AP Biology Flashcards: Signal Transduction Pathways

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This deck focuses on Signal Transduction Pathways, giving you a quick way to review the definitions, rules, and examples that matter most for AP Biology.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What are the three canonical stages of a cell signaling pathway?

Answer: Reception, transduction, response. These stages occur sequentially in all cell signaling pathways.

Flashcard 2: Identify the process by which a cell responds to a signal.

Answer: Signal transduction. It encompasses detection, transduction, and cellular response to signals.

Flashcard 3: Which second messenger is produced from ATP by adenylyl cyclase?

Answer: cAMP. cAMP is synthesized to activate kinases and amplify signals in GPCR pathways.

Flashcard 4: Identify the correct match: endocrine signaling uses local diffusion or bloodstream transport?

Answer: Bloodstream transport to distant targets. Hormones travel through blood to reach distant targets.

Flashcard 5: What type of receptor is involved in the activation of Ras proteins?

Answer: Receptor tyrosine kinases (RTKs). Growth factors bind RTKs, which then activate Ras signaling cascades.

Flashcard 6: What is synaptic signaling?

Answer: Neuron releases neurotransmitter across a synapse to a target cell. Enables rapid, precise communication between neurons.

Flashcard 7: What is a characteristic of lipid-soluble ligands?

Answer: They can cross cell membranes and bind to intracellular receptors. Lipophilic nature allows direct passage through cell membranes.

Flashcard 8: What is a receptor tyrosine kinase (RTK)?

Answer: A membrane receptor that dimerizes and autophosphorylates. Has intrinsic kinase activity activated by dimerization.

Flashcard 9: What is synaptic signaling?

Answer: Neuron releases neurotransmitter across synapse to a target cell. Synaptic signaling ensures rapid, precise communication between neurons and targets.

Flashcard 10: What nucleotide exchange activates a G protein after GPCR stimulation?

Answer: GDP is replaced by GTP on the G protein. GTP binding causes conformational change and activation.

Flashcard 11: What type of receptor is involved in the activation of Ras proteins?

Answer: Receptor tyrosine kinases (RTKs). Growth factors bind RTKs, which then activate Ras signaling cascades.

Flashcard 12: Describe the function of a second messenger in signal transduction.

Answer: To relay signals from receptors to target molecules inside the cell. They amplify signals and allow for rapid cellular responses.

Flashcard 13: What is signal amplification in a transduction pathway?

Answer: One ligand triggers activation of many downstream molecules. Amplification allows a single signal to generate a robust cellular response through cascading activations.

Flashcard 14: What enzyme produces cAMP from ATP in many GPCR pathways?

Answer: Adenylyl cyclase. Converts ATP to cAMP when activated by G proteins.

Flashcard 15: What is the primary kinase activated by cAMP in many pathways?

Answer: Protein kinase A (PKA). PKA phosphorylates target proteins to mediate diverse cellular responses.

Flashcard 16: What is the role of feedback inhibition in signal transduction?

Answer: To regulate and fine-tune the signaling pathway. Product inhibits earlier steps to prevent overactivation of pathways.

Flashcard 17: Which option best describes a scaffold protein in signaling?

Answer: A protein that organizes pathway components for efficient signaling. Increases specificity and speed by co-localizing components.

Flashcard 18: Which option best describes an intracellular receptor: binds hydrophobic ligand or hydrophilic ligand?

Answer: Binds hydrophobic ligand. Intracellular receptors typically interact with hydrophobic ligands that can diffuse through the plasma membrane.

Flashcard 19: Which molecule is released by IP₃ in signal transduction?

Answer: Calcium ions (Ca²⁺) from the endoplasmic reticulum. IP₃ binds to ER receptors, triggering calcium release into cytoplasm.

Flashcard 20: What is paracrine signaling?

Answer: Local signaling to nearby cells by secreted molecules. Paracrine signals diffuse locally to coordinate responses in neighboring cells.

Flashcard 21: What is a ligand in cell signaling?

Answer: A signaling molecule that binds a receptor. Acts as the signal that initiates the pathway.

Flashcard 22: What is a G protein-coupled receptor (GPCR)?

Answer: A membrane receptor that activates a G protein. Seven transmembrane helices characterize this receptor type.

Flashcard 23: Which enzyme synthesizes cAMP in response to an activated G protein?

Answer: Adenylyl cyclase. Activated G proteins stimulate adenylyl cyclase to convert ATP into cAMP.

Flashcard 24: What is the function of nitric oxide in signal transduction?

Answer: To act as a signaling molecule that diffuses across membranes. NO diffuses freely and activates guanylyl cyclase in target cells.

Flashcard 25: What is the importance of signal amplification in pathways?

