Podcast
Questions and Answers
What are ligands?
The signaling molecules that bind to specific receptors.
Which of the following are types of intercellular signaling?
Match the types of signaling with their descriptions:
Contact dependent signaling = Requires direct membrane contact Paracrine signaling = Acts on neighboring cells via local mediators Synaptic signaling = Transmits signals electrically along axons Endocrine signaling = Secretes hormones into the bloodstream
Autocrine signaling involves a cell that releases the signal being the target.
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What happens if appropriate survival signals are deprived?
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What type of receptors are mostly transmembrane proteins?
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What type of ligands can directly diffuse through the plasma membrane?
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What role do effector proteins play in cell signaling?
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Which type of intercellular signaling requires direct contact between cells?
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What is a common consequence of errors in cellular information processing?
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What defines the signaling process referred to as 'paracrine signaling'?
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What is the primary function of receptors in cell signaling?
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How do intracellular signaling pathways typically begin?
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In the context of signaling pathways, what is meant by 'signal transduction'?
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Which type of signaling is characterized by neurons transmitting signals along axons?
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What triggers the release of calcium ions from the endoplasmic reticulum?
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Which of the following processes is NOT triggered by an increase in intracellular calcium concentration?
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How do internal receptors influence gene expression?
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What is one of the main roles of Protein Kinase C (PKC) in the cell?
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Which statement best describes calcium ions as second messengers?
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What is the outcome of the conformational change in the internal receptor upon ligand binding?
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In what way does the ligand-receptor complex influence transcription?
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What is the role of IP3 in cellular signaling?
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Which hormone utilizes cAMP as a second messenger to initiate cellular responses?
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What enzyme synthesizes cyclic AMP (cAMP) from ATP?
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Which of the following second messengers is produced from GTP?
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Diacylglycerol (DAG) acts via which protein kinase?
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What is one of the primary roles of cyclic AMP (cAMP) in cellular signaling?
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What molecule is primarily hydrolyzed by phospholipase C to produce DAG and IP3?
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Which molecule directly activates Protein Kinase G (PKG)?
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What is one common effect of the action of cyclic GMP (cGMP)?
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What is the primary role of endocrine cells in intercellular signaling?
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Which type of signaling requires the signal-producing cell to also be the target cell?
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What is a defining feature of water-soluble ligands?
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What happens to a cell if it is deprived of appropriate survival signals?
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Which type of receptor requires the signaling molecule to be small and capable of diffusing across the plasma membrane?
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Which class of ligands is characterized by their ability to diffuse directly through the plasma membrane?
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Which statement about nitric oxide (NO) is accurate?
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Which of the following types of signaling molecules are considered small hydrophobic ligands?
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What occurs to the α subunit of a G protein after GTP hydrolysis?
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Which of the following best describes the action of the Gi protein in heart muscle cells?
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What is the primary role of second messengers like cAMP and Ca++ in cell signaling?
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How do enzyme-linked receptors like tyrosine kinases transmit signals?
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Which G protein is associated with the epinephrine receptor and stimulates adenyl cyclase?
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What happens to intracellular signaling molecules upon activation of cell surface receptors?
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What is one of the effects of βγ subunits from Gi proteins in heart muscle cells?
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Which is a characteristic of water-soluble second messengers like cAMP?
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Study Notes
### Cell Signaling
- Cellular communication is essential for development, tissue repair, and immunity.
- Errors in cellular communication contribute to various diseases, such as cancer, autoimmune disorders, and diabetes.
- Understanding cell signaling can lead to more effective disease treatments and the creation of artificial tissues.
Definitions
- Signaling refers to cell-to-cell communication through signals.
- Signal transduction is the process of translating extracellular signals into intracellular responses.
- A ligand is the signaling molecule.
- Receptors bind to specific ligands and activate intracellular pathways.
- Intracellular signaling proteins process and transmit the signal to target proteins.
- Effector proteins are the targets at the end of signaling pathways.
