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Questions and Answers
What is the primary mechanism by which JAK is activated in signal transduction?
What is the primary mechanism by which JAK is activated in signal transduction?
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Which of the following describes the role of ligand-gated ion channels in signal transduction?
Which of the following describes the role of ligand-gated ion channels in signal transduction?
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In the context of second messengers, what is the primary function of cAMP within a cell?
In the context of second messengers, what is the primary function of cAMP within a cell?
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Which enzyme is responsible for synthesizing cAMP from ATP?
Which enzyme is responsible for synthesizing cAMP from ATP?
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What is the primary action of phosphodiesterase in the context of cAMP?
What is the primary action of phosphodiesterase in the context of cAMP?
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What is the primary effect of activating cGMP-dependent protein kinase G in smooth muscle cells?
What is the primary effect of activating cGMP-dependent protein kinase G in smooth muscle cells?
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What role does phosphodiesterase (PDE) play in the signaling pathway involving cGMP?
What role does phosphodiesterase (PDE) play in the signaling pathway involving cGMP?
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How is inositol trisphosphate (IP3) produced in the cell?
How is inositol trisphosphate (IP3) produced in the cell?
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What happens upon the activation of IP3 receptors at the endoplasmic reticulum?
What happens upon the activation of IP3 receptors at the endoplasmic reticulum?
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Which of the following conditions is treated with phosphodiesterase-5 inhibitors like sildenafil?
Which of the following conditions is treated with phosphodiesterase-5 inhibitors like sildenafil?
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What role do second messengers play in signal transduction?
What role do second messengers play in signal transduction?
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Which type of receptor is found on the cell membrane?
Which type of receptor is found on the cell membrane?
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What is the primary function of the ligand in signal transduction?
What is the primary function of the ligand in signal transduction?
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Which of the following statements is true about lipophilic messengers?
Which of the following statements is true about lipophilic messengers?
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What type of receptors do hydrophilic hormones primarily bind to?
What type of receptors do hydrophilic hormones primarily bind to?
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What is meant by signal amplification in a signaling cascade?
What is meant by signal amplification in a signaling cascade?
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Which subunit of the G protein is responsible for binding GTP in its active state?
Which subunit of the G protein is responsible for binding GTP in its active state?
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What is a characteristic of hydrophilic messengers?
What is a characteristic of hydrophilic messengers?
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What initiates the signaling cascade in a signal transduction pathway?
What initiates the signaling cascade in a signal transduction pathway?
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What initiates the activation of receptor tyrosine kinases?
What initiates the activation of receptor tyrosine kinases?
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Which component of signal transduction is classified as a 'first messenger'?
Which component of signal transduction is classified as a 'first messenger'?
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What is one of the functions of the Gs proteins in G protein-coupled receptors?
What is one of the functions of the Gs proteins in G protein-coupled receptors?
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How many transmembrane helices are present in G protein-coupled receptors?
How many transmembrane helices are present in G protein-coupled receptors?
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What is the role of the β and γ subunits in the G protein complex?
What is the role of the β and γ subunits in the G protein complex?
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What is the primary role of enzyme-linked receptors?
What is the primary role of enzyme-linked receptors?
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Which of the following accurately describes ligand-gated ion channels?
Which of the following accurately describes ligand-gated ion channels?
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Study Notes
Signal Transduction Overview
- Extracellular signals are converted into intracellular signals.
- A signaling molecule (ligand) binds to a specific receptor on the target cell.
Signaling Cascade
- The binding of a ligand to a receptor activates a cascade of intracellular enzymes and molecules (second messengers).
- This cascade leads to a specific cellular response.
- Signal amplification increases the number of signaling molecules at each step of the cascade.
Receptor Types
- Cell surface receptors (membrane receptors): Located in the cell membrane.
- Intracellular receptors: Located inside the cell.
- Nuclear receptors: A type of intracellular receptor that acts inside the nucleus.
Extracellular Messengers
- Lipophilic messengers: Can pass through the cell membrane to bind to intracellular receptors.
- Hydrophilic messengers: Cannot pass through the membrane and act on membrane receptors to initiate a signal.
Intracellular Receptors
- Lipophilic hormones diffuse through the cell membrane.
- Hormones bind to receptors, forming a complex.
- The hormone-receptor complex binds to hormone-responsive elements.
- This leads to changes in gene expression.
Cell Surface Receptors
- Three types:
- G protein-coupled receptors
- Enzyme-linked receptors
- Ligand-gated ion channels
G Protein-Coupled Receptors (GPCRs)
- Seven transmembrane helices
- Binding sites for ligands in extracellular regions
- Intracellular binding site for G protein
- Ligand binding causes a conformational change in the receptor.
- Activated G protein binds GTP and dissociates.
- GTPase hydrolyzes GTP to GDP, resetting the G protein.
- Different G protein types interact with different effector molecules.
G Protein Subunits
- α subunit, binds GDP (inactive) and GTP (active state).
- β and γ subunits, stable complex with lipid anchor in the membrane.
G Protein Functions
- Gs proteins stimulate adenylyl cyclase.
- Gi proteins inhibit adenylyl cyclase.
- Gq proteins stimulate phospholipase C.
Receptor Tyrosine Kinases (RTKs)
- Extracellular domain
- Single transmembrane domain
- Intracellular domain with tyrosine kinase activity
- Ligand binding triggers dimerization and autophosphorylation of cytoplasmic tyrosine residues.
- This initiates downstream signaling cascades.
Non-receptor Tyrosine Kinases and Activation
- Membrane receptors without tyrosine kinase activity.
- Ligand binding causes receptor dimerization.
- JAK proteins phosphorylate each other.
- This initiates STAT protein activation.
- STAT dimers effect gene expression in the nucleus.
Ligand-Gated Ion Channels
- Ligand binding induces a conformational change.
- Pore opening allows ion movement across the membrane.
- Altered membrane potential leads to rapid response.
Second Messengers
- Small molecules that mediate intracellular response to extracellular stimuli.
- Examples: cAMP, cGMP, IP3, Ca2+
Cyclic AMP (cAMP)
- Synthesized from ATP by adenylyl cyclase
- Gs proteins activate adenylyl cyclase.
- Gi proteins inhibit adenylyl cyclase.
- cAMP is degraded by phosphodiesterase to AMP.
Cyclic GMP (cGMP)
- Synthesized from GTP by guanylyl cyclase.
- Activates cGMP-dependent protein kinase G.
- Mediates smooth muscle relaxation.
- Degraded by phosphodiesterase.
- PDE inhibitors used in treating pulmonary hypertension and erectile dysfunction.
Nitric Oxide (NO)
- Short half-life, diffuses across membranes.
- Synthesized in endothelial cells of blood vessels.
- Activates guanylyl cyclase, increasing cGMP and leading to vascular relaxation.
Inositol Trisphosphate (IP3)
- Second messenger released by phospholipase C's action on membrane phospholipids.
- Causes release of Calcium from the endoplasmic reticulum, raising intracellular Calcium concentration.
- This triggers smooth muscle contraction.
Calcium (Ca2+) as a Second Messenger
- Intracellular Ca2+ levels are usually low.
- Second messengers or action potentials raise Ca2+ levels, triggering various cellular responses.
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Description
This quiz covers the fundamentals of signal transduction, focusing on how extracellular signals are transformed into intracellular responses. It includes details about signaling cascades, receptor types, and different categories of extracellular messengers. Test your understanding of these essential biological processes.
