Final answer:
Hormones are extracellular signals that trigger signal transduction without entering the cell, resulting in metabolic enzyme responses through second messengers like cAMP and phosphorylation by kinases.
Step-by-step explanation:
Hormones are extracellular signals that are not transported into the cells but will trigger transduction and intracellular response to influence serial metabolic enzymes. Upon hormone binding, a signal transduction pathway is initiated. This response can involve changes in cellular activities such as protein synthesis, metabolism, or cell growth.
Key components involved in this process include second messengers such as cAMP, Ca²⁻, inositol triphosphate (IP3), and diacylglycerol (DAG), which facilitate the communication of the signal inside the cell. Enzymes like protein kinase A (PKA) and protein kinase C (PKC), and other tyrosine kinases, then modify proteins through phosphorylation, thus generating appropriate metabolic responses or influencing gene expression. Extracellular environmental signaling can also influence gene transcription, leading to the regulation of protein levels within the cell.
Cells respond to extracellular signals in various ways, such as storing energy or responding to immediate energy requirements. Growth factors stimulate cell growth, whereas disruptions in signaling pathways can lead to uncontrolled growth, as seen in cancer. Termination mechanisms like the degradation of signaling molecules are essential to ensure an appropriate response to signals.