Term
| what are the 3 stages of cell signalling? |
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Definition
reception
transduction
response |
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Term
| which stage involves the detection of a signal molecule? |
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Definition
reception
this involves detection by cell of a signal molecule usually originating from the outside of the cell |
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Term
| what must a signalling molecule directly interact with in order for a signal to be detected? |
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Definition
a receptor on the cell surface or inside the cell
this stage is referred to as receptor binding |
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Term
| what are signalling molecules also known as? |
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Definition
| Ligands - small molecules that can lead to the change in the shape of a protein or aggregation of 2 or more receptors to interact with other molecules |
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Term
true or false?
the reception of a signal depends on the receiver? |
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Definition
| true. analogy; a radio station broadcasts at a certain wavelength but you only hear it if you are tuned into the same wavelength. |
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Term
| what messengers are detected by membrane bound receptors, are water soluble and often too large to pass through the membrane? |
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Definition
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Term
| which messengers can move through the lipid layer of the pm thus can be located inside the cell? |
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Definition
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Term
| name the 3 main types of receptors in the plasma membrane |
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Definition
G protein coupled receptors
receptor tyrosine kinases
ion channel receptors
most water-soluble signal molecules bind to specific sites on receptor proteins that span the pm. |
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Term
| animals do not have receptor tyrosine kinases. what do they have instead? |
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Definition
| RLK receptor like kinases |
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Term
| name the largest family of cell surface receptors |
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Definition
| G protein coupled receptors (GPCR) ~ 1000 encoded in human genome. |
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Term
| A GPCR is a pm receptor that spans the membrane in which form? |
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Definition
7 even alpha helices.
GPCR work with the help of a G protein |
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Term
| what does moving around phosphate in a cell do? |
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Definition
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Term
| a G protein can bind GTP and GDP. what do these acronyms stand for? |
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Definition
GTP guanosine triphosphate
GDP guanosine diphosphate
G protein is a molecular switch, it can switch on or off. |
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Term
| when GDP is bound to the G protein the G protein is ... |
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Definition
inactive.
ie. the switch is OFF |
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Term
| when GTP is bound to the G protein, the G protein is.. |
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Definition
activated.
ie, the switch is ON |
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Term
| G Proteins are made from 3 subunits. What are they? |
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Definition
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Term
| which side of the cell membrane are G proteins loosely attatched to? |
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Definition
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Term
when a signalling molecule binds to the extracellular side of a GPCR the receptor becomes activated.
what happens in this activation stage? |
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Definition
there is a change in the shape of the receptor - the cytoplasmic side of the GPCR binds to the inactive G protein.
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Term
| the interaction between G protein and GPCR leads to GTP displacing GDP which activates the G protein. what do activated G proteins do? |
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Definition
| they dissociate from GPCR and diffuse along the membrane binding to an enzyme which cause change of shape in enzyme leading to activation leading to a cellular response. |
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Term
| what determines how often signalling occurs? |
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Definition
ligand concentration.
binding of ligands is reversible and ligands bind and dissociate many times |
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Term
| the changes in enzyme and G protein are temporary because the G protein also functions as a GTPase enzyme - what does this enzyme do? |
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Definition
| it hydrolyzes GTP back to GDP. this inactivates the G protein and it leaves the enzyme making it available for reuse. |
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Term
t or f
epinephrine or adrenaline from adrenal gland stimulates glycogen breakdown in liver and skeletal muscle during stress - this is an example of a signalling pathway that uses G protein coupled receptors |
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Definition
true
60% of all medicines used exert their effects by influencing G protein pathway |
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Term
| what do whooping cough (pertussis), cholera and botulism have in common? |
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Definition
| the bacterial toxins in them interfere with normal G protein coupled receptor function |
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Term
| receptor tyrosine kinases (RTK) are also membrane bound receptors but how do they differ from GPCR? |
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Definition
| they have intrinsic enzyme activity. |
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Term
| how do RTK act as tyrosine kinases? |
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Definition
they add phosphate residues onto other proteins.
A RTK can trigger multiple signal pathways at once
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Term
| what is abnormal functioning of RTK associated with? |
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Definition
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Term
| before ligand binding the receptors exist as inactive monomers. what 3 things are found on each monomer? |
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Definition
extra cellular ligand binding site
membrane spanning region
intracellular tail containing multiple tyrosines |
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Term
| binding of ligand eg. growth factor causes the 2 monomers to come together. what is the structure when they come together known as? |
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Definition
a dimer.
dimerisation activates the tyrosine kinase region of EACH monomer. each tyrosine kinase adds a phosphate from an ATP molecule to a tyrosine on the tail of the other monomer (6 in total) . the receptor is now fully activated and recognised by specific relay proteins inside the cell. |
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Term
| what specific tyrosine must relay proteins bind to in order to be activated? |
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Definition
phosphorylated (fully activated tyrosine)
now each activated protein triggers a transduction pathway |
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Term
| abnormal RTK linked to cancer. name the one RTK associated with some breast cancer patients and what treatment is approved for early stage breast cancer? |
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Definition
excessive levels of HER2 - human epidermal growth factor 2
poor prognosis
herceptin, a monoclonal antibody that binds to receptor is approved for early stage breast cancer. it binds to HER2 on cells inhibiting their growth and division |
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Term
| name the channels that are important in the nervous system eg. neurotransmitter molecules released at a synapse between 2 nerve cell |
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Definition
Ligand-gated ion channel.
some gated channels are control by electrical impulses. these are known as voltage-gated ion channels and are crucial to the functioning of the nervous system |
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Term
| many drugs exert their effects through modulating ion channels. what does Verapamil do? |
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Definition
| it is a calcium channel blocker used to treat hypertension and other cardiovascular disorders |
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Term
| many drugs exert their effects through modulating ion channels. what does Lamictal do? |
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Definition
| it is a sodium channel blocker used for treatment of epilepsy |
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Term
| many drugs exert their effects through modulating ion channels. what does Lidocaine do? |
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Definition
| it is a sodium channel blocker and is used as a local anaesthetic |
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Term
| many drugs exert their effects through modulating ion channels. what does Glipizide do? |
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Definition
| it is a potassium channel blocker used in the treatment of diabetes |
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Term
| what does a chemical messenger need to be in order to cross the membrane and activate receptors? |
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Definition
small or hydrophobic.
eg steroid thyroid hormones and nitric oxide, of animals.
plant steroids called Brassiunosteroids |
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Term
t or f?
activated hormone-receptor complexes can act as a transcription factor to turn on specific genes? |
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Definition
true.
eg. testosterone secreted by cells in testes > travels in blood and enter cells in body > only cells with appropiate receptors can respond >testosterone activates and intercellular receptor > hormone receptor complex enters the nucleus and acts as a transcription factor > mRNA produced > protein synthesis
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