Podcast
Questions and Answers
What is the structure of a G protein-coupled receptor (GPCR)?
What is the structure of a G protein-coupled receptor (GPCR)?
Where are the binding sites for ligands located in a GPCR?
Where are the binding sites for ligands located in a GPCR?
What effect can activated protein kinase A (pkA) have following GPCR activation?
What effect can activated protein kinase A (pkA) have following GPCR activation?
Which function is NOT associated with the phosphorylation effects of pkA?
Which function is NOT associated with the phosphorylation effects of pkA?
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Which of the following best describes GPCRs' interaction with G proteins?
Which of the following best describes GPCRs' interaction with G proteins?
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How does the phosphorylation of channel proteins affect the cell?
How does the phosphorylation of channel proteins affect the cell?
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What property do water-soluble proteins have that prevents them from easily penetrating the cell membrane?
What property do water-soluble proteins have that prevents them from easily penetrating the cell membrane?
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Which type of hormone requires a receptor on the cell membrane to exert its effects?
Which type of hormone requires a receptor on the cell membrane to exert its effects?
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Which hormone is classified as a lipid-soluble hormone?
Which hormone is classified as a lipid-soluble hormone?
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What is the function of GTPase in the context of G protein-coupled receptors?
What is the function of GTPase in the context of G protein-coupled receptors?
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What is the role of adenylate cyclase in the signaling pathway initiated by G proteins?
What is the role of adenylate cyclase in the signaling pathway initiated by G proteins?
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What is the 'off' state of the receptor characterized by?
What is the 'off' state of the receptor characterized by?
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What happens to the G protein when a peptide hormone binds to the receptor?
What happens to the G protein when a peptide hormone binds to the receptor?
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Which statement correctly describes a property of lipid-soluble hormones?
Which statement correctly describes a property of lipid-soluble hormones?
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Which of the following hormones is NOT classified as a steroid hormone?
Which of the following hormones is NOT classified as a steroid hormone?
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Which of the following is NOT a peptide hormone?
Which of the following is NOT a peptide hormone?
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What characterizes water-soluble hormones in contrast to lipid-soluble hormones?
What characterizes water-soluble hormones in contrast to lipid-soluble hormones?
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What indicates the 'on' state of the receptor?
What indicates the 'on' state of the receptor?
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Which of the following hormones is included in the list of peptide hormones?
Which of the following hormones is included in the list of peptide hormones?
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What role does GTP play in the function of the G protein?
What role does GTP play in the function of the G protein?
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Which type of receptor is primarily associated with the described G protein pathways?
Which type of receptor is primarily associated with the described G protein pathways?
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What is the consequence of the activated G protein moving along the membrane?
What is the consequence of the activated G protein moving along the membrane?
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What happens when IP3 binds to its specific receptor on the reticulum?
What happens when IP3 binds to its specific receptor on the reticulum?
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What role does calcium play in the mechanism used by oxytocin?
What role does calcium play in the mechanism used by oxytocin?
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Which enzyme is responsible for breaking down cAMP to regulate signal pathways?
Which enzyme is responsible for breaking down cAMP to regulate signal pathways?
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Where are peptide hormones, such as oxytocin, primarily located?
Where are peptide hormones, such as oxytocin, primarily located?
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Which of these is NOT a peptide hormone?
Which of these is NOT a peptide hormone?
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What initiates muscle contractions in the context of calcium signaling?
What initiates muscle contractions in the context of calcium signaling?
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What is the state of receptors for steroid hormones when activated?
What is the state of receptors for steroid hormones when activated?
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Which hormone is peptide in nature?
Which hormone is peptide in nature?
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Which mechanism prevents persistent activation of signaling pathways in cells?
Which mechanism prevents persistent activation of signaling pathways in cells?
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Which hormone is steroid in nature?
Which hormone is steroid in nature?
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What is a typical property of peptide hormones?
What is a typical property of peptide hormones?
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What is a typical property of steroid hormones?
What is a typical property of steroid hormones?
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Which enzyme activates the GPCR?
Which enzyme activates the GPCR?
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Which of the following is NOT a property of peptide hormones?
Which of the following is NOT a property of peptide hormones?
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Which hormone is primarily involved in glucose metabolism and is peptide in nature?
Which hormone is primarily involved in glucose metabolism and is peptide in nature?
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What type of receptor do steroid hormones typically interact with?
What type of receptor do steroid hormones typically interact with?
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Study Notes
Hormones
- Peptide hormones include oxytocin, insulin, glucagon, FSH, LH, GH, PTH, and ADH.
- Peptide hormones are water-soluble, hydrophilic, and large, preventing them from freely crossing the phospholipid bilayer.
- Require receptors on the cell membrane and utilize 2nd Messenger Systems (Gs, Gq, Gi).
- Steroid hormones include testosterone, estrogen, progesterone, aldosterone, cortisol, and gonadocorticoids.
- Steroid hormones are lipid-soluble, derived from cholesterol, and can pass through cell membranes to bind with intracellular receptors.
G Protein-Coupled Receptors (GPCR)
- GPCRs have a structure comprising seven transmembrane helices.
- Binding sites for ligands are external, with intracellular sites for G proteins.
- The G protein is normally bound to GDP in an inactive state; hormone binding switches it to an active state by exchanging GDP for GTP.
- Activated G proteins move along the membrane to interact with effector enzymes like adenylate cyclase.
Adenylate Cyclase and cAMP
- Activated G stimulatory (Gs) protein activates adenylate cyclase, increasing its activity.
- Adenylate cyclase converts ATP to cyclic AMP (cAMP); GTPase activity of Gs turns GTP back to GDP, deactivating the G protein.
- cAMP activates Protein Kinase A (PKA), which phosphorylates various proteins, influencing:
- Membrane permeability for ions through channel proteins.
- Metabolic pathways including glycolysis by phosphorylating enzymes.
- Gene transcription and cell proliferation via phosphorylation of transcription factors.
Calcium and Calmodulin
- Calcium ions (Ca²⁺) activate calmodulin, leading to kinase activation for downstream effects.
- This mechanism, notably used by oxytocin, enhances intracellular calcium levels to trigger contractions.
Inhibition Mechanisms
- Phosphodiesterase (PDE) breaks down cAMP to regulate signaling pathways, preventing continuous activation.
- Phospholipase C may also contribute to inhibition of pathways.
Summary of Hormone Characteristics
- Peptide hormones (e.g., oxytocin, insulin) are water-soluble and act on cell membranes.
- Steroid hormones (e.g., testosterone, cortisol) are lipid-soluble and act within the cell or nucleus.
Review Questions
- Identify peptide and steroid hormones based on their properties and roles in the body.
- Understand the mechanisms of GPCR activation and the roles of G proteins and adenylate cyclase in cellular signaling.
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Description
Test your knowledge on receptor pathways in endocrinology. This quiz covers hormone interactions and the role of G proteins in signaling. Enhance your understanding of how peptide hormones function in the body.
