Final answer:
False. Protein kinases do not always activate their substrate phosphoproteins.Therefore, it is not correct to say that protein kinases always activate their substrate phosphoproteins.
Step-by-step explanation:
False.
The statement is not true.
While protein kinases have the ability to add phosphate groups to target proteins in a process called phosphorylation, this does not always activate the substrate phosphoproteins.
The effect of phosphorylation can vary depending on the specific protein and context.
Some phosphorylation events may activate proteins, while others may inhibit their function or have no effect at all. Therefore, it is not correct to say that protein kinases always activate their substrate phosphoproteins.