Question

A kinase could act as a signal integrating device if it:

Initiates a phosphorylation cascade

The kinase is regulated by two enzymes activated by distinct signals

Phosphorylates more than one substrate in response to a signal

Can autophosphorylate

Becomes constitutively active

Answer 1

A kinase could act as a signal integrating device if it:

1. Initiates a phosphorylation cascade: The major function of a kinase is to phosphorylate its substrate. Phosphorylation can activate and inactivate a protein. So to initiate a signaling cascade a kinase must phosphorylate its substrate. So this is correct

2. The kinase is regulated by two enzymes activated by distinct signals: Distinct ligand binding is required to activate the signaling cascade via the kinase. Regulation by two different enzymes (A separate Kinase and a phosphatase) is required to activate and inactive it. So this is correct.

3. Phosphorylates more than one substrate in response to a signal: In response to a signal (ligand binding), a kinase will phosphorylate a distinct substrate of the signaling pathway. So this is incorrect.

4. Can autophosphorylate: Receptor Tyrosine kinases are known to autophosphorylate themselves after ligand binding and dimerisation. So this is correct.

5. Becomes constitutively active: If a signaling kinase is becomes constitutively active then the pathway will be active irrespective of the presence of a ligand. So, this is incorrect.

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