Signal Transduction and GPCRs Overview
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Questions and Answers

What is the definition of signal transduction?

The process of converting information into a chemical change.

What are the five general features of signal transduction?

Specificity, sensitivity, amplification, integration, and localization.

What are two examples of second messengers?

cAMP and Ca2+

What is the role of scaffold proteins in signal transduction?

<p>Non-enzymatic proteins that assemble interacting enzymes.</p> Signup and view all the answers

Which of the following is NOT a type of cellular signal?

<p>Gravity (B)</p> Signup and view all the answers

What are the four basic components of signal transduction?

<p>Plasma membrane receptors, G proteins, effector enzymes, and protein kinases/phosphatases.</p> Signup and view all the answers

GPCRs are the largest family of plasma membrane receptors.

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

In GPCR signaling, what activates the effector enzyme?

<p>G protein</p> Signup and view all the answers

What is the function of phosphodiesterase in the β-adrenergic receptor system?

<p>Hydrolyzes cAMP to 5’-AMP.</p> Signup and view all the answers

What is the role of CREB in signal transduction?

<p>Transcription factor phosphorylated by PKA to regulate gene expression.</p> Signup and view all the answers

What are the two products of PIP2 cleavage by phospholipase C?

<p>Diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3).</p> Signup and view all the answers

Which of the following is NOT a defect in signal transduction that can lead to disease?

<p>Increased levels of ATP (A)</p> Signup and view all the answers

Desensitization is a mechanism that allows cells to become unresponsive to persistent signals.

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

What is a key function of adaptor proteins?

<p>They confine signaling molecules to specific regions.</p> Signup and view all the answers

GPCRs activate their downstream targets directly by binding to ion channels.

<p>False (B)</p> Signup and view all the answers

What are two examples of receptor tyrosine kinases?

<p>Insulin receptor and epidermal growth factor receptor.</p> Signup and view all the answers

What are the four types of signal transducers?

<p>GPCRs, receptor tyrosine kinases, ligand-gated ion channels, and intracellular receptors.</p> Signup and view all the answers

What is the main function of ion channels?

<p>Regulate the flux of ions across cell membranes.</p> Signup and view all the answers

What is the definition of an autotroph?

<p>An organism that uses atmospheric CO2 as its sole carbon source.</p> Signup and view all the answers

Catabolism is the breakdown of molecules that releases energy.

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

Anabolism is the synthesis of molecules that requires energy.

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

What is the first law of thermodynamics?

<p>Energy is conserved.</p> Signup and view all the answers

What is the second law of thermodynamics?

<p>Systems naturally progress toward increased disorder (entropy).</p> Signup and view all the answers

What is the definition of free energy?

<p>Energy available for work.</p> Signup and view all the answers

What is the definition of enthalpy?

<p>Heat content.</p> Signup and view all the answers

Cells are considered open systems, meaning they can exchange energy and matter with their surroundings.

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

An unfavorable reaction (∆G>0) can occur when paired with a highly favorable reaction.

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

What are the four common reaction types found in metabolic reactions?

<p>Making/breaking carbon-carbon bonds, internal rearrangements, group transfer reactions, and oxidation-reduction reactions.</p> Signup and view all the answers

What is the primary role of ATP in cellular metabolism?

<p>Links energy release from catabolism to energy requirements of anabolism.</p> Signup and view all the answers

The hydrolysis of ATP releases energy due to a decrease in electrostatic repulsion.

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

What are two examples of high-energy compounds besides ATP?

<p>Phosphoenolpyruvate and 1,3-bisphosphoglycerate.</p> Signup and view all the answers

Thioesters provide higher free-energy differences compared to oxygen esters.

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

What are three key roles of ATP in metabolism?

<p>Energy provider, driving muscle contraction and biosynthesis, and transphosphorylation.</p> Signup and view all the answers

What is the purpose of electron flow in oxidation-reduction reactions?

<p>Drives all biological work.</p> Signup and view all the answers

What are two examples of electron carriers?

