8 - Principles of Signalling - Williamson Flashcards
give the equations for Kd, proportion of receptors bound in a cell and the eqn that allows us to plot the Michaelis - Menten eqn
Kd = k off/ k on = [LR] / [L] [R]
proportion of R bound = [LR] / [R] + [LR]
[L] / [L] + Kd
what does Kd highlight?
the point at which the R is most sensitive to any change in [L]
- when we have lower [L] R -> OFF
- higher [L] R -> ON
- here, [L] makes most difference to whether R bound or not therefore makes most difference to signalling pathway
why is this mid range Kd important
- if R has too high affinity, then background L levels will bind R
- if too low, too high [L] needed to activate R
what are the 7 conclusions that can be drawn with regards to R binding and subsequent signalling?
1) Kd should be around physiological L conc
2) strong affinity means that dissociation is too slow. cell needs an active method of stopping signal
3) avidity = good alternative. weaker binding but faster dissociation
4) most signals require amplification
5) to avoid random activation from signalling noise, cell requires many of its Rs to be activated and therefore a lot of individual signals
6) cells will continuously turn off these random signals to ensure genuine signals get through - action of phosphatase
7) on/off signalling behaviour requires cooperatively eg action of multiple components interacting
give an example of when extracellular conc is around the point of Kd
eg hGH receptor Kd = 10^-10
extracellular hGH conc ranges from 10^-11 to 10^-9 M
state why a strong Kd is good?
generally high affinity means that the body doesnt have to produce too much because only low L conc required for signal
what happens if Koff is too high? what mechanisms are put in place to reduce Koff?
when Koff too high, the half life of the L is also too high.
if the cell was only to rely on natural degradation of S to stop signal wouldn’t work
therefore…
- eg GPCRs have Rs recycled during internalisation -> endosomes. acidification of endosome -> removal of L from R and R goes back to surface.
- eg GPCRs once bind R, become P. can now bind arrestins to stop signal. however R still bound by L
- acetylcholinesterase present at high conc in synapse. breakdown ACh therefore allowing next nerve impulse
to arrive
name some inhibitors of acetylcholinesterase
toxins and nerve poisons eg sarin
name some other hormones taken up by transporters, give some disorders that these inhibitors are used to treat and name some of these inhibitors
serotonin, dopamine
inhibitors for uptake of these molecules used to treat obesity, ADHD eg prozac specific inhibitor of serotonin uptake. cocaine = best known inhibitor
draw a diagram showing how a high avidity comes about
343 - 8 word
give an example of a signalling pathway and amplification
one photon leads to breakdown of around 10^5 cGMP being broken down through activation of phosphodiesterase
is it good for a cell to have 1R that can either be turned off or on
NO, random events such as protein changing its structure (because theyre floppy) can result in signal turning ON. want to have multiple Rs being activated to turn on signal
give an example of when a threshold level of signal is reached
eg TGFB R activation leads to SMAD P and entering into nucleus however lots of TGFB Rs need to be activated to give rise to any significant change within cell
how can the cell avoid random signals that can be created?
action of nonspecific phosphatases to remove these random signals
this is at a rate higher than background phosphorylation
until a genuine signal arrives so phosphorylation swamps phosphatase activity
why is it good to have cooperativity of Rs, give an example of this
allows for Rs to become much more switch like
eg having multiple MAP kinases in the kinase cascade allows much more switch like behaviour
all 3 kinases need to be switched on to get signal
