Cell Signalling Flashcards
What is cell signalling?
Cell signalling is the process of cellular communication that allows us to function as organisms
Why do cells communicate with one another?
- regulate their development and organisation into tissues
-control their growth and division - coordinate their functions
- cell signalling allows the cells to respond to their environment
3 types of cell message
- Chemical
- Electric
- Mechanical
-Light/heat
Why is the type of message important?
- most drug target one step of the cell signalling
- crucial to assess
- efficacity
- interactions
- specificity (side effects)
4 types of extracellular signalling
- Autocrine
- Endocrine
- Juxtacrine
- Paracrine
What is autocrine signalling?
A cell targets itself
- often involved in signal amplification/ attenuation
- deregulated in most cancer cells
What is Endocrine signalling?
A cell targets a distant cell through the circulation
Best example= regulation of glycemia (blood sugar)
What is Paracrine signalling?
A cell targets a neighbouring cell
Synaptic
8 steps of synaptic transmission
1- neurotransmitters are synthesised and stored in vesicles
2- AP arrives at the presynaptic terminal
3- Voltage gated Ca2+ channels open, allowing influx of Ca2+
4- Ca2+ allows vesicles docking and neurotransmitter release
5- neurotransmitter binds to receptors, causing channels to open or close
6- excitatory ( or inhibitory) post synaptic potential is generated
7- Neurotransmitter is removed by glial uptake
8- Vesicular membrane is retrieved from the plasma membrane
What is juxtacrine signalling?
A cell targets a neighbouring cell via direct contact (ligand/ receptor or GAP junctions)
What are 4 extracellular signalling molecules (1st messengers)
- growth factors
- neurotransmitters
- hormones
- cytokines
How are signalling molecules made?
Synthesised and secreted by signalling cells
Produce a specific response in target cells that have specific receptors for the signalling molecule
4 main classes of receptors
Classified according to molecular structure and signal transduction mechanism
- Ligand gated ion channel
- G-protein coupled receptors (GPCR)
- Kinase linked receptor
- Nuclear receptor
What are ligand gated ion channels
- ionotropic receptors
- binding and channel opening is very fast
- involved in fast synaptic transmission
- ligand- binding site on the extracellular side
Nicotinic acetylcholine receptor
Example of ligand gated ion channel
- Permeable to Na+ & K+
- Na+ moves in, K+ moves out of cell
- causes membrane depolarisation
Present at neuromuscular junction= allows muscle contraction
GPCR
- metabotropic ( second messenger coupled) or seven transmembrane spanning receptors
- largest family (more than 1000)
- coupled to intracellular G protein
Example of GPCR receptor
- Variety of stimuli
Examples - Muscarinic ACh receptor
- Adrenoreceptors
- Angiotensin II receptors
Different G proteins can shape the cellular response
Kinase- linked receptor
- Large and heterogenous group
- One transmembrane domain
- Mostly function as dimers
- Kinase= ligand and dimerization leads to phosphorylation
Nuclear hormone receptors
Intracellular receptors
- Cytosol or nucleus
- Ligand- activated transcription factors
Monomeric structure
- Separate ligand and DNA binding domains
- Regulate gene transcription
Nuclear hormone receptor examples
- Steroid hormones
- Thyroid hormones
4 steps in signal transduction
1- first messenger= ligand
2- Receptor
3- Second messenger
4- responds
Example= adrenaline
Example of signal transduction- Adrenaline
Cell= liver or skeletal muscle glands
First messenger= adrenaline
Receptor= beta- adrenergic receptor
Cell response= breakdown of energy reserves to form glucose
What are second messengers?
- Short lived intracellular signalling molecules
- Quick increase in conc following cell stimulation allows transduction and amplification
- Needs to be transient, removal or degradation terminates the response
- Some second messenger can also be first messenger depending on the hierarchy of events
What are the 4 classes of second messengers?
- cyclic nucleotides
- membrane lipid derivatives
- Ca2+
- Gas
