You identify some precursor products in the Adenine synthesis pathway and grow a
ID: 208779 • Letter: Y
Question
You identify some precursor products in the Adenine synthesis pathway and grow a few of your mutants in the presence of these intermediates to determine what order the genes act. Below are your results.
+precursor A
+precursor B
+precursor C
+precursor D
+precursor E
+Adenine
mut1
+
-
+
+
+
+
mut2
-
-
-
-
-
+
mut3
-
-
+
+
+
+
mut6
-
-
-
-
+
+
a. Given these results, draw the best possible ordered pathway for Adenine synthesis. Use arrows to indicate the each precursor being changed into the next precursor and indicate which mutant is responsible for each step.
b. Did your screen identify all the genes responsible for Adenine synthesis? Explain why or why not.
+precursor A
+precursor B
+precursor C
+precursor D
+precursor E
+Adenine
mut1
+
-
+
+
+
+
mut2
-
-
-
-
-
+
mut3
-
-
+
+
+
+
mut6
-
-
-
-
+
+
Explanation / Answer
a. Adenine biosynthesis pathway:
A ---> B ---> C ---> D ---> E ---> Adenine
Alternative pathway:
A ---> C ---> D ---> E ---> Adenine
i. Mut2 can only grow in the presence of Adenine. So, it must be the final enzyme involved in the biosynthetic pathway. So, it must be involved in the conversion of E to Adenine.
ii. Mut6 can only grow in the presence of either E or Adenine. So, it must be the enzyme that is required for the conversion of D to E.
iii. Mut3 can grow only in the presence of C, D, E, and Ade. So, it must be the enzyme that is required for the conversion of B to C.
iv. Mut3 can grow only in the presence of A, C, D, E, and Ade. So, it must be the enzyme that is required for the conversion of B to C. However, mut1 and mut3 are not allelic each other as both show different precursor requirement.
b. The pathway did not identify all the genes responsible for the biosynthesis of adenine.
For example, genes responsible the conversion of C to D and A to B are not identified.
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