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biosynthetic pathway

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).

Questions:
(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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Solution Preview

a)
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.

b)
w2w2 means an expression of non-functional enzyme White 2 (since both are ...

Solution Summary

The biosynthetic pathway productions. Nonfunctional enzymes are determined.

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