Final answer:
Protein Kinase C (PKC) has different roles in growth factor signaling compared to immune responses. During growth factor signaling, it triggers growth and other cellular responses through a phosphorylation cascade; in contrast, during immune responses, it modulates inhibitory proteins impacting transcription related to immunity.
Step-by-step explanation:
The signaling role of Protein Kinase C (PKC) varies depending on the type of external stimulus it responds to. During growth factor signaling, PKC is activated by the generation of diacyl glycerol (DAG) and inositol triphosphate (IP3) produced by the enzyme phospholipase C, after an effector molecule binds to its receptor. This binding causes calcium ions (Ca2+) to be released and along with DAG activates PKC, which then initiates a phosphorylation cascade resulting in cell growth and other specific cellular responses.In contrast, during an immune response, PKC plays a role in modulating the activity of inhibitory proteins like IK-B. PKC phosphorylates IK-B, which leads to the disassociation from NF-KB (a transcription factor), thereby allowing NF-KB to enter the nucleus and promote gene transcription related to the immune response.
Thus, in response to the original question, PKC activates different downstream pathways during growth factor signaling and during immune responses, which distinguishes its signaling roles in these distinct scenarios. Therefore, the correct answer to the student's question would be 'a. PKC activates different downstream pathways'.PKC's signaling role changes in response to growth factor signaling versus an immune response. During growth factor signaling, PKC is activated and exhibits kinase activity, leading to the phosphorylation of downstream signaling molecules and the initiation of a phosphorylation amplification cascade. On the other hand, during an immune response, PKC is inactivated as it interacts with signaling inhibitors and turns off the immune cascades.