<p>NAD and FAD.</p> Signup and view all the answers

Niacin deficiency leads to a condition called pellagra, which is characterized by dermatitis, diarrhea, and dementia.

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

The hydrolysis of ATP can be coupled to anabolic reactions to overcome unfavorable ∆G° values.

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

What is the role of flavin nucleotides (FMN and FAD) in metabolism?

<p>Mediate oxidation-reduction reactions as tightly bound cofactors.</p> Signup and view all the answers

What are the three major pathways of glucose utilization?

<p>Glycolysis, gluconeogenesis, and the pentose phosphate pathway.</p> Signup and view all the answers

What is the definition of glycolysis?

<p>A 10-step metabolic pathway that breaks down glucose into two molecules of pyruvate.</p> Signup and view all the answers

What are the two phases of glycolysis?

<p>Preparatory phase and payoff phase.</p> Signup and view all the answers

What is the key regulatory step in glycolysis?

<p>Phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate catalyzed by phosphofructokinase-1.</p> Signup and view all the answers

Glycolysis is a reversible process in cellular metabolism.

<p>False (B)</p> Signup and view all the answers

What is the definition of gluconeogenesis?

<p>The synthesis of glucose from non-carbohydrate precursors like pyruvate, lactate, and glycerol.</p> Signup and view all the answers

Where does gluconeogenesis primarily occur?

<p>In the liver and kidney.</p> Signup and view all the answers

Gluconeogenesis and glycolysis share seven reversible reactions.

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

What are the two key enzymes involved in the conversion of pyruvate to phosphoenolpyruvate in gluconeogenesis?

<p>Pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK).</p> Signup and view all the answers

What is the definition of the Warburg effect?

<p>Tumor cells exhibit high rates of glycolysis with fermentation to lactate, even in the presence of oxygen.</p> Signup and view all the answers

What is the main function of the citric acid cycle?

<p>Oxidizes acetyl-CoA to CO2, generating high-energy electron carriers and ATP.</p> Signup and view all the answers

What is the location of the citric acid cycle within a eukaryotic cell?

<p>Mitochondrial matrix.</p> Signup and view all the answers

How much energy is conserved per molecule of acetyl-CoA that enters the citric acid cycle?

<p>3 NADH, 1 FADH2, and 1 GTP/ATP.</p> Signup and view all the answers

What is the role of the pyruvate dehydrogenase (PDH) complex?

<p>Converts pyruvate into acetyl-CoA and CO2 via oxidative decarboxylation.</p> Signup and view all the answers

The citric acid cycle is regulated by allosteric and covalent mechanisms.

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

What are three key regulatory enzymes in the citric acid cycle?

<p>Citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase.</p> Signup and view all the answers

What are the two main types of lipids?

<p>Storage lipids and structural lipids.</p> Signup and view all the answers

What is the definition of a fatty acid?

<p>Hydrocarbon derivatives with a carboxylic acid group, used for energy storage.</p> Signup and view all the answers

What are two key characteristics of fatty acids that make them good energy storage molecules?

<p>They are highly reduced and hydrophobic.</p> Signup and view all the answers

What is the difference between saturated and unsaturated fatty acids?

<p>Saturated fatty acids have no double bonds, while unsaturated fatty acids have one or more double bonds.</p> Signup and view all the answers

What are the three main components of a triacylglycerol molecule?

<p>Glycerol and three fatty acid molecules.</p> Signup and view all the answers

What are two main functions of triacylglycerols?

<p>Energy storage and insulation.</p> Signup and view all the answers

What is the basic process of partial hydrogenation?

<p>It converts cis double bonds to trans or single bonds, which increases shelf life and raises the melting point of fats.</p> Signup and view all the answers

Trans fats have been linked to several health risks, including raising LDL cholesterol levels, lowering HDL cholesterol levels, and increasing inflammatory responses.

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

What are waxes?

<p>Esters of long-chain fatty acids with long-chain alcohols.</p> Signup and view all the answers

What are the four major types of membrane lipids?

<p>Phospholipids, glycolipids, archaeal tetraether lipids, and sterols.</p> Signup and view all the answers

What is the definition of a phospholipid?