Intracellular Signaling Pathway
- Extracellular signal molecules bind to receptor proteins on the cell membrane.
- Activated receptors initiate intracellular signaling pathways involving a series of signaling proteins.
- Intracellular signaling proteins modify the activity of effector proteins, altering cell behavior.
Intercellular Signaling
- Cells communicate through extracellular messenger molecules.
- Contact-dependent signaling requires direct membrane-membrane contact between cells.
- Paracrine signaling involves local mediators released into the extracellular space, affecting nearby cells.
- Synaptic signaling is specific to neurons, transmitting signals electrically along axons and releasing neurotransmitters at synapses.
- Endocrine signaling relies on endocrine cells that secrete hormones into the bloodstream for widespread distribution.
- Autocrine signaling occurs when the signaling cell is also the target cell.
Cellular Response
- Cells respond to specific combinations of extracellular signals.
- Cells may require multiple signals for survival, growth, division, or differentiation.
- Deprivation of survival signals triggers apoptosis (programmed cell death).
Extracellular Signal Molecules and Receptors
- Extracellular signal molecules include proteins, small peptides, amino acids, nucleotides, steroids, retinoids, fatty acid derivatives, NO, and CO.
- Target cells respond through receptors.
- Receptors are transmembrane proteins on the cell surface or intracellular proteins.
Receptor Types
- Transmembrane receptors bind extracellular ligands and activate intracellular signaling pathways.
- Intracellular receptors bind to small, hydrophobic ligands that can diffuse across the plasma membrane.
Types of Signaling Ligands
- Small hydrophobic ligands diffuse across the plasma membrane and bind to intracellular receptors, such as steroid hormones.
- Other ligands include gases like nitric oxide (NO) that directly cross the plasma membrane.
- Water-soluble ligands bind to transmembrane receptors on the cell surface.
Cell Signaling
- It is a complex system of communication regulating basic cellular activities and coordinating actions.
- Allows cells to perceive and respond to their microenvironment, crucial for processes like development, tissue repair, immunity, and homeostasis.
- Errors in cellular information processing can cause diseases like cancer, autoimmunity, and diabetes.
- Understanding cell signaling can lead to effective disease treatment and potential artificial tissue creation.
Definitions
- Signaling: Cell-cell communication via signals
- Signal Transduction: Process of converting extracellular signals into intracellular responses
- Ligand: The signaling molecule
- Receptors: Bind specific ligands and initiate intracellular pathways
- Intracellular Signaling Proteins: Process signals and transmit them to intracellular targets
- Effector Proteins: Targets at the end signaling pathways, altering the cell's behavior.
Intracellular Signaling Pathway
- Signal molecule binds to a receptor protein on the target cell's membrane (PM).
- Receptor activates intracellular signaling pathways, involving a series of signaling proteins.
- Intracellular signaling proteins change the activity of effector proteins, influencing cellular behavior.
Four Forms of Intercellular Signaling
- Contact-Dependent Signaling: Requires direct contact between cells. Important in development and immune responses.
- Paracrine Signaling: Local mediators released into the extracellular space act on nearby cells. Important for nerve-muscle communication.
- Synaptic Signaling: Neurons transmit electrical signals along axons and release neurotransmitters at synapses.
- Endocrine Signaling: Endocrine cells secrete hormones into the bloodstream for distribution throughout the body.
- Autocrine Signaling: The cell that releases the signal is also the target.
Response to Signals
- Each cell responds to specific combinations of extracellular signals.
- Cells require multiple signals to survive, grow, divide, or differentiate.
- Deprivation of survival signals leads to apoptosis (programmed cell death).
Extracellular Signal Molecules
- Bind to specific receptors.
- Include proteins, peptides, amino acids, nucleotides, steroids, retinoids, fatty acid derivatives, NO, CO.
Receptors
- Transmembrane Proteins: Located on the target-cell surface, bind to extracellular molecules (ligands) and act as signal transducers, generating intracellular signals that alter the cell's behavior.
