arrived at your answer.
Part II: 3D Physical Model of Arylsulfatase A
Examine the 3D model of arylsulfatase A and answer the following questions.
1. List the color schemes that highlight the various amino acid sidechains.
2. Note the orange highlighted cysteines which form disulfide bonds in the 3D model of
arylsulfatase A. How many disulfide bonds are indicated in the model?
3. What might the number of disulfide bonds suggest about the environment in which this
enzyme functions?
4. What residue is found at the location where the backbone is colored red?
Part III: Bioinformatics Gene Map
Examine the bioinformatics strip and answer the following questions.
1. On which chromosome is the arylsulfatase A gene (ARSA) located?
2. What function of the arylsulfatase A enzyme is highlighted on the gene map?
These materials were created by MSOE Center for BioMolecular Modeling (http://cbm.msoe.edu).
3. Where in the cell does the arylsulfatase A enzyme perform its action?
4. How might the number of disulfide bonds help arylsulfatase A perform its function in this
environment?
5. How many introns are found in the ARSA gene?
6. Locate and record the starting position of the nucleotide preceeding each of these introns in
the table below.
7. Identify and record the first and last five nucleotides of each intron in the table below.
Intron
Intron Starting
Postion
First Five Nucleotides
Last Five Nucleotides
8. What pattern do you see in the beginning and end sequences of these introns?
9. How many of the introns split a codon?
10. List the name and residue number of each active site amino acid.
These materials were created by MSOE Center for BioMolecular Modeling (http://cbm.msoe.edu).
11. Are these active site amino acids positioned near each other in the linear sequence of
amino acids in the protein?
12. Where are the active site amino acids (colored in CPK in the model) located relative to each
other in the folded protein? How does this compare to where they are located in the linear
sequence of amino acids?
13. Do any of the twenty-five identified mutations (displayed in green on the model and circled
in blue on the map) on the gene map affect the active site amino acids?
14. What type of mutation occurs at nucleotide 189? What is the new codon? How does this
affect the enzyme?
15. Suggest why the mutations at residue sites other than the indicated active site amino acids
might affect enzymatic function.
16. Focus your attention on cysteine 69 (highlighted at the red colored backbone in the 3D
model and shown as serine). What happens to this amino acid residue?
17. Suggest why is it necessary for cysteine 69 to be converted to formylglycine? (Note: This is
a “gedanken” question!)
18. Suggest another way in which an enzyme might supplement the chemistry available from
the twenty possible amino acid sidechains.
These materials were created by MSOE Center for BioMolecular Modeling (http://cbm.msoe.edu).