Cell Signaling Overview and Types
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Questions and Answers

What is the primary function of glucagon in relation to blood glucose levels?

  • Inhibits glycogen breakdown
  • Decreases gluconeogenesis
  • Stimulates insulin secretion
  • Increases blood glucose levels (correct)

What stimulates the secretion of glucagon?

  • Increased insulin levels
  • Decreased catecholamine levels
  • Elevated blood glucose
  • High levels of amino acids (correct)

Which of the following statements regarding insulin action is correct?

  • Changes in enzymatic activity take seconds
  • Increased glucose uptake occurs in minutes (correct)
  • Increased glucose uptake occurs over hours
  • Changes in the amount of enzymes occur in hours to minutes

What is one effect of glucagon on lipid metabolism?

<p>Phosphorylates Acetyl CoA carboxylase (A)</p> Signup and view all the answers

Which of the following hormones is considered a counterregulatory hormone to insulin?

<p>Epinephrine (D)</p> Signup and view all the answers

What effect does glucagon have on amino acid metabolism in the liver?

<p>Promotes gluconeogenesis using amino acid C-skeletons (D)</p> Signup and view all the answers

Which step does glucagon activate first in its mechanism of action?

<p>Activation of adenylyl cyclase in the plasma membrane (C)</p> Signup and view all the answers

Which of the following correctly describes the release of insulin?

<p>It has a half-life of approximately 60 minutes. (C)</p> Signup and view all the answers

How does glucagon transduce its signal in target cells?

<p>Through a G protein-coupled receptor (D)</p> Signup and view all the answers

What is NOT a response associated with glucagon action?

<p>Activation of glycolysis in liver cells (B)</p> Signup and view all the answers

What type of molecule serves as a chemical messenger in cellular signaling?

<p>Hormones (D)</p> Signup and view all the answers

Which hormones are released in a coordinated manner to regulate blood sugar levels?

<p>Insulin and Glucagon (C)</p> Signup and view all the answers

What initiates the signaling cascade upon insulin binding to its receptor?

<p>Autophosphorylation of the receptor (B)</p> Signup and view all the answers

What is the primary metabolic effect of insulin on nutrient storage?

<p>Stimulates the conversion of glucose to TAG (C)</p> Signup and view all the answers

Which factor inhibits the secretion of insulin?

<p>Periods of physiological stress (C)</p> Signup and view all the answers

How does insulin influence glucose transport in muscle and adipose tissues?

<p>It promotes the movement of GLUT-4 to the cell membrane. (A)</p> Signup and view all the answers

What role does glucagon play in the metabolic balance of nutrients?

<p>Promotes the mobilization of stored nutrients (D)</p> Signup and view all the answers

What is the approximate half-life of insulin in plasma?

<p>6 minutes (A)</p> Signup and view all the answers

Flashcards

Insulin's Speed

Insulin's effects happen at different speeds. Glucose uptake is quick (seconds), enzyme activity changes take minutes to hours, and enzyme amounts change over hours to days.

Glucagon: What is it?

Glucagon is a peptide hormone made in the pancreas. It helps raise blood sugar when it's low.

Glucagon: Where's it made?

Glucagon is produced by alpha cells in the islets of Langerhans, which are small groups of cells found in the pancreas.

Glucagon's Job

Glucagon breaks down stored glycogen in the liver, increasing blood sugar levels. It also helps create new glucose from other sources.

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What Stimulates Glucagon?

Low blood sugar, amino acids, and catecholamines (like adrenaline) trigger glucagon release.

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Glucagon's Effect on Amino Acids

Glucagon increases the liver's uptake of amino acids released from muscles, providing carbon skeletons for gluconeogenesis.

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Glucagon's Mechanism of Action

Glucagon binds to a G protein-coupled receptor on hepatocytes, activating adenylyl cyclase and increasing cAMP levels. This activates protein kinase A, which phosphorylates key regulatory enzymes involved in CHO and lipid metabolism.

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Insulin's Release

Insulin release is stimulated by glucose.

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Glucagon Release Stimuli

Glucagon release is stimulated by low blood glucose levels and GI peptide hormones.

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Glucagon's Signaling Pathway

Glucagon signals through a G protein-coupled receptor (GPCR), leading to an increase in cAMP levels.

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What are chemical messengers?

Chemical messengers are substances produced by cells in response to specific stimuli. They travel to target cells, bind to specific receptors, and trigger a response. Their primary function is to transmit messages between cells.

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What is the role of insulin?

