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Chapter 9: Problem 39

In autoimmune lymphoproliferative syndrome (ALPS), lymphocytes which multiplied during an infection persist in the body and damage tissue. The syndrome is caused by a mutation in the F A S gene which encodes a cell surface receptor. Which signaling pathway does the receptor initiate? a. activated metabolism b. apoptosis c. cell division d. cell differentiation

Short Answer

Expert verified
b. apoptosis

Step by step solution

01

- Understand the function of the FAS receptor

The FAS receptor (also known as CD95) is a cell surface receptor that plays a crucial role in regulating programmed cell death (apoptosis). When this receptor is activated, it typically initiates a signaling cascade that leads to cell death, ensuring the elimination of potentially harmful or unnecessary cells.
02

- Clarify the options

Review the given options: activated metabolism, apoptosis, cell division, and cell differentiation. We need to identify which pathway the FAS receptor activates.
03

- Match the function to the pathway

Given that the FAS receptor's primary function is to induce programmed cell death, the correct pathway it initiates must be related to cell elimination. This matches the definition of apoptosis.
04

- Verify your answer

By comparing the receptor's function to the provided options, confirm that apoptosis is the correct signaling pathway initiated by the FAS receptor. The other options (metabolism, cell division, and cell differentiation) do not align with the function of inducing cell death.

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Key Concepts

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

FAS gene and its Role in ALPS
The **FAS gene**, also known as **TNFRSF6**, encodes the **FAS receptor (CD95)**. This gene is pivotal in regulating **programmed cell death**, or **apoptosis**. In autoimmune lymphoproliferative syndrome (ALPS), mutations in the FAS gene disrupt this regulation.
The FAS receptor is expressed on the surface of various cells. When it binds to its corresponding ligand (FasL), it triggers a cascade of events leading to cell death.

This process helps control cell growth and eliminates potentially harmful cells. In ALPS, a defective FAS gene means the receptor might not function correctly, leading to the survival of excessive lymphocytes.
  • **ALPS and Tissue Damage**: In ALPS, the inability to undergo apoptosis can cause lymphocytes to accumulate, leading to tissue damage.
  • **Genetic Mutation**: Mutations in the FAS gene impair its ability to activate apoptosis, underlining the importance of this gene in immune regulation.
Apoptosis and its Significance
**Apoptosis** is a form of programmed cell death crucial for maintaining balance within the body. Unlike necrosis, which is uncontrolled cell death, apoptosis is a regulated process that allows cells to die in a controlled manner.[...]

**Mechanism of Apoptosis**: When the FAS receptor on a cell's surface binds to the FasL, it oligomerizes and forms a **DISC** (death-inducing signaling complex). This complex activates caspases, a family of enzymes that break down the cell.
  • **Maintenance of Cell Population**: Apoptosis eliminates unnecessary or potentially harmful cells, ensuring tissues do not become overcrowded.
  • **Immune Response**: Apoptosis helps in the removal of cells that are infected or have damaged DNA, maintaining immune system integrity.
  • **Development and Aging**: This process is essential during development (e.g., removing webbing in embryos) and in the aging of cells.
Cell Surface Receptor: FAS Receptor
**Cell surface receptors** are proteins located on the cell membrane that receive and transmit signals from the external environment to the inside of the cell.
The **FAS receptor** is a type of cell surface receptor that is integral in mediating the apoptosis pathway.

Characteristic features of cell surface receptors include:
  • **Signal Receiving**: They bind to specific ligands, triggering intracellular signaling pathways.
  • **Transmembrane Proteins**: They typically span the cell membrane, with an external part binding the ligand and an internal part transmitting the signal.
  • **Specificity and Regulation**: Each receptor is specific to its ligand, and its activity can be tightly regulated to ensure appropriate cellular responses.

    **FAS Receptor Function**: When the FAS receptor binds to its ligand (FasL), it initiates a death signal that leads to apoptosis. This regulation ensures that cells with mutations or that are no longer needed are removed systematically, preventing potential damage.

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Most popular questions from this chapter

The same second messengers are used in many different cells, but the response to second messengers is different in each cell. How is this possible? a. Different cells produce the same receptor, which bind to the same ligands, but have a different response in each cell type. b. Cells produce variants of a particular receptor for a particular ligand through alternative splicing, resulting in different response in each cell c. Cells contain different genes, which produce different receptors that bind to same ligand, activating different responses in each cell. d. Cells produce different receptors that bind to the same ligand or the same receptor that binds to the same ligand with different signaling components, activating different responses in each cell.

Upon ingestion of bacteria, white blood cells release a chemical messenger into the blood stream that causes the synthesis of inflammation response proteins by liver cells. What is this is an example of? a. auto crine signaling b. endocrine signaling c. para crine signaling d. synaptic signaling

Aldosterone is a steroid hormone that regulates reabsorption of sodium ions in the kidney tubular cells. What is the probable mechanism of action of aldosterone? a. It binds gated ion channels and causes a flow of ions in the cell. b. It binds cell surface receptors and activates synthesis of cAMP. c. It binds to cell surface receptors and activates a phosphorylation cascade. d. It binds to an intra cellular receptor and activates gene transcription.

The hormone insulin binds to a receptor tyrosine kinase on the surface of target cells. Which of the following steps takes place before phosphorylation of tyrosine residues? a. A tyrosine kinase enzyme must be activated. b. GDP is exchanged for GTP. c. The receptor forms a dimer. d. The insulin molecule is internalized in the cytoplasm.

The R A S protein is a G-protein connected with the response to RTKs that initiates the M A P K kinase cascade when GDP is released and G T P uploaded. Mutations in the R A S protein which interfere with its GTPase activity are common in cancer. Evaluate the connection between the inability of R A S to hydrolyze G T P and uncontrolled cell proliferation. a. R A S, when bound to G T P, becomes permanently inactive even in the presence of the ligand, and no longer regulates cell division. b. R A S, when bound to G T P, becomes permanently active even in the absence of the ligand, and no longer regulates cell division. c. R A S, when bound to G T P, forms a dimer after binding to the ligand, and causes uncontrolled division, but it remains inactive when the ligand is absent. d. R A S, when bound to G T P, does not form a dimer after binding to the ligand but stimulates downstream signaling to occur and causes uncontrolled cell division.
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