cell signals and responses Flashcards
How do cells communicate?
Adaptation, coordination and regulation
Secreted molecules
Membrane bound molecules
Gap junctions
What is secreted signalling?
Endocrine- hormone produced enters circulation
Paracrine- local chemical mediator released for cells in immediate area
Autocrine- on itself
Synaptic- neurotransmitters released at synapses and diffuse to post synaptic target cell
How are signals sent?
Signal->reception->transduction->response
What might signals be?
Growth factors Hormones ECM Chemicals Proteins Sugars Synaptic
What might cell response be?
Growth Differentiation Metabolism Apoptosis Gene transcription Secretion Contract/relax Membrane charge Migration
How might the signal be received?
Internal cell receptor
Cell surface receptor
Cells sense extracellular signal
Translate into an intracellular signal
What are intracellular signals?
Must be hydrophobic
Eg. Steroid hormone
Transported into nucleus for response
What membrane receptors are there?
- G-protein coupled (heptahelical)
- Enzyme linked- receptor tyrosine kinase
- Ion channels
What are characteristics of signal transduction?
Specificity and high affinity
Amplification
Desensitisation when signal is present all the time (resensitise when below threshold)
Integration of multiple signals to produce unified response
What are G-protein coupled receptors?
Cross membrane 7 times
Respond to light, taste, smell, hormones
Integral transmembrane proteins
Receptor occupation promotes interaction w G-protein
Initiates signalling through secondary messengers eg. cAMP, Ca2+
How does the G-protein work?
G protein- alpha, beta, gamma subunits and GDP bound to the alpha (inactive)
When GDP is exchanged w GTP- becomes activated and alpha subunit dissociates to interact w other molecules
To turn off- GDP and alpha subunit reassemble w everything back to original state
What is an example of a G-protein coupled receptor?
Beta adrenergic receptor
Binds epinephrine
Alpha unit dissociates to interact w adenylate cyclase (membrane enzyme) which initiates reactions w secondary messengers (ATP->cyclic AMP etc)
Target for meds eg. Beta blockers and beta2 agonists (blood pressure and asthma)
What is phosphorylation?
Kinases binds phosphate to protein to change its shape and charge- turning it on/off
What is a receptor tyrosine kinase?
Cell surface receptor for growth factors, cytokines and hormones
Intrinsic enzyme activity upon ligand binding-
~dimerises
~autophosphorylates
Conformational change allows signalling molecules to bind and initiate downstream cascades
What are scaffold proteins?
Present in cytoplasm
Bind to things and shield them away from signalling pathways
