Receptors Flashcards
what are the 4 main types of receptors?
- steroid
- G coupled receptors
- Ion channels
- enzyme linked
what is a G protein coupled receptor?
- single polypeptides that are folded into globular shape and are embedded in the cells plasma memembrane
- 7 segments that span the width of the membrane
what is an alternative name for G protein coupled receptors?
seven-transmembrane receptors
what are G proteins?
specialised proteins that have the ability to bind to the nucleotides GTP (guanosine triphosphate) and GDP
what does heterotrimeric mean?
3 subunits (alpha, beta and gamma)
when the G protein alpha binds to the subunits GTP of GDP, which is active and which is inactive?
GTP= active and GDP=inactive
G protein- what happens to the GDP (which is attached to the alpha subunit) when there is a signal?
The GTP molecule physically replaces the GDP
G protein-what happens to the subunits when there is a signal?
- dissociate into 2 parts (alpha and gamma + beta together) … GTP bound alpha subunit and a beta gamma dimer
- they remain anchored to the plasma membrane
what makes the GPCR remain active?
the GTP being bound to the alpha subunit
what hydrolyses the GTP back to GDP?
GTPase
-then once again a heterotrimer and an inactive GPCR
what is the second messenger in the GPCR?
cyclic AMP
what is cAMP synthesised from?
ATP by the adenylate cyclase
in the GPCR if there is lots of adenylate cyclase and not much cyclic AMP what happens?
you get a high level of cAMP
what does the cAMP act on?
kinases, which then act on transcription factors and other targets to cause transcription of certain genes
what do kinases catalyse?
phosphorylation. ..
- addition of phosphate groups to specific serine, threonine or tyrosine side chains
- in the GPCR phosphorylatiion of transcription factors at the start of a gene
how do kinases case the release of Ca2+?
Ca2+ is stored in the ER, and then the phosphorylation of certain molecules causes the ligand gated ion chanel to release Ca2+P
where are steroid molecules derived from?
from cholesterol molecules
what are the characters of steroid molecules?
lipid soluble, hydrophobic, so they go straight into the cytoplasm
how do steroids influence gene transcription?
the steroid and receptor move into the nucleus and act as transcription factor that are required for promoting the formation of mRNA
How do steroid receptors work?
the steroid moves through the membrane into the cytoplasm, where it meets the receptor, when the receptor and the steroid join they then move into the nucleus together and affect transcription
how does testosterone regulate its own production?
dec. GnRH, decrease in FSH and LH… the hypothalamus controls the release of GnRH depending on the levels of testosterone
negative feedback
How do ligand gated ion channels work?
They open when a ligand binds and allows ions to flow down a gradient
what are examples or a ligand gated ion channels?
serotonin and GABA receptors
what do phosophotases do?
remove phosphate groups
