lecture 13: cell signalling Flashcards
what is transduction?
converting a message into another form
communication is via what for cells?
chemicals (hormones, neurotransmitters)
what are the 3 steps to signal transduction overview?
1) receptor
2) transduction
3) response (cytoplasmic or nuclear)
what does a signalling molecule do?
binds to a receptor protein, causing it to change shape
what are the 4 main types of receptor proteins?
-GPCRs
-RTKs
-ion channel receptor
-intracellular receptors
what happens during step 1 of cell signalling, reception?
a signalling molecule binds to a receptor protein causing it to change shape
what is a GPCR?
-largest family of cell-surface receptors
-GPCR is an integral plasma membrane protein that works with the help of a G-protein
-they are G-protein coupled receptors
what is the role of the G-protein in GPCRs?
G-protein acts as an on/off switch:
-if GDP is bound to the G-protein= inactive
-if GTP is bound to the G-protein= active
what are the two molecules that turn the G-protein on /off?
GTP (ON)
GDP (OFF)
what is a ligand?
signalling molecule!
What are the steps in GPCR reception?
what are RTKs?
-Receptor tyrosine kinases
-RTKs are membrane receptors that attach phosphates to tyrosine amino acids
-RTKs can trigger multiple signal transduction pathways at the same time
true or false, RTKs can only trigger one signal transduction at a time.
false! can trigger multiple!
what is a kinase?
enzyme that phosphorylates other proteins/molecules
what are examples of RTKs?
-insulin receptor
-growth hormone receptor
what are the steps in RTK reception?
what are ion channel receptors?
1) when no signalling molecule is bound, ion channel is closed
2) signalling molecule binds to the ion channel causing the channel to open
3) when signalling molecule concentrations drop and comes off the ion channel, the channel closes
the ions that enter lead to a cellular response!
what are intracellular receptors?
-intracellular receptor proteins are located in the cytosol of nucleus of target cells
-ligands are small or hydrophobic molecules that can readily cross the plasma membrane
-activated hormone-receptor complex can act as a transcription factor to activate transcription of specific genes
what are examples of molecules that can have an intracellular receptor.
has to be a small or hydrophobic molecule that can cross plasma membrane, like steroid and thyroid hormones
wold a peptide/protein hormone also have an intracellular receptor?
no, cause proteins cant just pass by the cell membrane, since they’re too big
what are the steps to intracellular receptors?
what is transduction?
cascades of molecular interactions (mostly between proteins) that relay signals from receptors to target molecules in the cell
true or false, transduction often involves multiple steps?
true!
what are the advantages of transduction involving multiple steps?
-provides more opportunities for coordination and regulation of the cellular response
-amplification of signal
what are the 2 types of transduction pathways?
protein phosphorylation and second messenger
what is protein phosphorylation?
signal is transmitted by a cascade of protein phosphorylations
what do protein kinases do? what is this process called?
transfer phosphates from ATP to proteins (phosphorylation)
what is the link between phosphorylation and a protein being activated or not?
active= phosphorylated
inactive= unphosphorylated
what are protein phosphatases and what do they do?
they remove phosphates from protein (dephosphorylation)
why is protein phosphorylation a good process for the cell?
turns processes off and on as required by the cell
why are protein kinases helpful in protein phosphorylation?
Proteins being phosphorylated and dephosphorylated in the cascade are often protein kinases; active protein kinase will activate the next kinase in the pathway and so on…
what does protein phosphorylation look like?
what are second messengers?
Second messengers are small, non-protein, water-soluble molecules or ions that spread through the cell by simple diffusion
what pathways do second messengers participate in?
pathways initiated by GPCRs and RTKs
what are common second messengers?
- Cyclic AMP (cAMP)
- Calcium ions
- Inositol triphosphate (IP3)
- Diacylglycerol (DAG)
what is the enzyme that converts ATP into cAMP?
adenylyl cyclase
what does phosphodiesterase do?
enzyme in the plasma membrane, converts cAMP to AMP to terminate the signal
how do G protein-coupled receptors and RTKs trigger cAMP formation?
by activating adenylyl cyclase
why are calcium ions important?
-they can act as a second messenger in many pathways
-important cause cells can easily regulate its concentration
what is the link between inositol triphosphate (IP3) and calcium channels?
some calcium channels can be opened by IP3
how do cells regulate calcium ion concentrations?
-Ca2+ can be actively pumped into the ER from the cytosol
-Ca2+ channels can we opened to allow the flow of Ca2+ into the cytosol
what are the steps to opening an IP3 gated calcium chanel?
1) phospholipase gets activated by an active G-protein
2) active phospholipase cleaves PIP2 to release IP3 and DAG
3) IP3 binds to IP3-gated Ca2+ channels in the ER, which opens channel
4) Ca2+ is released from the ER into the cytosol and activates the next protein in the cascade
what are the 2 different types of cell responses?
-nuclear
-cytoplasmic
what’s a nuclear response?
-many signalling pathways regulate the synthesis of enzymes or other proteins by turning on the transcription gene
-the final activated molecule in a signalling pathway may function as a transcription factor
-leads to transcription of gene by activating transcription factor
what’s a cytoplasmic response?
-signalling pathways regulate the activity of enzymes rather than their synthesis
-does not involve gene expression
is a steroid hormone response nuclear or cytoplasmic?
nuclear
what happens during signal termination?
-pathways cant be turned on at all times
-if ligand concentration falls, fewer receptors will be bound and unbound receptors will revert to an inactive state
what happens to transduction molecules when we terminate the signalby dereasing ligand concentration?
-GTPase activity of G-proteins will hydrolyze GTP to GDP
-phosphodiesterases convert cAMP to AMP
-Protein phosphatases inactivate phosphorylated proteins
