Lecture 7 Flashcards
Introduction to Cell Signalling
What is Cell signalling?
Cell signalling is the process where cells interact with their environment and other cells to regulate behavior like growth, differentiation, metabolism, and development.
What happens if a cell fails to receive or respond to signals?
Signalling defects can lead to diseases such as:
Cancer
Heart disease
Diabetes
Neurological disorders
What are the basic components of cell signalling?
Signal: External stimulus or ligand.
Receptor: Detects and binds the signal.
Amplification: Magnifies the signal inside the cell.
Response: Cellular changes, e.g., enzyme activation or altered gene expression.
What is signal transduction?
Signal transduction is the process of transmitting information from an external signal (ligand) through the receptor to elicit a cellular response.
What are ligands, agonists, and antagonists?
Ligand: A molecule that binds to a receptor.
Agonist: Stimulates a signalling pathway (e.g., serotonin).
Antagonist: Inhibits a signalling pathway (e.g., antihistamines).
What is direct contact signalling?
A ligand on one cell binds to a receptor on an adjacent cell.
Common in tissue development, e.g., eye formation in Drosophila.
What are gap junctions, and how do they work?
Gap junctions connect adjacent cells, allowing ions and small molecules (<1.2 kDa) to pass through.
Used in rapid electrical transmission, e.g., electrical synapses between neurons.
What is autocrine signalling?
A cell releases ligands that act on itself.
Common in developmental decisions and cancer (e.g., auto-stimulation of growth signals).
Example: Eicosanoids regulate platelet aggregation, inflammation, and pain.
What is paracrine signalling?
Hormones travel through the bloodstream to distant target cells.
Example: Insulin regulates blood sugar levels.
Can ligands belong to more than one signalling class?
Yes, some ligands perform multiple roles.
Example: Acetylcholine acts as:
A paracrine signal at neuromuscular junctions.
A hormone in endocrine signalling.
What provides specificity in cell signalling?
Receptor Expression: Only certain cells express specific receptors.
Example: Thyrotropin-releasing hormone (TRH) affects the pituitary, not the liver.
Downstream Molecules: Intracellular signalling components differ across cell types.
Example: Epinephrine affects glycogen metabolism in liver cells, not red blood cells.
What is endocrine signalling?
Hormones travel through the bloodstream to distant target cells.
Example: Insulin regulates blood sugar levels.
What is high affinity in cell signalling?
High receptor-ligand affinity ensures effective signalling at low ligand concentrations (e.g., ~10⁻¹⁰ M).
High affinity is achieved through precise molecular complementarity, like enzyme-substrate interactions.
How does amplification work in signalling?
Amplification occurs through enzyme cascades:
A receptor or associated enzyme activates another enzyme, which activates more downstream molecules.
Results in exponential signal magnification within milliseconds.
What is desensitization in cell signalling?
Prolonged exposure to a signal reduces receptor sensitivity.
Example:
Visual desensitization in bright light.
Adaptation to noxious smells.
What is cross-talk in signalling pathways?
Shared components between pathways allow interaction.
Enables integration of multiple signals to produce unified responses.
What is integration in cell signalling?
Cells process multiple signals and produce a combined response.
Example: Activation of epidermal growth factor receptor (EGFR) integrates signals to alter gene expression via MAPK pathways.
How sensitive is cell signalling?
Extremely sensitive; small ligand concentrations (10⁻¹⁰ M) can activate 50% of target receptors.
Example: Signalling molecules like biotin bind to their receptors even at femtomolar (10⁻¹⁵ M) concentrations.
Why is binding in signalling dynamic?
Binding involves continuous association and dissociation of receptor-ligand complexes.
High affinity increases the time a ligand spends bound to its receptor.