Answer: To increase the strength of the signal and ensure a robust response. One signal molecule can activate many downstream effectors in cascade fashion.

Flashcard 26: What is a second messenger in signal transduction?

Answer: A small intracellular molecule that relays/amplifies a signal. Propagates signal from membrane to cytoplasm.

Flashcard 27: What does IP$_3$ primarily do in many signaling pathways?

Answer: Opens ER $Ca^{2+}$ channels to raise cytosolic $Ca^{2+}$. Binds IP$_3$ receptors on ER to release stored calcium.

Flashcard 28: What is a ligand in the context of signal transduction?

Answer: A molecule that binds to a receptor to initiate signaling. Specific binding ensures only appropriate cells respond to signals.

Flashcard 29: What is cross-talk in the context of signal transduction pathways?

Answer: Interaction between different signaling pathways. Pathways can influence each other, creating integrated cellular responses.

Flashcard 30: What enzyme family is most directly responsible for executing apoptosis?

Answer: Caspases (proteases). These proteases cleave specific proteins to dismantle cells.

Flashcard 31: Which pathway is involved in the rapid response to stress?

Answer: The adrenergic signaling pathway. Epinephrine and norepinephrine activate this fight-or-flight response.

Flashcard 32: What is signal reception in a signal transduction pathway?

Answer: Ligand binding activates a specific receptor. The first step where signal molecules bind to their target receptors.

Flashcard 33: Identify a receptor type that can directly alter gene expression.

Answer: Intracellular receptors. These receptors act as ligand-activated transcription factors.

Flashcard 34: Identify the primary messenger in a signal transduction pathway.

Answer: The signaling molecule or ligand. It's the external signal that triggers the pathway by binding to receptors.

Flashcard 35: Which protein is activated by the binding of GTP in GPCR pathways?

Answer: The G protein. GTP binding activates the G protein, enabling it to activate effectors.

Flashcard 36: What is the role of calmodulin in signal transduction?

Answer: To bind calcium ions and activate enzymes. This calcium-binding protein regulates many calcium-dependent processes.

Flashcard 37: What enzyme cleaves PIP$_2$ into DAG and IP$_3$?

Answer: Phospholipase C. Often activated by Gq proteins in GPCR pathways.

Flashcard 38: Describe the function of a second messenger in signal transduction.

Answer: To relay signals from receptors to target molecules inside the cell. They amplify signals and allow for rapid cellular responses.

Flashcard 39: What is a common second messenger released from the endoplasmic reticulum?

Answer: Calcium ions ($Ca^{2+}$). ER stores $Ca^{2+}$ until released by IP$_3$ or other signals.

Flashcard 40: What is signal transduction in a signal transduction pathway?

Answer: Intracellular relay converts signal to cellular action. Converts external signals into internal molecular changes.

Flashcard 41: Which type of signaling molecule most often uses intracellular receptors: polar or nonpolar?

Answer: Nonpolar (hydrophobic) molecules. Can cross membranes due to their lipid solubility.

Flashcard 42: What is the result of phospholipase C activation?

Answer: Production of IP₃ and DAG. PLC splits PIP₂ into these two distinct second messenger molecules.

Flashcard 43: Which type of receptor directly forms an ion channel when activated by a ligand?

Answer: Ligand-gated ion channel receptor. Ligand binding induces a conformational change that opens the channel for ion passage.

Flashcard 44: What type of protein is activated by a GPCR to relay the signal?

Answer: A G protein (GTP-binding protein). G proteins act as molecular switches activated by GPCRs to relay signals intracellularly.

Flashcard 45: What does IP$_3$ primarily do in many signaling pathways?

Answer: Opens ER $Ca^{2+}$ channels to raise cytosolic $Ca^{2+}$. Binds IP$_3$ receptors on ER to release stored calcium.

Flashcard 46: What immediate cellular change occurs when a ligand-gated ion channel opens?

Answer: Ion flow changes membrane potential or intracellular ion levels. Ion influx or efflux alters electrical or chemical gradients, influencing cellular functions.

Flashcard 47: What is apoptosis in the context of cell signaling responses?

Answer: Programmed cell death. Controlled cell suicide for development or damage response.

Flashcard 48: What is signal amplification in a transduction pathway?

Answer: One activated molecule triggers activation of many downstream molecules. Produces exponential increase in active signaling molecules.

Flashcard 49: What is a phosphorylation cascade in signal transduction?

Answer: Sequential activation of kinases by phosphorylation. Cascades amplify signals through successive phosphorylation events in kinase hierarchies.

Flashcard 50: What is the difference between a local regulator and a hormone?

Answer: Local: nearby targets; hormone: long-distance via bloodstream. Local regulators act short-range, while hormones enable systemic communication via circulation.

