Cell Receptors Flashcards
What are chemical messages or molecules that bind to receptors called?
Ligands.
What are receptors?
(Generally) proteins that bind with ligands to elicit an effect within the cell.
What is a second messenger?
A chemical messenger separate from the ligand or receptor that provokes the intracellular response when a receptors binds to a ligand.
What are the four main types of receptors?
Ligand-gated ion channel receptors.
G-protein coupled receptors.
Enzyme-linked receptors.
Intracellular receptors.
What can ligand-gated ion channel receptors also be known as?
Ionotropic receptors.
What do all ionotropic receptors have incorporated within their quaternary (3-D) strucuture?
A central pore (for things to pass through).
How does the central pore of an ionotropic receptor open up?
When an appropriate ligand attaches to the ligand-binding domain on the external surface of the protein.
What is the name given to the process of the receptor changing shape?
Conformation change.
Do molecules pass up or down their concentration gradient through an ionotropic receptor?
Down.
What are G-protein coupled receptors also known as and why?
7-transmembrane receptors as the channel protein snakes in and out the membrane 7 times.
What are the channel proteins linked to in a G-protein coupled receptor?
An intracellular G-protein complex.
What is a G-protein complex made of?
An alpha subunit, a beta-gamma subunit, and an associated GDP molecule.
What part of the G-protein complex is the most variable?
The G-alpha part of the complex, allowing for alternative signal transduction pathways.
What are the steps involved in G-protein activation?
- Ligand binds, causing the G-protein complex to associate with the receptor, causing the GDP molecule to be phosphorylated to GTP.
- The G-alpha subunit dissociates from the G-beta-gamma subunit.
- The G-alpha and the G-beta-gamma subunit can act as second messengers.
- Once the ligand dissociates from the receptor, internal GTPase on the G-alpha subunit hydrolyses GTP to GDP.
- The G-alpha and G-beta-gamma subunits re-associate and are available to the receptor again.
What do enzyme-linked receptors consist of?
These transmembrane receptors ordinarily only consist of one transmembrane domain, which has the ligand-binding domain on the outside and specialised enzymes (usually tyrosine kinase enzymes) on the inside.
What is needed to activate the intracellular enzyme associated with enzyme-linked receptors?
Clustering of more than one receptor protein is needed.
What happens when the intracellular enzyme associated with enzyme-linked receptors is activated?
The enzymes trigger a signalling cascade within the cell.
What is the overall process involved in enzyme-linked receptor activation?
- Ligand binding results in receptor clustering.
- Receptor clustering activates enzyme activity within the cytoplasmic domain.
- The enzymes phosphorylate the receptor.
- The phosphorylation leads to the binding of signalling proteins to the cytoplasmic domain.
- These signalling proteins recruit other signalling proteins and a signal is generated within the cell.
6, The signal is terminated when a phosphatase dephosphorylates the receptor.
What do intracellular receptors act as?
Transcription factors.
What sort of hormones can act on intracellular receptors and why?
Steroid hormones as they are membrane-permeable thanks to their lipophilicity.
How many classes of intracellular receptors are there?
2
What is the structure of a type I receptor?
A receptor located within the cytosol and is associated with a chaperone molecule called a heat shock protein.
How does a type I receptor work?
Once the hormone binds, the HSP dissociates allowing the hormone-receptor complex to form a homodimer with another identical hormone-receptor complex (two hormone-receptor complexes bind together). The homodimer translocates to the nucleus where it binds to DNA and acts as a transcription factors.
How does a type II receptor differ from a type I receptor?
They are located within the nucleus of the cell (vs the cytoplasm) and are already bound to the DNA.
How does a type II receptor work?
Binding of the hormone ligand to the receptor usually results in direct transcriptional regulation by the activated hormone-receptor complex.
