Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 11.1 External Signals Are Converted to Responses Within the Cell
Cells communicate through chemical signals, converting external messages into internal cellular responses through a process called signal transduction.
Evolution of Cell Signaling
- Cell signaling evolved in ancient prokaryotes and unicellular eukaryotes
- Bacteria use quorum sensing to coordinate behaviors (e.g., toxin secretion, biofilm formation in S. aureus)
- Yeast cells use mating factors to identify and fuse with opposite-type cells
Signal Transduction Pathway
- Three stages of signaling:
- Reception: Signal binds to a specific receptor
- Transduction: Receptor changes shape, triggering internal pathways
- Response: Cell executes activity like gene expression or enzyme activation
Local and Long-Distance Signaling
- Direct contact: Cell junctions or surface molecule recognition
- Local signaling:
- Paracrine signaling: molecules act on nearby cells
- Synaptic signaling: neurotransmitters across synapses
- Long-distance signaling:
- Endocrine signaling: hormones travel via bloodstream to target cells
- Only cells with correct receptors respond
Sutherland’s Discovery
- Epinephrine requires intact cells to activate enzymes
- Proposed that receptors and internal steps are necessary
- Established the model: reception → transduction → response
In a Nutshell
Cells detect external signals and convert them into specific internal responses using a multi-step signaling pathway. This process is fundamental to both unicellular and multicellular life and ensures proper coordination of cellular activities.