The production of the purple pigment anthocyanin in flowers is accomplished via a biosynthetic pathway. A biosynthetic pathway consists of a series of enzymatic reactions resulting in the creation of a final end product via several intermediate metabolites. An example of a biosynthetic pathway is shown below:
Substrate ----(white 1)----- Intermediate A------(white 2)----- Anthocyanin
A mutation in the gene WHITE 1 or WHITE 2 will result in the inability to produce anthocyanin and thus cause the flowers to be white. Suppose that WHITE 1 and WHITE 2 are the enzymes in the biochemical pathway for the synthesis of anthocyanin (W1 = functional enzyme 1; w1 = nonfunctional enzyme 1; W2 = functional enzyme 2; w2 = nonfunctional enzyme 2).
(a) Which molecule (substrate, intermediate A, or anthocyanin) is accumulated in a plant that has the genotype "w1w1"? What will be the color of the flowers?
(b) What molecule is accumulated in a plant that has the genotype "w2w2"? Whatwill be the color of the flowers?
(c) What molecule is accumulated in a plant with the genotype "W1w1;w2w2"? What is the color of the flowers
(d) If a W1W1w2w2 plant were crossed with a plant that is w1w1W2W2, what would be the genotype of the progeny? What will be the color of the flowers?
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w1w1 means the plant carries both recessive genes for a non-functional enzyme, and thus will produce a non-functional enzyme that cannot catalyze the reaction from substrate to intermediate A. Thus, there will be a lot of substrate.
w2w2 means an expression of non-functional enzyme White 2 (since both are ...
The biosynthetic pathway productions. Nonfunctional enzymes are determined.
Biosynthetic Pathways in Mutations
You have isolated four different mutants unable to synthesize compound E required
for growth. You know that compounds A through D are involved in the biosynthetic
pathway that produces compound E, but you do not know the order in which they are
synthesized by a wild-type cell. You supplement the growth of each of the 4 mutants
with each compound and assay its ability to support growth. Using the data below,
construct a biochemical pathway indicating the order of the compounds and the step
where each mutation is acting. Explain how you arrived at the map.
A B C D E
1 − − − − +
2 − + + + +
3 − − + + +
4 − − + − +