<p>A lipid with a hydrophobic tail (fatty acids) and a hydrophilic head group.</p> Signup and view all the answers

What is the main function of sterols?

<p>Maintain membrane fluidity and serve as precursors for hormones and bile acids.</p> Signup and view all the answers

What are the three primary functions of lipids in cells?

<p>Energy storage, structural role, signaling (B)</p> Signup and view all the answers

Fatty acid catabolism is the central pathway for energy production in many tissues, especially the heart and liver.

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

What is the process by which fatty acids are oxidized to acetyl-CoA?

<p>Beta-oxidation.</p> Signup and view all the answers

What are the four steps of beta-oxidation?

<p>Dehydrogenation, hydration, dehydrogenation, and thiolysis.</p> Signup and view all the answers

What are the main products of beta-oxidation?

<p>NADH, FADH2, and acetyl-CoA.</p> Signup and view all the answers

The oxidation of unsaturated fatty acids requires additional enzymes compared to the oxidation of saturated fatty acids.

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

What is the role of the carnitine shuttle?

<p>Transports long-chain fatty acids into mitochondria for beta-oxidation.</p> Signup and view all the answers

What is the main regulatory enzyme in fatty acid oxidation?

<p>Carnitine acyltransferase 1 (CAT1).</p> Signup and view all the answers

Malonyl-CoA inhibits the carnitine shuttle, preventing the simultaneous synthesis and breakdown of fatty acids.

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

What are three key takeaways regarding fatty acid catabolism?

<p>It is a central pathway for energy in many tissues, especially the heart and liver, it generates acetyl-CoA via beta-oxidation, which fuels the citric acid cycle for ATP production, and the process proceeds in distinct stages.</p> Signup and view all the answers

Flashcards

Signal Transduction Definition

The process of converting an information signal into a chemical change, generating a cellular response.

Specificity in Signal Transduction

The exact matching of signal and receptor molecules through non-covalent interactions.

Sensitivity in Signal Transduction

High receptor affinity for ligands (signal molecules), resulting in a very low dissociation constant (Kd).

Signal Amplification

Signal strength is increased by enzyme cascades.

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Signal Integration

Multiple signals are combined to produce a specific cellular response.

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Signal Localization

Contained responses in specific cellular structures (spots).

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Modularity in Signal Transduction

Signal transduction proteins have domains that recognize specific features in other proteins.

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Scaffold Proteins

Non-enzymatic proteins that assemble interacting enzymes, putting them in close proximity.

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Desensitization in Signal Transduction

Receptors become unresponsive to persistent signals.

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Signal Divergence

One initial signal can trigger multiple cellular responses.

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Plasma Membrane Receptors

Proteins embedded in the cell membrane that receive signals from outside the cell.

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G Protein

Molecules that bind GTP or GDP, relaying signals from receptors to effector enzymes.

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Effector Enzymes

Enzymes that produce second messengers in response to activated G proteins.

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Protein Kinases

Enzymes that add phosphate groups to other proteins, altering their activity.

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Protein Phosphatases

Enzymes that remove phosphate groups from proteins, reversing the effect of kinases.

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Agonist

A molecule that mimics the action of a natural ligand.

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Antagonist

A molecule that blocks the action of a natural ligand.

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GTPase Switch

G proteins inactivate by hydrolyzing GTP to GDP.

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cAMP

Cyclic AMP, a common second messenger.

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CREB

Transcription factor activated by PKA to regulate gene expression.

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Phospholipase C (PLC)

Enzyme that cleaves PIP2 into DAG and IP3.

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Ras Mutations

Mutations affecting Ras protein's GTPase activity can lead to uncontrolled cellular growth.

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Second Messenger Example

cAMP, Ca2+, IP3, diacylglycerol.

