• Converts signal into a form that produces cellular response

• Occurs via signal transduction pathways (relay molecules)

Key features:

• Signal amplification

• Multiple responses from one signal

• Regulation checkpoints

• Coordination between cells

Mechanisms:

• Phosphorylation cascades

• Second messengers

Protein Phosphorylation Cascade

• Sequential activation of protein kinases

• Each kinase phosphorylates next protein → activates it

Role of enzymes:

• Kinases → add phosphate → activate proteins

• Phosphatases → remove phosphate → deactivate proteins

Importance:

• Acts as molecular switch (on/off)

• Enables signal amplification