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Questions and Answers
What role does adenylyl cyclase play in cellular signaling?
What role does adenylyl cyclase play in cellular signaling?
- It regulates gene expression directly.
- It fragments proteins for degradation.
- It transmits signals through ion channels.
- It converts ATP to cyclic AMP. (correct)
How does cyclic AMP (cAMP) contribute to cellular responses?
How does cyclic AMP (cAMP) contribute to cellular responses?
- By phosphorylating lipids in the cell membrane.
- By inhibiting G protein activation.
- By directly altering the cell's membrane potential.
- By activating protein kinase A, which then phosphorylates other proteins. (correct)
Which of the following statements best describes the function of protein kinase A in the signaling pathway?
Which of the following statements best describes the function of protein kinase A in the signaling pathway?
- It phosphorylates proteins to elicit a cellular response. (correct)
- It initiates the formation of G proteins.
- It directly stimulates adenylyl cyclase activity.
- It acts as a second messenger itself.
What is the primary function of GPCRs in cellular signaling?
What is the primary function of GPCRs in cellular signaling?
What mechanism ensures signal amplification in the pathway involving cyclic AMP?
What mechanism ensures signal amplification in the pathway involving cyclic AMP?
What characteristic of receptors allows them to be activated by varying ligand concentrations?
What characteristic of receptors allows them to be activated by varying ligand concentrations?
Which of the following is the primary function of adenylyl cyclase in hormone signaling?
Which of the following is the primary function of adenylyl cyclase in hormone signaling?
How does cyclic AMP (cAMP) function as a second messenger in cellular signaling?
How does cyclic AMP (cAMP) function as a second messenger in cellular signaling?
What is the role of Protein Kinase A (PKA) in response to cAMP?
What is the role of Protein Kinase A (PKA) in response to cAMP?
Which scenario best demonstrates signal amplification in cells?
Which scenario best demonstrates signal amplification in cells?
Which characteristic of intracellular receptors allows them to respond to hydrophobic hormones?
Which characteristic of intracellular receptors allows them to respond to hydrophobic hormones?
What happens when there is a saturation of receptors by a hormone in the cell?
What happens when there is a saturation of receptors by a hormone in the cell?
What distinguishes hormonal signaling from neural signaling?
What distinguishes hormonal signaling from neural signaling?
What connects the cytoplasmic tail of G protein-coupled receptors (GPCRs) to the G protein?
What connects the cytoplasmic tail of G protein-coupled receptors (GPCRs) to the G protein?
Which of the following is a role of G proteins when activated?
Which of the following is a role of G proteins when activated?
What is the primary role of adenylyl cyclase in the signal transduction pathway?
What is the primary role of adenylyl cyclase in the signal transduction pathway?
How does cAMP function as a second messenger in the signaling pathway?
How does cAMP function as a second messenger in the signaling pathway?
Which component is essential for the amplification of the signal in the GPCR-adenylyl cyclase pathway?
Which component is essential for the amplification of the signal in the GPCR-adenylyl cyclase pathway?
What happens to protein kinase A after it is activated by cAMP?
What happens to protein kinase A after it is activated by cAMP?
What is a key characteristic of G protein-coupled receptors (GPCRs) in terms of their structure?
What is a key characteristic of G protein-coupled receptors (GPCRs) in terms of their structure?
Which lipid second messenger is commonly associated with GPCR signaling pathways?
Which lipid second messenger is commonly associated with GPCR signaling pathways?
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Study Notes
G Protein-Coupled Receptors (GPCRs)
- Membrane-spanning proteins with a cytoplasmic tail linked to a three-part G protein.
- The G protein-coupled adenylyl cyclase-cAMP system is a common signal transduction pathway for many protein hormones.
- Utilize lipid second messengers like diacylglycerol (DAG) and inositol trisphosphate (IP3).
- Activated G proteins open ion channels in the membrane and alter enzyme activity on the cytoplasmic side.
- Gs protein activates adenylyl cyclase.
Adenylyl Cyclase and cAMP Pathway
- G protein activation triggers adenylyl cyclase, an amplifier enzyme.
- Adenylyl cyclase converts ATP to cyclic AMP (cAMP).
- cAMP activates protein kinase A.
- Protein kinase A phosphorylates other proteins, leading to a cellular response.
- cAMP acts as a second messenger, amplifying the target cell's response.
Hormone Signaling
- Hormone binding to a receptor changes the receptor's conformation and activity.
- This alters intracellular signaling pathways.
- Results in changes in target protein synthesis or modification of existing proteins.
Receptor Characteristics
- Receptors are large proteins, often belonging to families.
- A single ligand may have multiple receptors, and a single receptor may bind multiple ligands.
- The number of receptors per target cell can vary widely (500-100,000).
- Receptors can be activated and inhibited.
- Locations include the cell membrane, cytoplasm, and nucleus.
- Receptors display high affinity, saturability, specificity, and reversibility.
Receptor Saturation
- A graph showing the relationship between bound labeled testosterone and total labeled testosterone demonstrates receptor saturation. At a certain point increasing hormone concentration no longer increases the response.
Example of Receptor Saturation
- Hormone A binding to receptor B causes response C. Doubling hormone A concentration doubles response C. However, further doubling hormone A has no effect on response C due to receptor saturation
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