Chapter 13: Signal Transduction Pathways Flashcards
Most signal molecules:
bind to membrane receptors and transmit information across a membrane without traversing the membrane.
Examples of second messengers include:
- cAMP
- Calcium ion
- Diacyl Glycerol
Advantages of second messengers include that:
- the signal can be amplified by making many second messengers.
- second messengers can freely diffuse to other sites within the cell.
- a few common second messengers can be used in multiple signaling pathways.
Which of the following amino acids can be phosphorylated?
tyrosine, serine, threonine
Which form of the guanyl nucleotide is bound in the unactivated state?
GDP
The mechanism by which insulin-signaling processes might be terminated include:
Protein dephosphorylation by phosphatases.
How does the binding of a hormone to receptor activate a G-protein?
It causes an exchange of GTP for bound GDP.
Example(s) of disease(s) caused by altered G-protein activity include:
whooping cough and cholera
When insulin binds to its receptor, which of the following occurs?
A PIP2-dependent kinase is activated.
Define: Primary Messenger
Message received by the cell
Define: Second Messenger
Intracellular chemical that relays message from ligand receptor complex
Define: G-Protein coupled receptor
Composed of seven transmembrane helices
Define: Heterotrimeric G-Protein
Activated by 7TM Receptor
Define: G(as)
Activates adenylate cyclase
Define: Protein kinase A
Stimulated by cAMP
Define: cAMP Phosphodiesterase
Results in the inactivation of protein kinase A
Define: GTPase activity
Results in the reassociation of G(alpha) and G(beta theta).
Define: Cholera
Due to persistent stimulation of G(as)
Define: Pertussis
Results from G(as) inhibition
Define: Phospholipase C
Generates two second messengers
Define: G(aq)
Activates phospholipase C
Define: Inositol Trisphosphate
Activates Ca2+ channel
Define: Protein Kinase C
Activated by diacylglycerol
What are the three major classes of membrane receptors?
- G-Protein coupled Receptors
- Receptors that dimerize on ligand binding and recruit tyrosine kinases
- Receptors that dimerize on ligand binding that are tyrosine kinases
Explain how a small number of hormones binding to the extracellular surface of a cell can have a large biochemical effect inside the cell.
The initial signal, the binding of the hormone by a receptor, is amplified by enzymes and channels.
What are some of the structural features common to all membrane-bound receptors?
The receptor must have a site on the extracellular side of the membrane to which the signal molecule can bind and must have an intracellular domain. Binding of the signal to the receptor must induce structural changes on the intracellular domain so that the signal can be transmitted.
Why is the GTPase activity of G proteins crucial to the proper functioning of a cell?
The GTPase activity terminates the signal. Without such acitivity, after a pathway has been activated, it remains activated and is unresponsive to changes in the initial signal.
In an experiment on the nature of receptor tyrosine kinase signaling, a gene was synthesized that encoded a chimeric receptor - the extracellular part came from the insulin receptor, and the membrane-spanning and cytoplasmic parts came from the EGF receptor. The striking result was that the binding of insulin induced tyrosine kinase activity, as evidenced by rapid autophosphorylation.
What does this result tell you about the signaling mechanisms of the EGF and insulin receptors?
The insulin receptor and the EGF receptor employ a common mechanism of signal transmission across the plasma membrane.
A mutated form of the alpha-sub-unit of the heterotrimeric G protein has been identified; this form readily exchanges GDP for GTP even in the absence of an activated receptor.
What would be the effect on signaling pathway containing the mutated alpha-sub-unit.
The mutated alpha-sub-unit would always be in the GTP form and, hence, in the active form, which would stimulate its signaling pathway.
Glucose is mobilized for ATP generation in muscle in response to epinephrine, which activates G(as). Cyclic AMP phosphodiesterase is an enzyme that converts cAMP into AMP.
How would inhibitors of cAMP phosphodiesterase affect glucose mobilization in muscle?
G(as) stimulates adenylate cyclase, leading to the generation of cAMP. This signal then leads to glucose mobilization. If cAMP phosphodiesterase were inhibited, then cAMP levels would remain high even after the termination of the epinephrine signal, and glucose mobilization would continue.
