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Questions and Answers
Which small messenger molecule is generated by adenylyl cyclase?
Which small messenger molecule is generated by adenylyl cyclase?
What major response occurs in skeletal muscle when epinephrine is present?
What major response occurs in skeletal muscle when epinephrine is present?
Which enzyme does phospholipase C produce?
Which enzyme does phospholipase C produce?
What effect does an increase in cytosolic Ca2+ levels have?
What effect does an increase in cytosolic Ca2+ levels have?
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What is the role of Protein Kinase A (PKA) in cellular responses?
What is the role of Protein Kinase A (PKA) in cellular responses?
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Which of the following hormones is NOT mentioned as having a responsive role mediated by cyclic AMP?
Which of the following hormones is NOT mentioned as having a responsive role mediated by cyclic AMP?
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Which messenger molecule can lead to the release of Ca2+ from the endoplasmic reticulum?
Which messenger molecule can lead to the release of Ca2+ from the endoplasmic reticulum?
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Which G protein target generates cAMP?
Which G protein target generates cAMP?
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What triggers the increase in cytosolic calcium levels in an egg during fertilization?
What triggers the increase in cytosolic calcium levels in an egg during fertilization?
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What is the role of DAG in the fertilization process?
What is the role of DAG in the fertilization process?
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Which type of receptor is primarily responsible for activating Ras?
Which type of receptor is primarily responsible for activating Ras?
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What cellular effect does Ras stimulate?
What cellular effect does Ras stimulate?
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What is the result of aberrant signaling in cellular pathways?
What is the result of aberrant signaling in cellular pathways?
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What class of receptors does PKC activation lead to new protein synthesis upon fertilization?
What class of receptors does PKC activation lead to new protein synthesis upon fertilization?
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Which of the following statements about receptor tyrosine kinases (RTKs) is correct?
Which of the following statements about receptor tyrosine kinases (RTKs) is correct?
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What does IP3 do in the fertilization process?
What does IP3 do in the fertilization process?
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What percentage of human cancers have activating mutations in Ras?
What percentage of human cancers have activating mutations in Ras?
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Which signaling pathway is associated with cell proliferation upon Ras activation?
Which signaling pathway is associated with cell proliferation upon Ras activation?
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What is the primary function of ion-channel-coupled receptors?
What is the primary function of ion-channel-coupled receptors?
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How does phospholipase C (PLC) function in cell signaling?
How does phospholipase C (PLC) function in cell signaling?
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What characterizes G-protein-coupled receptors (GPCRs)?
What characterizes G-protein-coupled receptors (GPCRs)?
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What happens to the G-protein alpha subunit after it is activated?
What happens to the G-protein alpha subunit after it is activated?
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Which signaling molecules can activate G-protein-coupled receptors?
Which signaling molecules can activate G-protein-coupled receptors?
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What is a common target of activated G proteins?
What is a common target of activated G proteins?
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What is the main outcome when a GPCR is deactivated?
What is the main outcome when a GPCR is deactivated?
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Which of the following describes a characteristic of GPCRs?
Which of the following describes a characteristic of GPCRs?
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What unique structural feature do all GPCRs share?
What unique structural feature do all GPCRs share?
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What role do second messengers like Ca2+ and DAG play in cell signaling?
What role do second messengers like Ca2+ and DAG play in cell signaling?
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Which of the following statements is true regarding G-proteins?
Which of the following statements is true regarding G-proteins?
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What is a potential consequence of mutations in G-protein signaling pathway proteins?
What is a potential consequence of mutations in G-protein signaling pathway proteins?
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What type of drugs are predominantly directed at GPCRs based on current pharmaceutical practices?
What type of drugs are predominantly directed at GPCRs based on current pharmaceutical practices?
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Study Notes
Cell Signaling II
- Cell surface receptors include ion-channel-coupled receptors, G-protein-coupled receptors (GPCRs), and enzyme-coupled receptors.
- GPCRs activate trimeric G proteins.
- Phospholipase C (PLC) is activated by GPCRs and mediates signal transduction.
- Second messengers, such as IP₃, DAG, and Ca²⁺, are involved in signal transduction.
Cell Surface Receptors
- Cell surface receptors relay extracellular signals via intracellular signaling pathways.
- Two major types of receptors: intracellular (steroid hormones) and cell surface.
- Types of cell-surface receptors: ion-channel-coupled, G-protein-coupled, and enzyme-coupled.
Ion-channel Coupled Receptors
- Cause changes in plasma membrane permeability to specific ions, altering membrane potential.
- Respond very rapidly, within milliseconds.
- Important in nerve cells.
G-Protein Coupled Receptors (GPCRs)
- A large class of receptors (>700 in humans) activated by various signaling molecules.
- GPCR structure is conserved. They are 7-pass transmembrane proteins.
- G proteins have three subunits (α, β, γ). Signal binding causes a conformational change in the receptor.
- Activated Gα and Gβγ activate different effector proteins.
- Activated receptor acts as a GEF for its G-protein.
- G-protein subunit GTP hydrolysis inactivates it and reassembles with βγ.
- Mutations in signaling pathway proteins can produce constant 'ON' states (e.g., constitutive activation of an α-subunit).
Two Major Targets of GPCRs
- Phospholipase C (PLC): produces lipids.
- Adenylyl cyclase: generates cAMP; activates PKA.
- Cellular responses resulting from these pathways.
Example Cellular Responses Mediate Cyclic AMP
- Epinephrine, heart—increase in heart rate and force of contraction.
- Epinephrine, skeletal muscle—glycogen breakdown.
- Epinephrine/glucagon, fat—fat breakdown.
- Adrenocorticotropic hormone (ACTH), adrenal gland—cortisol secreation.
Phospholipase C (PLC)
- IP₃ production leads to Ca²⁺ release from the endoplasmic reticulum, increasing cytosolic Ca²⁺ concentration.
- DAG, in combination with Ca²⁺, activates protein kinase C (PKC).
Example Cellular Responses Mediate by Phospholipase C (PLC) Activation
- Vasopressin, liver—glycogen breakdown.
- Acetylcholine, pancreas—secretion of amylase.
- Acetylcholine, smooth muscle—contraction.
- Thrombin, blood platelets—aggregation.
Enzyme-Coupled Receptors
- Receptors acting as enzymes.
- Receptors associate with enzymes.
- Examples: Receptor Tyrosine Kinases (RTKs).
Receptor Tyrosine Kinases (RTKs)
- Large class of enzyme-coupled receptors.
- Activated by growth factors (FGF, EGF).
- Cytoplasmic domains function as tyrosine protein kinases.
- Involved in regulating growth and proliferation.
- RTKs frequently activate the small GTPase Ras.
Ras
- Plays a significant role in cell proliferation, often via the MAP-kinase pathway.
Signaling Pathways
- Signaling pathways can be complex and highly interconnected.
- Aberrant signaling (always 'ON') can have pathological consequences.
Pattern Formation in Drosophila Embryo
- A specialized area of study using the fruit fly as a model organism.
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Description
Test your knowledge on various types of cell surface receptors, specifically focusing on ion-channel-coupled receptors and G-protein-coupled receptors (GPCRs). This quiz covers the mechanisms of signal transduction and the role of second messengers like IP₃, DAG, and Ca²⁺. Challenge yourself to understand these crucial components of cell signaling.
