Lecture 14 Flashcards
What is signal transduction?
When an activated receptor starts a chain of events where messages are passed on through the cell to create a cellular response
What does signal transduction often provide?
Opportunities for coordination and regulation of the cellular response
What are the two mechanisms for signal transduction?
Second messengers and phosphorylation
What is the second messenger pathway often used by?
The G protein-coupled pathway
What are the second messengers used by GPCRs?
cAMP, cGMP, Calcium ion, inositol 1,4,5-triphosphate, diacylglycerol
What is the GPCR pathway of second messangers?
Intracellular molecules that change in concentration in response to receptor activation, this transmits signals from receptor to molecules as they are not attached to the membrane
What do phosphorylation and dephosphorylation events do?
Turn protein activity on and off as required
What is phosphorylation?
When the protein kinase transfers phosphates from ATP to protein
What is dephosphorylation?
When the protein phosphatase rapidly removes the phosphates from proteins to control signal transduction
What does signal transduction using protein kinase create?
A phosphorylation cascade
What are some mechanisms of signal transduction to regulate cellular activity?
Ligand dissociation, internalisation, phosphatase
What is internalisation?
The receptor is removed from the cell surface through endocytosis so it can no longer respond to a ligand
What is GPCRs?
The use of G proteins to start signal transduction, GPCR activates G protein which further communicates with other proteins in the cell
What are the two types of G protein?
G-alpha-s and G-alpha-I
What is G-alpha-s
Stimulatory G protein, which activates an enzyme called adenylate cyclase
What is the G protein made up of?
1x alpha, beta and gamma subunits
What is G-alpha-I
Inhibitory G protein, which decreases the activity of adenylate cyclase
What is the process of signal transduction for Gs-coupled GPCR?
Agonist ligand binds to GPCR which activates G-alpha-s protein to activate adenylate cyclase to increase the levels of cAMP and simulate the protein kinase A
What is the process of signal transduction for Gs-coupled GPCR with the glucagon receptor?
Receptor activation from glucagon from the liver cells causes G protein activation and further signal transduction events leading to glycogen breakdown
What is the process of signal transduction for Gs-coupled GPCR with the GLP-1 receptor?
Receptor activation from GLP-1 from the gut cells causes G protein activation and further signal transduction events leading to insulin secretion
What is a RTKs?
Receptor tyrosin-kinase, a membrane-spanning dimer which undergoes a conformational change leading to a phosphorylation cascade
What do RTKs use?
Phosphorylation of adaptor proteins to start signal transduction
What are adaptor proteins?
Proteins that contain a variety of protein-binding modules that link protein-binding partners together
How do adaptor proteins work?
By communicating with other proteins in the cell
