Cell to cell comm Flashcards
What are the 4 types of signals?
Neural
Hormonal
Paracrine
Autocrine
How do cells send and recieve signals?
Cells produce and secrete signal molecules. These molecules can then diffuse through extracellular space, present on cell surface or ECM. Cells then have specific receptors
What is short distance signalling? and give 2 examples of it
Contact dependent - cells in close contact, membrane to membrane
Paracrine - extracellular release of signal that acts only locally on neighbouring cells. There is a local mediator involved
What is long distance signalling, give 2 examples
Synaptic and Endocrine
Synaptic - Neurons, electrical signal along axon which is long distance. Release of neurotransmitter across synapse which is shorter distance.
Endocrine - Release of hormone into bloodstream, acts widely throughout body
What is very short distance and give an example?
Autocrine, cells can stimulate themselves if they have receptor for the ligand.
Cancer cells use autocrine signals to stimulate their own survival and prolif
Groups of identical signalling cells can reinforce signals
Gap junctions
A connexon is composed of how many subunits?
6
Gap junctions allow direct communication between what?
Cytoplasm of adjacent cells by small intracellular signalling molecules
Gap junctions allow neighbouring cells to coordinate what?
Responses to a signal
describe cell surface then intracellular receptors
1) hydro what?
2) cannot cross what?
1) Cell surface receptors are hydrophillic so cannot cross the membrane
2) Intracellular receptors can be hydrophobic or lipophilic so they can cross the membrane and small molecules are transported to the receptor via a carrier protein
Cell signalling, describe the hypothetical pathway using 6 steps
1) Signals
2) primary transduction which is the receptor
3) Scaffold and adaptor proteins
4) Transduce and amplify
5) Integrate or diverging mediators (interaction with other pathways)
6) Target proteins diverge the signal to create multiple effects (gene transcription)
Acetylcholine signal can cause different responses in the different cells, name the 3 cells and responses
1) Heart pacemaker cell and acetylcholine signal will case a decreased rate of firing
2) Salivary gland cell and the signal will cause secretion of the chemicals
3) Skeletal muscle cell and the acetylcholine causes muscle contraction
What are the two different receptors for Acetylcholine and how are they different?
Muscarinic and Nicotinic
Muscarinic is G protein, so the acetylcholine binds to a receptor that is bound to intracellular proteins, known as G proteins, which begin the information cascade within the cell
Nicotinic is an ion channel receptor, the binding of the signal to the receptor causes an ion channel to open.
How do intracellular receptors work, use steroid hormones as an example
Steroid molecule is transported in blood by carrier proteins.This molecule then crosses the membrane and binds to the intracellular receptor that has DNA binding domains which inturn activates or repress rexpression.
look at steroid
okay
What are the 3 major classes of cell surface receptors
Ion channel, G protein, Enzyme
What are the two main mechanisms for enzyme coupled receptors?
1) Signal molecule in form of a dimer attaches to the receptor and the base of this receptor has a catalytic domain which is originally inactive but becomes active after joining of the signal molecule
2) Signal molecule joins to the receptor which activates an associated enzyme
What are the 6 classes of enzyme coupled receptors
1) Receptor tyrosine kinases, have kinase activity and phosphorylate Tyrosine on intracellular signal proteins
2) tyrosine kinase associated receptors - associate with othr intracellular proteins that have kinase activity
3) receptor like tyrosine phosphatases - remove phosphate groups from target proteins
4) receptor serine/threonine kinases - have kinase activity and phosphorylate ser and threonine on target proteins
5) receptor guanylyl cyclases - directly catalyse the production of cGMP in cytoplasm
6) Histidine kinas- associated receptors - directly catalyse th production of cGMP in cytoplasm (yeast, bacteria and plants)
Receptor tyrosine kinases secrete what?
growth factors and hormones
Receptor tyrosine kinases have
a) how many transmembrane domains?
b) type of extracellular domain?
c) how many intracellular domains?
a) single
b) highly variable
c) IC domains which are the tyrosine kinase domains
Extracellular signal proteins mostly act through what?
Receptor tyrosine kinases
RTKs
Cell surface bound extraceullar signal proteins also act through what?
RTKs
Ephrins are the largest class of what?
Membrane bound ligands
What are the receptors for ephrins calls?
Eph receptors
How do RTKs work?
Signal protein binds to the ligand-binding domain on the outside of the cell
This enables the intracellular tyrosine kinase domain to phosphorylate selected tyrosine side chains
The side chains on both the receptor proteins themselves and on intracellular signalling proteins
that subsequently bind to the phosporylated tyrosine on the receptors.
So the intracellular proteins bind to the phospho-tyrosine docking sites.
do ephrins
okay
explain how eph receptor signaling works
1) Ephrins bind to the eph receptors which are clustered.
2) The activation of the receptor means receptor dimerisation which then leadsto trans-PO4 on Y.
3) A kinase binds which then leads to phosporylation of ephexin (GEF) so there is now an active cytoplasmic tyrosine kinase and an active ephexin (Rho GEF)
4) The activated ephexin then activates RhoA which means GDP to GTP.
5) Myosin mediated actin filament contaction and growth cone collapse
There is no gene transcription so the response is very rapid
Receptor tyrosine kinases
1) ligand binding causes the receptors to do what?
2) The answer to 1) causes what to happen to each receptor
1) Causes receptors to dimerize
2) Cross phosphorylation of each receptor
How do other intracellular proteins/signalling proteins bind to the RTKs
The phosphorylation of the RTK generates binding sites for these signalling proteins
Binding proteins have what
dfdffinish off
