Cell Signalling Flashcards
What cell signalling mediates;
Reaction to signals from environment
Communication between cells
Teamwork of cells in multicellular organism
Signalling pathway includes
Signal cells
Signal molecules
Receptors
Target cells
Signal cells
Produce specific type of signal molecules
Signal molecules
Hydrophilic (large, do not diffuse through membrane)
Hydrophobic (small, diffuse through membrane)
Receptors
Located on target cell
Can distinguish signal molecule & specifically react to it
Target cells
Transfers the extracellular signal to intracellular & thus control the cell behavior
Stages of cell signalling
Reception
Transduction
Response
Reception
Cell detects a signalling molecule from outside the cell
Chemical message binds to protein on cell surface
Transduction
Signalling molecule binds to receptor & alter its protein
Signal usually starts cascade of reactions
Response
Signal triggers a specific cellular response
Responses can vary from turning on a gene, activating an enzyme, rearranging the cytoskeleton
Types of extracellular signals
Physical signals
Chemical signals
Physical signals
Light, heat, gravitation, pressure, magnetic field
Chemical signals
Hormones
Neurotransmitters
Neurohormones
Cytokins
Cytokins
Proteins produced by cell as a signals for proliferation, differentiation or survival of cells
Forms of extracellular signalling
Endocrine Autocrine Paracrine Contact-dependent Neuronal
Types of receptors
1) Receptors connected with ion channels
2) Receptors with G-proteins
3) Receptors connected with enzymes
Diacylglycerol
Remains in the membranes, 2 signalling roles
1) activate PKC
2) Can be cleaved to release arachidonic acid
Tyrosine-kinase receptors
Part of receptor on cytoplasmic side serves as an enzyme which catalyzes the transfer of P groups from ATP to the AMM tyrosine on a substrate protein
Phosphorylation
Activation of proteins
ATP is used a sa donor of P group
Paracrine Signalling
Cells communicate over relatively short distances
Allow cells to locally coordinate activities with their neighbors
Paracrine Signalling example
Especially during development
“Tell” their neighboring group of cells what identity to take on
Autocrine Signalling
Cell signals to itself, release a ligand that binds to receptors on its own surface
Autocrine Signalling example
Development - help cells take on & reinforce their correct identities
Endocrine Signalling
When cell need to transmit signals over long distances
Signals (hormones) are produced in one part of the body & travel through the circulation to reach far-away targets
Endocrine Signalling example
Pituitary release GH (growth hormone) = promotes growth
Thyroid release tyrosine = increase metabolism
Endocrine glands that release hormones
Thyroid
Hypothalamus
Pituitary
Contact-dependent
Gap junction - tiny channel that directly contact neighboring cells
Allow small signalling molecules to diffuse between cells
Contact-dependent outsome
Transfer of signalling molecules transmits the current state of 1 cell to its neighbor
Allows group of cells to coordinate their response to a signal that only 1 of them may have received
Neuronal Signalling
Nerve cells transmits signals
Neuronal Signalling Steps
Neuron fires -> electrical impulse move through cell & down its axon
Reach synapse & triggers release of neurotransmitters that cross gap between cells
Bind to receptors at receiving cell & cause a chemical change inside cell
-> Neurotransmitters are quickly degraded/taken back up by sending cels -> resets system so ready for next signal
Receptors connected with ion channels
Ion channels that can open in response to binding of a ligand
Receptors connected with ion channels
Ions cross membrane through special channel by binding to protein structures on extracellular region that changes their conformation
Changes in ion levels inside cell can change activity of other molecules to produce a response
Receptors connected with G protein
Large family of cell surface receptors that share common structure + method of signalling
