Cell Test 4$$$
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What is the general purpose of signal transduction?
Conversion of an impulse or stimulus from one physical or chemical form to another This process allows cells to respond to extracellular signals.
What are the two main types of G proteins?
• Monomeric • Trimeric Monomeric G proteins are activated by GEFs that are activated by surface receptors or other proteins.
Name the four common intracellular second messengers.
• cAMP • cGMP • IP3 • DAG These second messengers transmit signals through the cytosol.
What is the role of protein kinases in signaling pathways?
Transfers terminal phosphate from ATP to specific Ser/Thr or Tyr–OH This phosphorylation regulates protein activity in cellular pathways.
What type of signaling involves hormones synthesized and secreted by signaling cells?
Endocrine Signaling These signaling molecules are transported through the circulatory system.
True or false: Autocrine signaling occurs when cells respond to signals they secrete.
TRUE Tumor cells may overproduce and respond to growth factors in autocrine signaling.
What is the function of GTPase-activating proteins (GAPs)?
Stimulates rapid Gα GTP hydrolysis to GDP This process helps deactivate G proteins.
Fill in the blank: G protein-coupled receptors (GPCRs) have _______ transmembrane domains.
seven GPCRs are the largest superfamily of proteins encoded in animal genomes.
What is the role of arrestin in G-protein coupled receptor signaling?
Phosphorylates and allosterically inhibits the G-protein coupled receptor This process leads to the deactivation of the receptor.
Describe the general mechanism of activation of effector proteins associated with GPCRs.
• Ligand binding induces receptor activation • Activated receptor binds to trimeric G protein • Gα subunit releases GDP and binds GTP • Gα activates effector enzyme This sequence of events leads to the generation of second messengers.
What is the function of calcium ions (Ca2+) in signaling?
Activates calmodulin, specific kinases (PKC), and other regulatory proteins Calcium ions act as an intracellular second messenger.
What is the dissociation constant (Kd)?
Measure of receptor affinity for its ligand It indicates how tightly a ligand binds to its receptor.
What is the effect of cAMP on protein kinase A (PKA)?
Releases active catalytic subunits This activation leads to phosphorylation of target proteins.
What type of signaling is characterized by direct contact with surface receptors?
Juxtacrine Signaling This type of signaling can also involve small conduits (gap junctions) transmitting signals.
What happens during the termination of a G-protein signaling pathway?
Gα GDP dissociates from the effector protein This process deactivates the effector and alters secondary messengers.
What is the role of guanine nucleotide exchange factors (GEFs)?
Catalyze dissociation of bound GDP and replacement by GTP This activation step is crucial for G protein signaling.
What is the primary function of phospholipase C in signaling?
Produces IP3 and DAG from PIP2 These molecules are important for generating second messengers.
What is the significance of signal amplification in cellular signaling?
Allows a small signal to produce a large cellular response This is achieved through the activation of multiple downstream signaling proteins.
What does cAMP lead to the activation of?
PKA cAMP is a secondary messenger that activates Protein Kinase A (PKA), influencing various metabolic pathways.
How does PKA affect glycogen synthesis?
• Phosphorylates-inactivates glycogen synthase (GS) This action inhibits glycogen synthesis.
What is the effect of PKA on glycogen breakdown?
• Phosphorylates-activates glycogen phosphorylase kinase (GPK) • GPK phosphorylates-activates glycogen phosphorylase This initiates glycogen breakdown through a kinase cascade.
What does GP catalyze in glycogen breakdown?
First reaction Glycogen phosphorylase (GP) is crucial for initiating the breakdown of glycogen.
What happens when cAMP levels decrease?
• Inactivates PKA • Activates phosphoprotein phosphatase (PP) This leads to stimulation of glycogen synthesis and inhibition of glycogen breakdown.
What is the role of phosphoprotein phosphatase (PP)?
• Dephosphorylates-activates glycogen synthase (GS) • Dephosphorylates-inactivates glycogen phosphorylase kinase (GPK) PP plays a key role in regulating glycogen metabolism.