Summary
Cells detect extracellular ligands with receptors and convert them into responses through signal transduction pathways.
In depth
Signalling has three stages: reception (ligand binds receptor), transduction (relay through proteins, often by phosphorylation and second messengers) and response (change in gene expression or activity). Signals may be endocrine, paracrine, autocrine or contact-dependent.
Cascades amplify the signal: one hormone molecule can lead to thousands of product molecules. Termination is as important as initiation, using phosphatases and phosphodiesterases.
Specificity comes from the receptor: only cells with the matching receptor respond, and the same ligand can have different effects in different cells (adrenaline raises heart rate but relaxes airway muscle). Signals can be hydrophilic and bind surface receptors, or lipophilic such as steroids that cross the membrane and bind intracellular receptors that act as transcription factors.
Signals must be switched off: phosphatases reverse phosphorylation, GTPases hydrolyse GTP and receptors are internalised. Errors in this ending step are frequent in disease.
Example: in quorum sensing, bacteria release autoinducers and switch on genes (such as luminescence in Vibrio fischeri) only when the population is dense.
Frequently asked questions
What is Cell Signalling?
Cells detect extracellular ligands with receptors and convert them into responses through signal transduction pathways.
Which area of biology covers Cell Signalling, and how advanced is it?
Cell Signalling is one of the 52 topics in Cell Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Second Messengers, Receptor Tyrosine Kinases, G Protein-Coupled Receptors.
Can you give an example of Cell Signalling?
Adrenaline binding liver cells triggers glycogen breakdown through cAMP.
What should I learn before Cell Signalling?
Work through the Beginner topics in Cell Biology first, such as Cell Theory, Prokaryotic Cell, Eukaryotic Cell, then return to Cell Signalling. Intermediate topics assume the Beginner vocabulary.
What topics are related to Cell Signalling?
The closest topics to Cell Signalling are Second Messengers, Receptor Tyrosine Kinases, G Protein-Coupled Receptors, Nuclear Pore Complex. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Cell Signalling?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Cell Signalling. To practise the whole of Cell Biology, use the Cell Biology quiz.
How is Cell Signalling different from Second Messengers?
Cell Signalling: Cells detect extracellular ligands with receptors and convert them into responses through signal transduction pathways. Second Messengers: Small intracellular molecules such as cAMP, IP3 and Ca2+ that amplify and spread signals from receptors. Read both side by side and note what each one explains.
How should I study Cell Signalling step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Second Messengers and explain the difference aloud. Finally, take the Cell Biology quiz and come back to this page for any question you miss.