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Study Notes

Signal Transduction

  • Defined as the process of converting information into a chemical change, involving a signal detected by specific receptors
  • Conversion involves a chemical process for a cellular response
  • Key features include specificity (achieved by molecular complementarity), sensitivity (high receptor affinity), amplification (enzyme cascades), integration (multiple signals to unify response), and localization (confined signaling components for specific cellular structures)
  • Common features include modularity (multiple domains for recognizing features), scaffold proteins (non-enzymatic proteins assembling interacting enzymes), desensitization (receptors becoming unresponsive to persistent signals), and divergence (signals branching out for diverse responses)
  • Cellular signals can include hormones, neurotransmitters, growth factors, nutrients, odorants, light, tastants, etc.

G Protein-Coupled Receptors (GPCRs)

  • Largest family of plasma membrane receptors
  • Components include receptor with 7 transmembrane helices, a G protein (active: GTP-bound, inactive: GDP-bound), and effector enzyme or ion channel
  • Mechanism involves first messenger binding, receptor activation, G-protein activation, effector enzyme activation, and second messenger production (e.g., cAMP)

Steps in Signal Transduction

  • Signal binding to receptor
  • Receptor activation and second messenger or protein activity change
  • Cellular response
  • Signal transduction ends

Phospholipase C, IP3, and Ca2+ Signaling

  • Phospholipase C (PLC) cleaves PIP2 into DAG and IP3.
  • DAG activates protein kinase C (PKC).
  • IP3 releases Ca2+ from intracellular stores
  • Ca2+ acts as a second messenger

Mutations in G Protein (Ga)

  • Activating mutations cause consistently elevated cAMP levels (found in ~40% of adenomas).
  • Inactivating mutations lead to unresponsiveness to hormones using cAMP as a messenger.

Second Messengers

  • Diacylglycerol (DAG), IP3, and Ca2+

Receptor Tyrosine Kinases (RTKs)

  • Have an extracellular ligand-binding domain and a cytoplasmic tyrosine kinase domain
  • Insulin receptor activation involves dimerization, autophosphorylation, and activation of kinase activity
  • Signaling cascades involve IRS1 binding to phosphorylated Tyr residues, initiating pathways like MAPK cascade.
  • PI3K activation converts PIP2 to PIP3, leading to GLUT4 translocation.

Ion Channels and Electrical Signaling

  • Gated ion channels respond to ligands or voltage changes, regulating Na+, K+, Cl−, and Ca2+ flux.
  • Action potentials occur due to voltage-gated Na+ influx and K+ efflux, propagating signals along neurons.
  • Receptor channels include ionotropic receptors (directly gated ion channels) and metabotropic receptors (indirectly triggering second messenger pathways).

Common Features of GPCR Signaling

  • Seven transmembrane helices
  • Intrinsic GTPase activity
  • Cyclic nucleotides
  • Protein kinases
  • Encoded in many species (humans ~800 genes)

Receptor Tyrosine Kinases (RTKs)

  • Extracellular ligand-binding domain
  • Cytoplasmic tyrosine kinase domain
  • Insulin receptor activation: Dimer of aβ monomers; autophosphorylation of Tyr residues activates kinase activity
  • Signal cascade: IRS1 binds to phosphorylated Tyr residues, initiating pathways like the MAPK cascade
  • PI3K activation leads to PIP2 conversion to PIP3, GLUT4 translocation. and glycogen synthase activation.

Study Tip

  • Focus on common themes (specificity, amplification, integration, modularity, and termination).

Key Terms

  • Agonist: Mimics natural ligand effects.
  • Antagonist: Blocks receptor activity.
  • GTPase Switch: G proteins deactivate by hydrolyzing GTP to GDP.
  • CREB: Transcription factor phosphorylated by PKA to regulate gene expression.
  • Autophosphorylation: Self-phosphorylation of RTKs activates downstream signaling.
  • MAPK Cascade: Amplifies growth factor signals (Raf-1 → MEK → ERK).

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Description

Explore the fascinating world of signal transduction and G protein-coupled receptors (GPCRs). This quiz covers intrinsic processes like specificity, sensitivity, amplification, and the diverse types of cellular signals involved. Test your knowledge on the largest family of plasma membrane receptors and their significance in cellular communication.

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