Question

You are studying the live biosynthetic pathway in bread mold that produces a protein necessary for life. Your research group has identified three genes believed to function in the live pathway and has created mutant lines for each: die-21, die-18, and die-1. You have been growing the mutant strains and a wild-type strain on deficient media that does not contain all four of the compounds involved in the live pathway: A, B, C, and D. To determine the order of the genes in the pathway, you add back the compounds one at a time and obtain the following results:

	Deficient media + Compound
Strain	A	B	C	D
Wild-type	+	+	+	+
Die-21	+	-	+	+
Die-18	-	-	+	-
Die-1	+	-	+	-

Plus signs indicate growth, minus signs indicate no growth

a) What is the order of the compounds in the pathway? (left to right = first compound to end compound)

1. A – B – C – D
2. C – A – D – B
3. B – C – D – A
4. B – D – A – C
5. D – C – B – A
6. C – B – A – D

b) What is the order of the genes/ enzymes in the pathway? (left to right = first gene to end gene)

1. Die-21 – Die-18 – Die-1
2. Die-21 – Die-1 – Die-18
3. Die-18 – Die-1 – Die-21
4. Die-18 – Die-21 – Die-1
5. Die-1 – Die-18 – Die-21
6. Die-1 – Die-21 – Die-18

Answer 1

Answer a) The order of the compounds in the pathway (left to right = first compound to end compound) is option D ( B- D- A-C) because Biosynthetic pathway is blocked by mutation which cancels the enzyme needed for growth.

Answer b) The order of the genes/ enzymes in the pathway (left to right = first gene to end gene) is option C ( Die-18 – Die-1 – die 21) because Biosynthetic pathway is blocked by mutation which cancels the enzyme needed for growth.

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