Question

A first messenger molecule activates a receptor that stimulates enzyme a, which synthesizes 100 second messenger molecules. In turn, each second messenger activates only one molecule of enzyme b, which once activated, phosphorylates 100 molecules of enzyme c that each phosphorylate 75 molecules of enzyme d. In the last step, each enzyme d phosphorylates 50 transcription factors. How many transcription factors are phosphorylated in response to the first messenger binding to the receptor? how many transcription factors would be phosphorylated if one copy of the enzyme d gene were inactivated (heterozygous genotype) so that there were only half the number of functional enzyme d molecules in the cell? explain.

Answer 1

A total of 3.75 x 10⁷ transcription factors are phosphorylated in response to the first messenger. The number of transcription factors phosphorylated if one copy of the d enzyme is inactivated is 3.7499 x 10⁷.

What is phosphorylation?

Phosphorylation is a posttranslational modification that suffers proteins during the activation of a singling pathway.

Phosphorylation is capable of activating and/or deactivating specific signaling pathways.

In this case, phosphorylation activates a molecular cascade involving the progressive phosphorylation of different substrates.

In this case,  3.75 x 10⁷ transcription factors are phosphorylated in response to the first messenger (100 x 100 x 75 x 50 = 3.75 x 10⁷), whereas the number of transcription factors phosphorylated if one copy of d enzyme is inactivated is 3.7499 x 10⁷ (3.75 x 10⁷ - 50).

Learn more about phosphorylation here:

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