Cell signalling Flashcards
What are the principles of cell signalling?
Conversion of a message from one form into another - signal transduction.
Target cells have receptors for signalling molecules.
Most cells both generate and receive signals.
What are the ranges of different signals?
Endocrine - hormones, over long distances.
Paracrine - cells signal to near neighbours.
Neuronal
Contact-dependent - signals to direct neighbours, cell to cell contact.
How does direct cell-cell contact regulate cell differentiation?
One unspecialised epithelial cell develops into a nerve cell.
Has to tell the other cells not to develop.
Signal propagated by pair of ligand receptors - Delta and Notch - signals to neighbour not to specialise.
Found in blood vessel formation and nerve cells.
How does the same signal induce varying responses?
Depends on receptor and intracellular machinery.
Acetylcholine can act on muscle cells - affects contractility.
Salivary cells - increase production of saliva.
Skeletal muscle cell - contraction.
Cells only respond if they have appropriate receptors.
How does cell behaviour depend on multiple extracellular signals?
Cells are integrating a variety of signals.
Cells have many receptor types.
Cells respond to multiple signals simultaneously.
Different signals must be integrated by the cell.
Different combinations of signals result in different behaviour.
How can cell responses be fast or slow?
Change in contraction of heart takes milliseconds, requires all the proteins being there, and functioning differently by post-translational modification.
Cell proliferation requires new proteins to be made, takes minutes to hours.
How do signals enter the cells?
Signal comes to outside of cell, depending on its chemical nature it may or may not go through the plasma membrane.
Small, hydrophobic molecules can diffuse through - steroid hormones, cortisol.
Large, hydrophilic cannot diffuse so require receptor on cell surface.
How does cortisol enter the cell?
Cortisol can diffuse across the membrane, then binds to its nuclear receptor protein.
The activated receptor-cortisol complex moves into
nucleus, then binds to regulatory region of target gene and activates transcription.
How does Nitric Oxide enter cells?
Small, hydrophobic molecule that can diffuse across plasma membranes.
It triggers smooth muscle relaxation in blood vessel walls.
How do hydrophilic molecules enter the cell?
Primary transduction, transmission of signal from outside to inside.
Intracellular signalling molecules make changes to various effector proteins which affect cell response - metabolism, movement - cytoskeleton and gene expression.
What are the features of signalling pathways?
Primary transduction takes the signal from the outside to the inside.
Relay - spreads the signal through the cell.
Amplification - makes the signal stronger, so that a few extracellular signal molecules can result in a large intracellular response.
Integrate - Receiving more than one signalling input and
generating appropriate output.
Distribute - pass on the signal to more than one pathway.
What are protein kinases?
Phosphorylates their substrates on serine, threonine or tyrosine residues - has OH group.
ATP is used to add phosphate to add to OH. This has 2 negative charges and causes a conformational change and therefore its activity.
Can create a docking site.
What are protein phosphatases?
Phosphatases remove phosphate to switch it off.
Protein phosphorylation can:
Alter conformation and activity
Enable recruitment of effector proteins - creates a docking state.
How does protein phosphorylation alter the activity of proteins?
Can activate proteins or deactivate them.
How can protein kinases transduce signals?
Signal in to the protein causes phosphorylation.
Increases activity, protein can give out a signal, usually by modifying another protein.