Flashcard 51: What is the primary function of protein kinases in signal transduction?

Answer: To phosphorylate target proteins, altering their activity. Phosphorylation changes protein shape and function, activating or inhibiting them.

Flashcard 52: What is a common second messenger released from the endoplasmic reticulum?

Answer: Calcium ions ($Ca^{2+}$). ER stores $Ca^{2+}$ until released by IP$_3$ or other signals.

Flashcard 53: What is the function of the MAP kinase pathway?

Answer: To transmit signals from the cell surface to the DNA in the nucleus. It's a three-kinase cascade that regulates gene expression.

Flashcard 54: What is the result of a ligand binding to a receptor tyrosine kinase?

Answer: Dimerization and autophosphorylation. Two receptors pair up and phosphorylate each other's tyrosine residues.

Flashcard 55: What is the role of a receptor in signal transduction?

Answer: To bind the ligand and initiate a cellular response. Receptors undergo conformational changes when bound to transmit signals.

Flashcard 56: What event turns off a G protein in a GPCR pathway?

Answer: GTP hydrolysis to GDP by the G protein. The G protein's intrinsic GTPase activity terminates signaling.

Flashcard 57: Which option best describes a negative feedback loop in cell signaling?

Answer: A downstream effect reduces the original signaling activity. Product of pathway inhibits earlier steps to prevent overactivation.

Flashcard 58: What key receptor event commonly follows ligand binding to an RTK?

Answer: Receptor dimerization. Two receptors come together to enable cross-phosphorylation.

Flashcard 59: Which type of receptor is involved in the G protein-coupled pathways?

Answer: G protein-coupled receptors (GPCRs). These seven-transmembrane proteins activate G proteins when ligand-bound.

Flashcard 60: What intracellular protein commonly binds $Ca^{2+}$ to help regulate enzymes?

Answer: Calmodulin. Changes conformation when bound to $Ca^{2+}$ to activate targets.

Flashcard 61: What is the direct biochemical action of a protein kinase on its substrate?

Answer: Phosphorylation of the substrate protein. Adds phosphate from ATP to serine, threonine, or tyrosine.

Flashcard 62: What is autophosphorylation in RTK activation?

Answer: Each receptor phosphorylates tyrosines on the other receptor. This process creates phosphotyrosine sites that recruit and activate downstream signaling proteins.

Flashcard 63: What is the effect of ligand binding on ion channel receptors?

Answer: Opening or closing of the channel. Ligand binding changes channel conformation to allow ion flow.

Flashcard 64: Which enzyme converts ATP to cAMP in signal transduction?

Answer: Adenylyl cyclase. It's activated by G proteins and catalyzes the formation of cAMP.

Flashcard 65: Identify the primary intracellular target of cAMP.

Answer: Protein kinase A (PKA). cAMP binds to and activates this key regulatory kinase.

Flashcard 66: Which enzyme degrades cAMP in signal transduction pathways?

Answer: Phosphodiesterase. It breaks down cAMP to 5'-AMP, terminating the signal.

Flashcard 67: What is the role of feedback inhibition in signal transduction?

Answer: To regulate and fine-tune the signaling pathway. Product inhibits earlier steps to prevent overactivation of pathways.

Flashcard 68: What is the role of a scaffold protein in signal transduction?

Answer: To organize and facilitate interactions between proteins. They bring signaling molecules together for efficient pathway operation.

Flashcard 69: Identify the primary intracellular target of cAMP.

Answer: Protein kinase A (PKA). cAMP binds to and activates this key regulatory kinase.

Flashcard 70: What is a receptor tyrosine kinase (RTK)?

Answer: A kinase receptor that phosphorylates tyrosines upon activation. RTKs dimerize and autophosphorylate on tyrosine residues to initiate signaling cascades.

Flashcard 71: What is the result of phospholipase C activation?

Answer: Production of IP₃ and DAG. PLC splits PIP₂ into these two distinct second messenger molecules.

Flashcard 72: What is the result of a ligand binding to a receptor tyrosine kinase?

Answer: Dimerization and autophosphorylation. Two receptors pair up and phosphorylate each other's tyrosine residues.

Flashcard 73: Identify the primary messenger in a signal transduction pathway.

Answer: The signaling molecule or ligand. It's the external signal that triggers the pathway by binding to receptors.

Flashcard 74: What is the role of calmodulin in signal transduction?

Answer: To bind calcium ions and activate enzymes. This calcium-binding protein regulates many calcium-dependent processes.

Flashcard 75: What is the result of ligand binding to a nuclear receptor?

Answer: Regulation of gene transcription. Hormone-receptor complex binds DNA and regulates gene transcription.