Insulin is a peptide hormone produced by the pancreas that helps regulate blood sugar levels. It promotes the storage of nutrients (glucose, fatty acids, and amino acids) and inhibits their release from storage.

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How does insulin secretion get regulated?

Insulin secretion is controlled by several factors. It is stimulated by increased glucose, amino acids, and gastrointestinal hormones. Secretion is inhibited during periods of stress or when dietary fuels are scarce.

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How does insulin promote storage of nutrients?

Insulin promotes the storage of nutrients as glycogen (in the liver and muscles), triglycerides (in adipose tissue), and protein (in various tissues).

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How does insulin inhibit the mobilization of stored nutrients?

Insulin prevents the breakdown of stored glycogen (to release glucose), triglycerides (to release fatty acids), and protein (to release amino acids).

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What is the insulin receptor?

The insulin receptor is a tyrosine-kinase receptor found on the surface of cells. It binds to insulin, triggering a cascade of signaling events within the cell.

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Explain signal transduction in insulin signaling.

Signal transduction involves a series of biochemical events that occur inside the cell after insulin binds to its receptor. This chain reaction starts with autophosphorylation of the receptor, leading to a cascade of responses. Dephosphorylation eventually terminates the cascade.

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What is GLUT-4 and how does insulin affect it?

GLUT-4 is a type of glucose transporter found in muscle and adipose tissue. Insulin stimulates the movement of GLUT-4 to the cell membrane, allowing more glucose to enter the cells.

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Study Notes

Cell Signaling Overview

  • Cells communicate via chemical messengers
  • These messengers are secreted in response to specific stimuli
  • They travel to target cells and bind to specific receptors
  • This binding elicits a response in the target cell
  • The function of these messengers is to transmit messages between cells

Types of Cell Signaling

  • Contact-dependent: Signaling cell and target cell are in direct contact via membrane-bound signal molecules
  • Paracrine: Signaling cell releases local mediators that diffuse to target cells in close proximity
  • Synaptic: Signaling cell (neuron) releases neurotransmitters across a synapse to a target cell
  • Endocrine: Endocrine cells release hormones into the bloodstream that travel to target cells throughout the body

Cellular Response to Signals

  • Cells can respond in diverse ways, depending on the specific signal and the target cell
  • Examples of responses include: survival, growth and division, differentiation
  • Also apoptosis (cell death)

Mechanism of Cell Signaling

  • Fast signaling pathway (seconds to minutes): Extracellular signal molecule binds to cell-surface receptor, triggers changes in existing proteins, alters cell behavior quickly
  • Slow signaling pathway (minutes to hours): Extracellular signal molecule binds to intracellular receptor, changes in protein synthesis, alters cell behavior more slowly

Chemical Messengers

  • Any substance in an organism that is secreted from a cell in response to a specific stimulus
  • Travels to a target cell and binds to a specific receptor in the target cell
  • Elicits a response
  • Function: Transmission of messages between cells

Types of Receptors

  • Cell-surface receptors: Located on the cell membrane and bind to hydrophilic signal molecules
  • Intracellular receptors: Located inside the cell and bind to small, hydrophobic signal molecules

Metabolic Effects of Insulin

  • Production: Produced by beta cells in the islets of Langerhans in the pancreas
  • Structure: Peptide hormone, half-life approximately 6 minutes
  • Stimulated by: Glucose, amino acids, gastrointestinal peptide hormones
  • Inhibited by: Conditions lacking dietary fuels, periods of physiological stress
  • Effects: Promotes storage of nutrients (glycogen, TAG, protein); inhibits mobilization of stored nutrients

Mechanism of Insulin Action

  • Binds to tyrosine kinase receptor
  • Auto-phosphorylation initiates signaling cascade
  • Promotes movement of GLUT-4 glucose transporters to cell membrane
  • Increased glucose uptake, enzymatic activity changes over time
  • Receptor regulation: internalization and degradation

Metabolic Effects of Glucagon

  • Production: Produced by alpha cells in the islets of Langerhans in the pancreas
  • Structure: Peptide hormone, short half-life
  • Stimulated by: Low blood glucose, amino acids, catecholamines
  • Inhibited by: High blood glucose, insulin
  • Effects: Promotes glycogenolysis, gluconeogenesis, ketogenesis; inhibits lipid synthesis; increases amino acid uptake by the liver

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Description

Explore the intricate world of cell signaling in this quiz. Understand the various types of signaling mechanisms, including contact-dependent, paracrine, synaptic, and endocrine. Discover how cells communicate and respond to stimuli through chemical messengers.

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