Which statement about protein kinase cascades is true?
A) Signal amplification occurs only at the initial step in the pathway.
B) Information received as a signal at the cell membrane can be communicated to the nucleus.
C) Only the first step allows for the specificity of the process.
D) The proteins involved in these pathways are generally not subject to regulation.
E) These pathways function without second-messenger intermediates.

Question

Quizplus · Accepted Answer

Protein kinase cascades allow for the transmission of signals from the cell membrane to the nucleus. This communication occurs through a series of phosphorylation events that ultimately activate transcription factors, which control gene expression in the nucleus. Because information is transmitted through multiple steps, the signal can be amplified at each step, allowing for a greater response to a given incoming signal.

Answer: C 
 While the initial step in a protein kinase cascade helps to determine which pathway is activated, subsequent steps allow for the specificity of the process. Different proteins may be phosphorylated at different steps, leading to distinct downstream effects.

Answer: E 
 Second messenger molecules, such as cyclic AMP, often play a critical role in protein kinase cascades, by activating or inhibiting particular enzymes.

Which Statement About Protein Kinase Cascades Is True