Chapter 8: Problem 1

Describe the six functional components of a signaling pathway that is initiated outside of the cell and culminates with activation of a metabolic enzyme. Provide specific examples of each component.

Short Answer

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In summary, the six functional components of a signaling pathway include: 1. Extracellular Signal (Ligand) - e.g., insulin 2. Cell Surface Receptor - e.g., insulin receptor 3. Intracellular Signal Transduction - e.g., insulin receptor substrates (IRS) proteins and PI3K 4. Signal Amplification and Diversification - e.g., PIP3 as a second messenger 5. Target Molecules and Effectors - e.g., Akt and mTOR 6. Termination and Signal Resetting - e.g., phosphatases, such as PP2A and PTEN These components aid in transmitting and modulating signals from the extracellular environment to the intracellular environment, ultimately affecting cellular metabolism and function.

Step by step solution

Extracellular Signal (Ligand)

The first component of a signaling pathway is the extracellular signal or ligand. This molecule is responsible for initiating the signaling cascade by binding to a receptor on the cell membrane. Example: Insulin, a hormone released by the pancreas that regulates glucose homeostasis, acts as an extracellular signal that initiates a signaling pathway in its target cells.

Cell Surface Receptor

The second component is the cell surface receptor that binds to the extracellular signal. Once the ligand binds to the receptor, it initiates a conformational change, allowing the receptor to transmit the signal into the cell. Example: Insulin binds to the insulin receptor, a transmembrane protein on the surface of target cells.

Intracellular Signal Transduction

The third component involves intracellular signal transduction, which refers to the series of events that occurs within a cell after receptor activation. This step typically involves proteins, or a series of proteins, that transmit the signal from the cell surface to the target molecule. Example: In the insulin signaling pathway, insulin receptor substrates (IRS) proteins are phosphorylated and activate phosphatidylinositol 3-kinase (PI3K), propagating the signal downstream.

Signal Amplification and Diversification

The fourth component is signal amplification and diversification. In this step, the initial signal is amplified, allowing the pathway to have a significant impact on the target enzyme and other cell components. Additionally, the signal can be split into multiple branches to affect different targets within the cell. Example: In the insulin signaling pathway, activated PI3K generates phosphatidylinositol (3,4,5)-trisphosphate (PIP3), which acts as a second messenger to amplify and diversify the signal.

Target Molecules and Effectors

The fifth component deals with the target molecules and effectors involved in the signaling pathway. These molecules, usually proteins or enzymes, exert the final effect on the metabolic activity inside the cell. Example: In the insulin signaling pathway, the target molecules and effectors include protein kinase B (PKB or Akt) and mammalian target of rapamycin (mTOR), which play essential roles in glucose uptake and protein synthesis, respectively.

Termination and Signal Resetting

The sixth and final component is the termination and signal resetting phase. This step ensures that the cell can return to its basal signaling state and be ready for future signaling events. Termination mechanisms may involve enzymes that degrade the signaling molecules or proteins that remove phosphate groups, thus inactivating the signaling proteins. Example: In the insulin signaling pathway, phosphatases such as protein phosphatase 2A (PP2A) and PTEN can remove phosphate groups from signaling proteins, helping to terminate the signal and reset the pathway.

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Describe the six functional components of a signaling pathway that is initiated outside of the cell and culminates with activation of a metabolic enzyme. Provide specific examples of each component.

Short Answer

Step by step solution

Extracellular Signal (Ligand)

Cell Surface Receptor

Intracellular Signal Transduction

Signal Amplification and Diversification

Target Molecules and Effectors

Termination and Signal Resetting

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