- Intracellular Receptors: Ligands must be small enough to diffuse across the plasma membrane and bind to receptors inside the cell, either in the cytosol or nucleus.
Types of Signaling Ligands
- Small Hydrophobic Ligands: Diffuse across the plasma membrane and interact with internal receptors. Steroid hormones are an important example.
- Other Ligands: Include nitric oxide (NO), which diffuses across the plasma membrane and interacts with receptors in smooth muscle.
- Water-Soluble Ligands: Polar molecules that cannot pass through the plasma membrane unaided. Instead, they bind to extracellular receptors.
G Protein-Coupled Receptor
- Activate intracellular signaling pathways via the activation of G proteins.
- G proteins activate adenyl cyclase, which converts ATP to the second messenger cAMP.
cAMP Dependent Pathway
- Activated by the binding of epinephrine to a receptor, leading to the activation of adenyl cyclase.
- Gs (stimulatory) and Gi (inhibitory) G proteins activate adenyl cyclase or inhibit it, respectively.
- cAMP can also activate a protein kinase A (PKA) or directly influence transcription.
Enzyme-Linked Receptors
- Tyrosine kinase receptors are a prominent example.
- Signaling molecules bind to the extracellular domains of two nearby receptors, causing dimerization.
- The tyrosine kinase receptor phosphorylates tyrosine residues on intracellular domains, triggering signal transmission.
- Important for cell growth, differentiation, and other processes.
Intracellular Signaling Molecules
- Relay signals received by cell surface receptors into the cell interior.
- Includes small molecules (second messengers), like cAMP, Ca++, and diacylglycerol (DAG), and proteins.
- Proteins can act as molecular switches, activated or deactivated by phosphorylation.
Second Messengers
- Cyclic Nucleotides: cAMP and cGMP.
- Inositol Trisphosphate (IP3) & Diacylglycerol (DAG): Produced by the hydrolysis of PIP2.
- Calcium Ions (Ca2+): Released by IP3 from the endoplasmic reticulum.
Cyclic AMP (cAMP)
- Synthesized from ATP by adenylyl cyclase.
- Activated by hormones that bind to receptors that activate G proteins, in turn activating adenylyl cyclase.
- Activates Protein Kinase A (PKA), which phosphorylates target proteins to regulate cellular activities. It can also influence gene transcription.
Cyclic GMP (cGMP)
- Synthesized from GTP by guanylyl cyclase.
- Serving as a second messenger for ANP and NO.
- Activates Protein Kinase G (PKG), which phosphorylates target proteins.
Inositol Trisphosphate & Diacylglycerol
- Produced by the action of phospholipase C (PLC) on PIP2.
- IP3: Diffuses and binds receptors of the endoplasmic reticulum to release Ca2+ into the cytosol.
- DAG: Recruits Protein Kinase C (PKC), a calcium-dependent kinase, to phosphorylate proteins and regulate cellular processes.
Calcium Ions (Ca2+)
- Widely used as an intracellular messenger.
- Trigger various cellular events like muscle contraction, exocytosis, activation of lymphocytes, apoptosis, and biochemical changes mediated by PKC.
Internal Receptors
- Found in the cytoplasm.
- Respond to hydrophobic ligand molecules that can cross the plasma membrane.
- Bind to proteins that regulate mRNA synthesis to control gene expression.
Gene Expression Regulation
- Internal receptors influence gene expression by regulating transcription.
- Ligand binding exposes a DNA-binding site, and the complex moves into the nucleus to bind specific regulatory regions on DNA, promoting transcription.
- Internal receptors directly affect gene expression without relying on other receptors or messengers.
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Description
Explore the essential concepts of cell signaling, a crucial process for cellular communication involved in development, tissue repair, and immunity. This quiz covers defined terms such as signaling, signal transduction, and the roles of ligands, receptors, and effector proteins in intracellular pathways. Understanding these concepts is key to grasping their implications in diseases like cancer and diabetes.
