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Chapter 16: Problem 16

It seems counterintuitive that a cell, having a perfectly abundant supply of nutrients available, would commit suicide if not constantly stimulated by signals from other cells (see Figure \(16-6\) ). What do you suppose might be the advantages of such regulation?

Short Answer

Expert verified
Apoptosis, even with abundant nutrients, removes harmful or dysfunctional cells, thereby maintaining tissue health and efficient resource management.

Step by step solution

01

Understanding Cell Suicide

Cell suicide, or apoptosis, is a process where cells actively play a role in their own death. In the context of a cell with abundant nutrients, this process might initially seem unnecessary. However, this mechanism is crucial in maintaining the health and balance of multicellular organisms.
02

Considering the Dependency on Signals

Cells rely on signals from other cells to continue functioning normally. These signals help in communication and maintaining the correct balance of cell proliferation and death within tissues. When cells do not receive the necessary signals, they undergo apoptosis, indicating that the survival and function of cells are dependent on external cues.
03

Advantages of Regulation

The regulation ensures that only cells that are properly integrated into the organizational structure receive survival signals. This helps in removing potentially harmful cells that may become cancerous or dysfunctional. It also allows the system to efficiently manage resources and adapt to changes in the environment or developmental needs.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Cell Signaling
Cell signaling is an essential process that allows cells to communicate with each other, both near and far. This communication is vital for maintaining the organization and function of a multicellular organism.
The process of cell signaling involves:
  • Signal Reception: Cells have specific receptors on their surfaces or inside them that can detect signaling molecules distributed by other cells.
  • Signal Transduction: Once the receptor interacts with a signal, it undergoes a conformational change. This change often triggers a cascade of molecular interactions inside the cell, eventually leading to a specific response.
  • Cellular Response: The outcome of the signaling cascade might be the alteration of gene expression, triggering cell movement, changing the metabolic pathway, or even impacting cell death or survival decisions.
Through these steps, cells can adequately respond to internal or external cues, ensuring precise control of their functions and behaviors.
Exploring Cell Communication
In multicellular organisms, cell communication serves as the cornerstone for coordinating a vast array of physical and developmental processes. Effective cell communication ensures that every cell type, tissue, and organ works harmoniously.
This is mostly carried out through:
  • Direct Contact: Via structures like gap junctions in animal cells and plasmodesmata in plant cells, which allow direct passage of signaling molecules between neighboring cells.
  • Paracrine Signaling: This involves the production of signaling molecules that affect only neighboring cells, allowing for localized communication.
  • Endocrine Signaling: Hormones released into the bloodstream impact far-off cells, enabling communication over large distances within the organism.
Communication pathways ensure cells coordinate responses, maintain homeostasis, and adjust their activities based on the needs and challenges presented by the organism's environment.
The Role of Signals in Maintaining Multicellular Organisms
Multicellular organisms are complex systems composed of numerous interconnected cells that rely on communication and signaling to thrive.
Here's how signaling fits into the bigger picture:
  • Cell Survival and Proliferation: Many cells require constant input from signals to survive and divide. This "nurturing" via signals ensures that only healthy, well-functioning cells continue to exist.
  • Programmed Cell Death: Signals can instruct a cell to undergo apoptosis if they are unnecessary, damaged, or potentially dangerous. This ensures the integrity and health of the organism.
  • Developmental and Adaptive Changes: During development or when adapting to environmental shifts, signaling pathways adjust cell functions and organ structures to optimize organismal performance.
Through these signaling dynamics, multicellular organisms maintain their intricate architectures and functionality, enabling adaptation and survival.

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Most popular questions from this chapter

Two protein kinases, \(\mathrm{K} 1\) and \(\mathrm{K} 2\), function in an intracellular signaling pathway. If either kinase contains a mutation that permanently inactivates its function, no response is seen in cells when an extracellular signal is received. A different mutation in \(\mathrm{K} 1\) makes it permanently active, so that in cells containing that mutation, a response is observed even in the absence of an extracellular signal. You characterize a double-mutant cell that contains \(\mathrm{K} 2\) with the inactivating mutation and \(\mathrm{K} 1\) with the activating mutation. You observe that the response is seen even in the absence of an extracellular signal. In the normal signaling pathway, does \(\mathrm{K} 1\) activate \(\mathrm{K} 2\) or does \(\mathrm{K} 2\) activate \(\mathrm{K} 1 ?\) Explain your answer.

The Ras protein functions as a molecular switch that is set to its "on" state by other proteins that cause it to release its bound GDP and bind GTP. A GTPase-activating protein helps reset the switch to the "off" state by inducing Ras to hydrolyze its bound GTP to GDP much more rapidly than it would without this encouragement. Thus, Ras works like a light switch that one person turns on and another turns off. You are studying a mutant cell that lacks the GTPase-activating protein. What abnormalities would you expect to find in the way in which Ras activity responds to extracellular signals?

What are the similarities and differences between the reactions that lead to the activation of G proteins and the reactions that lead to the activation of Ras?

Why do you suppose cells have evolved intracellular \(\mathrm{Ca}^{2+}\) stores for signaling even though there is abundant extracellular \(\mathrm{Ca}^{2+}\) ?

Which of the following statements are correct? Explain your answers. A. The extracellular signal molecule acetylcholine has different effects on different cell types in an animal and often binds to different cell-surface receptor molecules on different cell types. B. After acetylcholine is secreted from cells, it is long-lived, because it has to reach target cells all over the body. C. Both the GTP-bound \(\alpha\) subunits and nucleotide-free \(\beta \gamma\) complexes \(-\) but not GDP-bound, fully assembled G proteins-can activate other molecules downstream of GPCRs. D. \(\mathrm{IP}_{3}\) is produced directly by cleavage of an inositol phospholipid without incorporation of an additional phosphate group. E. Calmodulin regulates the intracellular \(\mathrm{Ca}^{2+}\) concentration. F. Different signals originating from the plasma membrane can be integrated by cross-talk between different signaling pathways inside the cell. G. Tyrosine phosphorylation serves to build binding sites for other proteins to bind to RTKs.
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