Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 11.4 Cellular Response: Cell Signaling Leads to Regulation of Transcription or Cytoplasmic Activities
The final stage of cell signaling is the cellular response, which may involve changes in gene expression or direct effects on cytoplasmic activities like enzyme function or ion transport.
Types of Responses
Responses occur in the nucleus or cytoplasm
Nuclear responses regulate gene expression (e.g., activating transcription factors)
Cytoplasmic responses alter existing protein activity (e.g., enzyme activation, ion channel opening)
Example: Epinephrine activates a cascade leading to glycogen breakdown in liver cells
Signal Amplification
Enzyme cascades amplify signals at each step
One hormone molecule can trigger production of millions of product molecules
Example: Epinephrine activates a chain reaction that leads to the release of ~100 million glucose molecules from glycogen
Specificity of Responses
Different cells respond differently to the same signal
A cell’s response depends on its unique set of proteins (receptors, relay molecules, enzymes)
Example: Epinephrine increases heart rate in cardiac cells but triggers glucose release in liver cells
Some pathways branch or converge, allowing more complex regulation and cross-talk between signals
Scaffolding Proteins
Large relay proteins that organize other signaling molecules
Hold proteins close together to increase speed and accuracy of signal transmission
Important in neurons and immune cells
Loss of key scaffolding proteins can lead to diseases (e.g., Wiskott-Aldrich syndrome)
Termination of Signals
Signals must be reversible for cells to remain responsive
Signal ends when ligand detaches and relay molecules return to inactive states
Key mechanisms:
GTP hydrolysis in G proteins
Phosphodiesterase degrades cAMP
Phosphatases deactivate kinases
Proper termination resets the system for future signaling
In a Nutshell
Cellular responses include gene regulation and changes in protein activity. Signal pathways amplify the message and are tightly regulated through cell-specific proteins, scaffolding complexes, and reversible mechanisms to ensure precise and efficient communication.