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Questions and Answers
In bacteria, what does 'quorum sensing' refer to?
Quorum sensing refers to the ability of bacteria to sense their population density through signaling molecules and coordinate their behavior accordingly.
What is the difference between endocrine and neuroendocrine signaling?
Endocrine signaling involves hormones traveling through the bloodstream to target distant organs, while neuroendocrine signaling involves the release of hormones from neurons into the blood.
Is chemical synaptic signaling an example of autocrine or paracrine signaling? Explain.
Chemical synaptic signaling is an example of paracrine signaling.
What are connexins and connexons?
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How is it possible for us to enjoy apples in NYC in the spring when apples are harvested in early fall? How are apples stored?
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Design an experiment to determine whether the protein β-glucosidase is as effective as a chewing caterpillar of Pieris brassicae in eliciting a defense response from cabbage plants.
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Design an experiment to determine whether the signal that warns neighboring plants about herbivore attacks is plant volatiles or the sound of chewing.
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According to Sutherland, when a cell receives an external signal, what three processes occur?
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Why is there no receptor in the plasma membrane for a steroid hormone?
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Explain what is happening in the ligand-gated ion channel receptor.
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List the steps for a receptor tyrosine kinase to carry out its function from signal reception to cellular response.
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Why is it important for the alpha subunit of the G protein to function as a GTPase enzyme?
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Define what a first messenger and a second messenger are.
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Why is it important for the Ca2+ pumps to reduce the concentration of Ca2+ in the cytosol?
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Which one of the following is a common second messenger?
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Explain what kinases and phosphatases do.
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Where is the substrate for the reaction carried out by phospholipase C coming from? What are the products of the reaction?
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Identify the first and second messengers in the pathway activated by hormone attachment to a receptor leading to activation of PKC.
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During the termination process of receptor activation, what are two possible ways to deactivate the receptor?
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Study Notes
Cell Communication
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Quorum sensing in bacteria refers to the ability of bacteria to sense the density of their population and coordinate their behavior accordingly. Bacteria communicate using chemical signals and respond to changes in population density to control gene expression.
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Endocrine signaling involves hormones that are secreted by specialized cells and travel through the bloodstream to act on distant target cells. Neuroendocrine signaling is a specialized form of endocrine signaling where hormones are released from neurons and travel through the bloodstream to act on target cells.
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Chemical synaptic signaling is an example of paracrine signaling. In this type of signaling, a neurotransmitter is released from a neuron and acts on nearby target cells within a synapse.
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Connexins are proteins that form channels called connexons. These channels allow for direct communication between cells in animal tissues.
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Gap junctions in animal cells and plasmodesmata in plant cells allow for direct movement of signaling molecules between cells. Gap junctions connect adjacent cells by forming channels made up of connexon complexes. Plasmodesmata are membrane-lined channels that connect adjacent plant cells, allowing for the passage of water, nutrients, and signaling molecules.
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Apples are stored in a controlled atmosphere with low oxygen and high carbon dioxide levels, which slows down the rate of respiration and inhibits the production of ethylene. This process allows for the preservation of the apples and delays their ripening process. Ethylene gas can trigger the ripening of fruits, including apples.
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Experiment to determine whether the protein -glucosidase is as effective as a chewing caterpillar of Pieris brassicae in eliciting a defense response from cabbage plants through release of plant volatiles:
- Control group: Cabbage plants that are not exposed to any treatments.
- Treatment group 1: Cabbage plants that are exposed to -glucosidase enzyme.
- Treatment group 2: Cabbage plants that are exposed to chewing caterpillars of Pieris brassicae.
- Independent variable: The type of treatment (-glucosidase or caterpillar)
- Dependent variable: The amount of plant volatiles released by the cabbage plants.
- Quantitative data: Measure the concentration of plant volatiles released by each treatment group using a gas chromatograph.
- Qualitative data: Observe the visible signs of defense response in each treatment group, such as changes in leaf color or shape.
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Experiment to determine whether the signal that warns the neighboring plants about the imminent herbivore attack is a) the plant volatiles released from the plants that are being chewed by the insects, or b) the sound of chewing.
- Control group: Cabbage plants that are not exposed to any treatments or sounds.
- Treatment group 1: Cabbage plants that are exposed to chewing caterpillars of Pieris brassicae (without any sound isolation).
- Treatment group 2: Cabbage plants that are exposed to the sound of caterpillar chewing but are isolated from any plant volatiles released by the caterpillars.
