Feeding experiment and biochemical pathway. a) From a mutagenesis screen, five m
ID: 195353 • Letter: F
Question
Feeding experiment and biochemical pathway.
a) From a mutagenesis screen, five mutants (named c9, c10, c14, c18, c21) were identified and they each were found to mutate a different gene. Feeding experiments were done by growing each mutant on minimal medium supplemented by four different known precursors of cytosine (A-D). The results are summarized in the table (+: growth; -: no growth):
Precursor/product
Mutant
A
B
C
D
Cytosine
c9
-
+
+
-
+
c10
-
-
+
-
+
c14
+
+
+
-
+
c18
+
+
+
+
+
c21
-
-
-
-
+
Show a simple linear biochemical pathway of the four precursors and the end product (cytosine). Indicate which step is blocked by each of the five mutations.
(b). What precursor would accumulate in the following double mutants:
c9, c10:
c10, c21:
Precursor/product
Mutant
A
B
C
D
Cytosine
c9
-
+
+
-
+
c10
-
-
+
-
+
c14
+
+
+
-
+
c18
+
+
+
+
+
c21
-
-
-
-
+
Explanation / Answer
A) c18 c14 c9 c10 c21
__D__B__A__C__cytosine
B) What precursor would accumulate in the following double mutants:
c9, c10: B
c10, c14: D
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