Chapter 15 Flashcards
(40 cards)
What are the types of extracellular signaling?
1) autocrine- cell has receptors on its surface that respond to the messenger
2) paracrine- messenger molecules travel short distances through extracellular space
3) endocrine- messenger molecules reach their target cells through the bloodstream
What are two ways that cell signaling systems work (generally)?
1) Some cell surface receptors generate an intracellular second messenger through an enzyme called an effector
2) Surface receptors recruit proteins to their intracellular domains at the plasma membrane
What are some ways that protein phosphorylation can change protein behavior?
1) Activate or inactivate an enzyme
2) Increase or decrease protein-protein interactions
3) Change the sub cellular location of the protein
4) Trigger protein degradation
What are G protein coupled receptors?
constitute the single largest superfamily of proteins encoded by animal genomes
What are some natural ligands of GPCRs?
hormones, neurotransmitters, opium derivatives, chemoattractants (odorants, tastants, and photons)
What are the steps in termination of the response?
1) Desensitization by blocking active receptors from turning on additional G proteins
2) G protein-coupled receptor kinase (GRK) activates a GPCR via phosphorylation
3) Proteins called arresting compete with G proteins to bind GPCRs
4) Termination of the response is accelerated by regulators of G protein signaling (RGSs)
What are the steps in arrestin-mediated internalization of GPCRs?
1) Phosphorylation of the GPCRs sets the stage for the binding of arrestins, which compete for binding with the G proteins
2) Upon binding, the GPCRs become desensitized, even though ligands are bound extracellularly.
3) If receptors are recycled and returned to the cell surface, the cells remain sensitive to the ligand and are said to be resensitized.
What do b adrenergic receptors stimulate?
Gas to activate adenylate cyclase
What is the target of the cholera toxin?
Gas, pathway locked in stimulatory state causing diarrhea.
What do a adrenergic receptors stimulate?
Gai to inhibit adenylate cyclase.
What is the target of pertussis toxin?
Gai, locks in inhibitory state causing excessive coughing
What is Cyclic AMP?
Second messenger, which is released into the cytoplasm after the binding of a ligand.
- amplify the response to a single extracellular ligand.
What produces the secondary messengers IP3 and DAG?
Phophatidylinositol-specific phospholipase C-beta
What does DAG do?
Activates protein kinase C, which phosphorylates serine and threonine residues on target proteins
What forms PH domains?
Phosphorylated phosphoinositides form the lipid-binding domains
What synthesized cAMP?
adenylyl cyclase
What does cAMP do?
1) evokes a reaction cascade that leads to glucose mobilization
2) cAMP molecules diffuse into the cytoplasm where they bind a cAMP-dependent protein kinase (PKA)
What do PKA molecules do?
phosphorylate nuclear proteins (which regulate gene expression)
What halts the reaction cascade?
Phosphatases
What limits the production of cAMP?
external stimulus
Describe the mechanism for signal transduction through protein tyrosine phosphorylation:
1) Results from ligand binding
2) Tyrosine kinase phosphorylates another subunit of the receptor (autophosphorylation)
3) RTKs phosphorylate tyrosines within phosphotyrosine motifs
Describe the Ras-MAP kinase pathway:
1) Ras is active when bound to GTP and inactive when bound to GDP
2) GTPase-activating proteins (GAPs) shorten the active time of Ras
3) Guanine nucleotide-exchange factors (GEFs) stimulate the exchange of GDP for GTP
4) Guanine nucleotide-dissociation inhibitors (GDIs) inhibit release of GDP
What is the Ras-MAP kinase cascade?
a cascade of enzymes resulting in activation of transcription factors
What are the steps in glucose transport?
1) PKB regulates glucose uptake by GLUT4 transporters
2) GLUT4 transporters reside in intracellular membrane vesicles
3) Vesicles fuse with the membrane in response to ligand binding to the IR