- Independent variable: The type of stimulus (plant volatiles or sound of chewing).
- Dependent variable: The amount of plant volatiles released by the nearby plants.
- Quantitative data: Measure the concentration of plant volatiles released by each treatment group using a gas chromatograph.
- Qualitative data: Observe the visible signs of defense response in each treatment group, such as changes in leaf color or shape.
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According to Sutherland, when a cell receives an external signal, it goes through three processes:
- Reception: The binding of the signal molecule to a receptor.
- Transduction: Conversion of the signal into a form that can trigger a specific cellular response.
- Response: The specific cellular action that occurs as a result of the signal.
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Steroid hormones are lipid-soluble molecules that can pass directly through the plasma membrane. They bind to receptors inside the cell, usually in the cytoplasm or nucleus. The hormone-receptor complex then acts as a transcription factor to regulate gene expression.
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Ligand-gated ion channel receptors are transmembrane proteins that act as gated channels for specific ions. When a ligand (signaling molecule) binds to the receptor, a conformational change occurs, opening the channel and allowing specific ions to flow across the membrane. This results in a change in the membrane potential and can trigger downstream signaling pathways.
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Activation of receptor tyrosine kinases (RTKs):
- Reception: The signal molecule (ligand) binds to the extracellular domain of the RTK.
- Dimerization: The binding of the ligand causes two RTK molecules to come together.
- Autophosphorylation: The dimerized RTKs phosphorylate each other on tyrosine residues within the cytoplasmic domains.
- Signaling protein activation: The phosphorylated tyrosine residues act as docking sites for other signaling proteins. These proteins can bind to the phosphorylated RTK and become activated, leading to downstream signaling pathways.
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G-Protein coupled receptors (GPCRs): GPCRs are transmembrane proteins that associate with G proteins, which are trimeric proteins comprised of alpha, beta, and gamma subunits. When a ligand binds to the GPCR, the receptor undergoes a conformational change. The activated GPCR interacts with the G protein, causing the alpha subunit to release GDP and bind to GTP. The alpha subunit then dissociates from the beta and gamma subunits and can activate other signaling proteins.
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The alpha subunit of the G protein acts as a GTPase enzyme to hydrolyze its bound GTP to GDP. This step is crucial for terminating the signal. When GTP is hydrolyzed to GDP, the alpha subunit reassociates with the beta and gamma subunits, turning the G protein off and allowing the signal transduction pathway to return to its inactive state.
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A first messenger is the extracellular signaling molecule that binds to a receptor on the cell surface. A second messenger is an intracellular signaling molecule that is generated in response to the first messenger and relays the signal to downstream targets.
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The Ca2+ pump is a protein that pumps Ca2+ ions out of the cytosol and into the extracellular space or into intracellular compartments. This process is crucial for maintaining a low Ca2+ concentration in the cytosol. The Ca2+ gradient is essential for various cellular processes, including muscle contraction, neuronal signaling, and cell division.
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cAMP is a common second messenger.
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Kinases are enzymes that add phosphate groups to target proteins, a process called phosphorylation. This can activate or deactivate proteins, depending on the specific protein involved. Phosphatases are enzymes that remove phosphate groups from target proteins, a process called dephosphorylation. This can also activate or deactivate proteins.
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Phospholipase C is an enzyme that cleaves PIP2 (phosphatidylinositol 4,5-bisphosphate), a phospholipid located in the plasma membrane. The products of this reaction are IP3 (inositol triphosphate) and DAG (diacylglycerol).
- IP3 acts as a second messenger by releasing Ca2+ from intracellular stores in the endoplasmic reticulum.
- DAG activates protein kinase C (PKC).
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The first messenger in the pathway involving phospholipase C is the hormone that binds to the receptor. The second messenger is IP3. Li+ inhibits phospholipase C, blocking the production of IP3 and DAG. This will disrupt the signaling pathway by preventing the release of Ca2+ from the ER and the activation of PKC.
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Two possible ways to deactivate a receptor during the termination process:
- Receptor inactivation: The receptor can become inactivated by a conformational change that reduces its affinity for the ligand.
- Receptor removal from the cell surface: The receptor can be internalized by endocytosis and degraded or recycled back to the cell surface.
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Description
Explore the fascinating world of cell communication with this quiz. Learn about key concepts such as quorum sensing, endocrine and neuroendocrine signaling, chemical synaptic signaling, and gap junctions. Test your knowledge on how cells coordinate their behavior and interact with one another.
