Cell Communication SEM1 Flashcards
What are gap junctions
Cell-cell junctions between apposed plasma membranes - direct connect for small soluble signals (not large molecules)
What signals are moved across membranes through vesicle fusion (exocytosis)
-proteins
-peptides
-amino acids
-nucleotides
What signals are released through channels and transporters
Ions
What does it mean for a signal to be released constitutively
Passive flow down concentration gradient
What does it mean for a signal to be evoked when released
Channels can be gated
What signals are released through free diffusion
Steroids
Gasses
(Both are hydrophobic)
What are the three main forms of signaling of secreted molecules
-paracrine
-synaptic
-endocrine
What is the action of signals released through paracrine signaling
Released signals only affect cells in the immediate cellular environment
How do signals terminate in paracrine signalling
-uptake into neighboring cells
-destruction by extracellualr enzymes
-sequestration by extracellular matrix
What is the action of signals released through autocrine signalling
The signal is released onto the same cell type
What can a group of identical cells in autocrine signaling result in
Group of identical cells produces a higher concentration secreted signal than a single cell can - 1 cell releases signal, binds to receptors on neighboring cells => amplify signal
What does the activation of the dendrite trigger in synaptic signaling
-activation at dendrite triggers electrical impulses (action potentials) along neuronal axon
What happens when an impulse reaches the nerve terminal in synaptic signalling
It stimulates secretion of chemical neurotransmitters
What is the role of endocrine cells
Secrete signals - hormones - into the blood
How is specificity of signalling maintained in endocrine signalling
Only certain cells have appropriate receptors to recognise specific hormone
How can specificity of signalling be achieved by synaptic signalling
Arises from the physical location of the signalling site and the receptor
How can specificity of signalling be achieved by endocrine signalling
Arises from combination of different signalling molecules being recognised by equally array of receptors (wide range of signals and receptors)
What is the difference in distance travelled by endocrine and synaptic signalling
-endocrine targets anywhere in body - long distance
-synaptic targets 100nm away from signal -short distance
What is the difference in speed between endocrine and synaptic receptors
-endocrine realised on diffusion and blood flow to reach target - slow
-synaptic signals take <1 sec to reach target - fast
What is the difference between the affinity of target between endocrine and synaptic signalling
—endocrine signals diluted in bloodstream - receptors high affinity
-synaptic signals highly concentrated at synapse - receptors low affinity
Which cells do not require receptors
Cells that use signalling via gap junctions or gasses
What does binding of the signal (ligand) cause
Receptor activation
What does receptor activation stimulate production of
Stimulates production of intracellular signals
Where are receptors located in relation to steroid signalling
Receptors located within the cell
What are the 4 major types of receptors
-ionotropic
-metabotropic
-kinase
-steroid
Function of ionotropic receptors
Allow flow of ions across membranes
Function of metabotropic receptors
Generate new signals inside cell (2nd messengers)
Function of kinase receptors
Modify existing molecules to generate new signals
Function of steroid receptors
Change expression of genes
What effect can ionotropic receptors induce
Changing the membrane potential
What are the two types of ionotropic receptors
Excitatory - influx of positive charged ions e.g Na+ or Ca2+
Inhibitory - influx of negative charged ions e.g Cl-
How do metabotropic or G-protein-linked receptors act to regulate the activity of a plasma-membrane-bound target protein
The receptors act indirectly to a target which is either an enzyme or an ion channel
What is the intermediate between the receptor and target in metabotropic processes
A trimeric G-protein
What are the 3 subunits of G-proteins
Alpha (a), beta (B) and gamma (y) subunits
What do the subunits of g-proteins bind to
Bind to metabotropic receptors which have 7 transmembrane domain structures (Metabotropic and G protein linked receptors have same structures)
How is the G-protein attached to the receptor and membrane
Attached to receptor by its alpha (a)- subunit
Attached to membrane by its alpha(a) and gamma(y)-subunits
What does the ligand binding cause the alpha(a subunit to release
Releases GDP for GTP (gtp replaces gdp and binds to alpha subunit of protein)
What does ligand biding and the a-subunit release of GDP and GTP cause
1)activation of the alpha(a) subunit and
2)release of the beta(B)/gamma(y) subunits
What does the activation of the alpha-subunit allow for
To alter enzyme activities therefor change concentration of intracellular signals inside cell
How is signalling from metabotropic receptors terminated
Terminated by hydrolysis of GTP to GDP by the alpha-subunit
What are kinase receptors
Either enzymes themselves or associated with enzymes
What is the structure of a kinase receptor
One transmembrane domain with a ligand binding site outside the cell and enzyme activity inside cell
