11-17-2025, 12:07 PM
Thread 3 — Cell Signalling: How Cells Communicate, Coordinate, and Stay Alive
The Hidden Language of Life — Signals, Receptors & Molecular Conversations
Every second, trillions of your cells are “talking” to each other.
They warn, coordinate, adapt, respond, grow, divide, defend, and make decisions —
all through an invisible molecular communication network called cell signalling.
This thread reveals how cells send messages, receive them, and translate signals into real biological change.
1. Why Cell Signalling Matters
Cell signalling controls:
• growth and healing
• immunity
• metabolism
• hormone responses
• brain function
• development
• homeostasis
When signalling fails → cancer, diabetes, autoimmune disorders, neurological diseases.
Cell signalling is the operating system of life.
2. The Basic Parts of a Cell Signal
A signalling event always has three components:
1. Signal molecule (ligand)
Hormones, neurotransmitters, peptides, ions.
2. Receptor
Detects the signal (usually a protein on the cell surface).
3. Response
Change in gene expression, metabolism, movement, division, etc.
Signal → Receptor → Response.
3. Types of Cell Signals
• Autocrine — cell signals itself
• Paracrine — signals nearby cells
• Endocrine — hormones travel through blood
• Synaptic — neurons signal across synapses
• Juxtacrine — physical contact required
Each type allows different ranges and speeds of communication.
4. Major Receptor Types (The Big Three)
A. G-Protein Coupled Receptors (GPCRs)
• largest receptor family
• respond to hormones, neurotransmitters, smells, tastes
• activate G-proteins → huge amplification
• 40% of modern medicine targets GPCRs
B. Receptor Tyrosine Kinases (RTKs)
• control growth & division
• activated by growth factors
• malfunction → cancer
• classic example: insulin receptor
C. Ion Channel Receptors
• open to let charged ions flow
• key to nerve firing & muscle contraction
• extremely fast
5. Signal Transduction Pathways
Once a receptor is activated, the signal is relayed through a cascade.
Common pathways:
• MAPK pathway — growth & differentiation
• PI3K-AKT — survival & metabolism
• cAMP pathway — rapid responses
• Calcium signalling — universal messenger
• JAK-STAT pathway — immune regulation
These cascades amplify signals millions of times.
6. Second Messengers — The Internal Whisper Network
Small molecules that carry the message inside cells:
• cAMP
• cGMP
• Ca²⁺ ions
• IP₃
• DAG
They spread signals quickly and coordinate cell-wide responses.
7. Negative Feedback — Preventing Signal Overload
Cells must avoid runaway responses.
They regulate signalling by:
• degrading the ligand
• inactivating receptors
• turning off kinases
• activating phosphatases
• reducing gene expression
Balance is everything.
8. Real-World Examples of Cell Signalling
• Insulin signalling — controls blood glucose
• Adrenaline signalling — fight-or-flight response
• Synaptic signalling — learning & memory
• Immune signalling — T-cell activation
• Developmental signalling — turning an embryo into a body
Cell signalling is the logic system that builds and maintains life.
9. When Signalling Goes Wrong
• cancer = hyperactive growth signalling
• diabetes = broken insulin signalling
• autoimmune disease = misregulated immune signalling
• Alzheimer’s = disrupted synaptic signalling
Understanding signalling is key to modern medicine.
10. Summary
Cell signalling is:
• the communication network
• the control system
• the decision-making engine of living organisms
Cells don’t act alone —
they are part of a vast biological conversation that never stops.
Written by LeeJohnston & Liora — The Lumin Archive Research Division
The Hidden Language of Life — Signals, Receptors & Molecular Conversations
Every second, trillions of your cells are “talking” to each other.
They warn, coordinate, adapt, respond, grow, divide, defend, and make decisions —
all through an invisible molecular communication network called cell signalling.
This thread reveals how cells send messages, receive them, and translate signals into real biological change.
1. Why Cell Signalling Matters
Cell signalling controls:
• growth and healing
• immunity
• metabolism
• hormone responses
• brain function
• development
• homeostasis
When signalling fails → cancer, diabetes, autoimmune disorders, neurological diseases.
Cell signalling is the operating system of life.
2. The Basic Parts of a Cell Signal
A signalling event always has three components:
1. Signal molecule (ligand)
Hormones, neurotransmitters, peptides, ions.
2. Receptor
Detects the signal (usually a protein on the cell surface).
3. Response
Change in gene expression, metabolism, movement, division, etc.
Signal → Receptor → Response.
3. Types of Cell Signals
• Autocrine — cell signals itself
• Paracrine — signals nearby cells
• Endocrine — hormones travel through blood
• Synaptic — neurons signal across synapses
• Juxtacrine — physical contact required
Each type allows different ranges and speeds of communication.
4. Major Receptor Types (The Big Three)
A. G-Protein Coupled Receptors (GPCRs)
• largest receptor family
• respond to hormones, neurotransmitters, smells, tastes
• activate G-proteins → huge amplification
• 40% of modern medicine targets GPCRs
B. Receptor Tyrosine Kinases (RTKs)
• control growth & division
• activated by growth factors
• malfunction → cancer
• classic example: insulin receptor
C. Ion Channel Receptors
• open to let charged ions flow
• key to nerve firing & muscle contraction
• extremely fast
5. Signal Transduction Pathways
Once a receptor is activated, the signal is relayed through a cascade.
Common pathways:
• MAPK pathway — growth & differentiation
• PI3K-AKT — survival & metabolism
• cAMP pathway — rapid responses
• Calcium signalling — universal messenger
• JAK-STAT pathway — immune regulation
These cascades amplify signals millions of times.
6. Second Messengers — The Internal Whisper Network
Small molecules that carry the message inside cells:
• cAMP
• cGMP
• Ca²⁺ ions
• IP₃
• DAG
They spread signals quickly and coordinate cell-wide responses.
7. Negative Feedback — Preventing Signal Overload
Cells must avoid runaway responses.
They regulate signalling by:
• degrading the ligand
• inactivating receptors
• turning off kinases
• activating phosphatases
• reducing gene expression
Balance is everything.
8. Real-World Examples of Cell Signalling
• Insulin signalling — controls blood glucose
• Adrenaline signalling — fight-or-flight response
• Synaptic signalling — learning & memory
• Immune signalling — T-cell activation
• Developmental signalling — turning an embryo into a body
Cell signalling is the logic system that builds and maintains life.
9. When Signalling Goes Wrong
• cancer = hyperactive growth signalling
• diabetes = broken insulin signalling
• autoimmune disease = misregulated immune signalling
• Alzheimer’s = disrupted synaptic signalling
Understanding signalling is key to modern medicine.
10. Summary
Cell signalling is:
• the communication network
• the control system
• the decision-making engine of living organisms
Cells don’t act alone —
they are part of a vast biological conversation that never stops.
Written by LeeJohnston & Liora — The Lumin Archive Research Division