Flashcard 76: Identify a mechanism that ensures specificity in signal transduction.

Answer: Receptor-ligand specificity. Only matching ligand-receptor pairs trigger responses in target cells.

Flashcard 77: State the role of phosphatases in signal transduction pathways.

Answer: To remove phosphate groups from proteins. They reverse kinase action and help terminate signaling pathways.

Flashcard 78: What is a ligand in cell signaling?

Answer: A signaling molecule that binds a receptor. Acts as the signal that initiates the pathway.

Flashcard 79: What are the three canonical stages of a cell signaling pathway?

Answer: Reception, transduction, response. These stages sequentially detect an extracellular signal, convert it into intracellular messages, and elicit a cellular change.

Flashcard 80: Which enzyme terminates cAMP signaling by converting cAMP to AMP?

Answer: Phosphodiesterase. Phosphodiesterase hydrolyzes cAMP, rapidly terminating the signal to prevent prolonged activation.

Flashcard 81: What is a second messenger in signal transduction?

Answer: A small intracellular molecule that relays/amplifies a signal. Propagates signal from membrane to cytoplasm.

Flashcard 82: What enzyme produces cAMP from ATP in many GPCR pathways?

Answer: Adenylyl cyclase. Converts ATP to cAMP when activated by G proteins.

Flashcard 83: What is the primary target activated by cAMP in many animal cells?

Answer: Protein kinase A (PKA). cAMP binds PKA regulatory subunits, releasing catalytic subunits.

Flashcard 84: Identify a common effect of signal transduction in muscle cells.

Answer: Muscle contraction. Calcium release triggers actin-myosin interaction for muscle contraction.

Flashcard 85: What is the direct biochemical action of a protein kinase on its substrate?

Answer: Phosphorylation of the substrate protein. Adds phosphate from ATP to serine, threonine, or tyrosine.

Flashcard 86: What class of enzyme removes phosphate groups from proteins in signaling pathways?

Answer: Protein phosphatases. Reverse kinase actions to terminate signaling.

Flashcard 87: What is a ligand in the context of signal transduction?

Answer: A molecule that binds to a receptor to initiate signaling. Specific binding ensures only appropriate cells respond to signals.

Flashcard 88: Identify a signaling pathway that uses phospholipase C.

Answer: The phosphoinositide pathway. PLC cleaves PIP₂ to generate two important second messengers.

Flashcard 89: Which type of signaling molecule most often uses intracellular receptors: polar or nonpolar?

Answer: Nonpolar (hydrophobic) molecules. Can cross membranes due to their lipid solubility.

Flashcard 90: What is the function of nitric oxide in signal transduction?

Answer: To act as a signaling molecule that diffuses across membranes. NO diffuses freely and activates guanylyl cyclase in target cells.

Flashcard 91: Identify a common effect of signal transduction in muscle cells.

Answer: Muscle contraction. Calcium release triggers actin-myosin interaction for muscle contraction.

Flashcard 92: What is a ligand-gated ion channel receptor?

Answer: A receptor that opens/closes an ion channel when ligand binds. Allows rapid ion flow to change membrane potential.

Flashcard 93: Which molecule is released by IP₃ in signal transduction?

Answer: Calcium ions (Ca²⁺) from the endoplasmic reticulum. IP₃ binds to ER receptors, triggering calcium release into cytoplasm.

Flashcard 94: Which protein is activated by the binding of GTP in GPCR pathways?

Answer: The G protein. GTP binding activates the G protein, enabling it to activate effectors.

Flashcard 95: What is a cell-surface receptor?

Answer: A transmembrane protein that binds extracellular ligand. Cell-surface receptors span the membrane to detect hydrophilic ligands that cannot cross it.

Flashcard 96: What is the definition of a signal transduction pathway?

Answer: A series of molecular events that lead to a cellular response. It converts extracellular signals into intracellular responses through three main steps.

Flashcard 97: What is the function of GTPases like Ras in signaling pathways?

Answer: Molecular switches that cycle between GTP-bound and GDP-bound states. GTPases regulate signaling by toggling between active GTP and inactive GDP forms.

Flashcard 98: Identify the principle that explains why only certain cells respond to a given ligand.

Answer: Only target cells with the specific receptor can respond. Receptor specificity ensures targeted responses, preventing indiscriminate signaling.

Flashcard 99: Identify the correct match: paracrine signaling acts on nearby cells or distant cells?

Answer: Nearby cells. Signal diffuses locally to affect neighboring cells.

Flashcard 100: What nucleotide exchange activates the alpha subunit of a G protein?

Answer: GDP is replaced by GTP. GTP binding induces a conformational change that dissociates the alpha subunit for downstream signaling.