Cascades of molecular interactions relaying signals form receptors to target molecules in cells.
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Does signal transduction involve multiple steps?
Yes - it is a multistep pathway.
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What are the molecules that relay a signal from receptor to response?
Proteins (mostly)
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What do protein kinases?
Transfer phosphates from ATP to protein, in a process called phosphorlyation
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Where does phosphorylation most commonly occur?
On serine, threonin (or tyrosine) residues
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What does phosphorylation normally lead to?
Protein activation
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What do protein phosphates do?
Remove phosphates from proteins.
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What is the process which protein phosphates remove phosphates from proteins called?
Dephosphorylation
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Phosphorlyation and dephosphorylation therefore act as a...
molecular switch - turning activities on and off or up or down.
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The extracellular signal molecule that binds to the receptor is a pathways...
First messenger
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What is a second messenger?
It is a small, non protein, water soluble molecule or ion that readily spreads throughout a cell by diffusion.
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Second messengers participate in pathways initiated by...
GPCRs and RTKs
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What are two common second messengers?
Cyclic AMP and calcium ions.
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What is cAMP?
Cyclic AMP is a widely used second messenger
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What does Adenylyl cyclase do?
It is an enzyme in the plasma membrane that converts ATP to cAMP in response to an extracellular signal.
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cAMP can be broken down by what to form AMP, which is inactive?
Phosphodiesterase
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What is Cholera initiated by?
Drinking water containing the bacterium vibrio cholerae.
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What do the bacteria do?
They colonise the small intestine (forming a biofilm) and produce an enzyme that acts as a toxin.
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How does Cholera effect G-proteins?
It affects a G-protein involved in regulating salt and water excretion.
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How does Cholera affect G proteins, more detail?
The modified G protein is unable to hydrolyse GTP to GDP and is switched on. = COnstant activation of adenylate cyclase and contiunous production of cAMP. High cAMP levels activate the CFTR = efflux of Cl- ions
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Why is calcium an important second messenger?
Because cells can regular its concentration.
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Under normal conditions is intracellular calcium low or high?
It is very low
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In order to keep cytoplasmic concentrations of calcium low, what happens?
Cytoplasmic protein is actively pumped into the ER and/or mitochondria.
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Pathways leading to the release of calcium invovle:
Inositol triphosphate (IP3) and diacylglycerol (DAG)
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What is CaM?
Calmodulin - a very specific calcium modulated protein that contain 4 Ca2+ binding sites
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What does calcium binding do for CaM?
Calcium binding induces conformational changes allowing CaM to bind to other proteins causing activation or inactivation.
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What are the 4 aspects of fine tuning that need to be considered?
Amplifying the signal, specificity of the response, overall efficiency of response, enhanced by scafforlding proteins, termination of signal.
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What are scaffolding proteins?
They are large relay proteins to which other relay proteins are attached
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How can scaffolding proteins increase signal transduction efficiency?
By grouping together different proteins involved in the same pathway.
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Are inactivation mechanisms an important part of cell signalling?
Yes
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Other cards in this set
Card 2
Front
What is transduction?
Back
Cascades of molecular interactions relaying signals form receptors to target molecules in cells.
Card 3
Front
Does signal transduction involve multiple steps?
Back
Card 4
Front
What are the molecules that relay a signal from receptor to response?
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