AP Biology Flashcards: Introduction To Signal Transduction

What this deck covers

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

How to use these flashcards

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 is the role of a protein kinase in signal transduction?

Answer: To phosphorylate proteins, altering their activity. Adds phosphate groups to activate/deactivate proteins.

Flashcard 2: What are the two second messengers produced when PIP$2$ is cleaved?

Answer: IP$3$ and DAG. Two different second messengers produced from one membrane lipid.

Flashcard 3: What is the result of signal amplification in a pathway?

Answer: A small signal produces a large cellular response. Each step multiplies signal strength exponentially.

Flashcard 4: What are the three classic stages of cell signaling in order?

Answer: Reception, transduction, response. Standard pathway: detect signal, process it, then act on it.

Flashcard 5: What role do G-proteins play in signal transduction?

Answer: They transmit signals from receptors to enzymes. Act as molecular switches linking receptors to effectors.

Flashcard 6: What is a cell-surface receptor used for?

Answer: Detecting extracellular hydrophilic signals at the plasma membrane. Water-soluble signals can't cross membranes so need surface receptors.

Flashcard 7: Identify the second messenger produced by adenylyl cyclase.

Answer: cAMP. Cyclic adenosine monophosphate, a major signaling molecule in cells.

Flashcard 8: What is the significance of receptor dimerization in signal transduction?

Answer: It activates receptor tyrosine kinases. Two receptors pair to activate their kinase domains.

Flashcard 9: Identify the second messenger produced by adenylyl cyclase.

Answer: cAMP. Cyclic adenosine monophosphate, a major signaling molecule in cells.

Flashcard 10: Identify the most direct effect of a constitutively active receptor mutation.

Answer: Pathway activation occurs even without ligand binding. Always-active receptor signals continuously regardless of ligand presence.

Flashcard 11: Identify the term for long-distance signaling via hormones in the bloodstream.

Answer: Endocrine signaling. Hormones travel through circulation to reach distant target cells.

Flashcard 12: What is the result of signal amplification in a pathway?

Answer: A small signal produces a large cellular response. Each step multiplies signal strength exponentially.

Flashcard 13: What is a receptor in cell signaling?

Answer: A protein that binds a ligand and initiates signal transduction. Detects specific ligands and starts the signaling cascade inside cells.

Flashcard 14: Which property of a ligand usually determines whether it crosses the membrane unaided?

Answer: Hydrophobic (nonpolar) ligands cross; hydrophilic ligands do not. Polar molecules can't cross lipid membranes without transport proteins.

Flashcard 15: Define 'second messenger' in the context of signal transduction.

Answer: Small molecules that relay signals inside the cell. Intracellular messengers that amplify receptor signals.

Flashcard 16: Identify the term for one signaling molecule affecting nearby cells.

Answer: Paracrine signaling. Local signaling between cells in the same tissue area.

Flashcard 17: What is the primary role of DAG in many signaling pathways?

Answer: It helps activate protein kinase C (PKC) at the membrane. Lipid second messenger that works with calcium to activate PKC.

Flashcard 18: Which molecule is a key component of the IP3/DAG pathway?

Answer: Inositol triphosphate (IP3). Second messenger that triggers calcium release from ER.

Flashcard 19: What is signal transduction in cell communication?

Answer: Conversion of an external signal into a specific cellular response. Cells detect external signals and produce specific internal responses.

Flashcard 20: Identify the most direct effect of a loss-of-function mutation in a receptor protein.

Answer: Reduced or absent cellular response to that ligand. Non-functional receptor cannot detect or respond to its ligand.

Flashcard 21: Identify the membrane phospholipid that is cleaved to form IP$3$ and DAG.

Answer: PIP$2$ (phosphatidylinositol 4,5-bisphosphate). Membrane lipid substrate that gets cleaved by phospholipase C enzyme.

Flashcard 22: Which type of response is typically faster: altering enzyme activity or altering gene expression?

Answer: Altering enzyme activity is typically faster. Protein modification occurs immediately; gene expression requires transcription time.

Flashcard 23: What are the three classic stages of cell signaling in order?

Answer: Reception, transduction, response. Standard pathway: detect signal, process it, then act on it.

Flashcard 24: What is the role of protein phosphatases in signal transduction?

Answer: They remove phosphate groups from proteins to regulate signaling. Dephosphorylation reverses kinase effects to terminate or modulate signaling.

Flashcard 25: What is the role of protein kinases in signal transduction?

Answer: They transfer phosphate groups to target proteins to alter activity. Phosphorylation changes protein shape and function to propagate signals.

Flashcard 26: Identify the primary protein kinase activated by cAMP in many pathways.

Answer: Protein kinase A (PKA). cAMP-dependent enzyme that phosphorylates target proteins for cellular responses.

Flashcard 27: What is a ligand in cell signaling?

Answer: A signaling molecule that binds to a receptor. The signal molecule that triggers cellular responses by receptor binding.

Flashcard 28: What nucleotide replaces GDP to activate a G protein alpha subunit?

Answer: GTP. High-energy nucleotide activates the alpha subunit for signaling.

Flashcard 29: What is the function of calmodulin in Ca$^{2+}$ signaling?

Answer: A Ca$^{2+}$-binding protein that activates target enzymes and proteins. Calcium sensor protein that changes shape when bound to calcium.

Flashcard 30: What enzyme converts ATP into cAMP in many GPCR pathways?

Answer: Adenylyl cyclase. G protein-activated enzyme that synthesizes the second messenger cAMP.

Flashcard 31: Identify a receptor type that is intracellular.

Answer: Steroid hormone receptors. Lipophilic hormones cross membrane to bind inside cell.

Flashcard 32: Identify the purpose of feedback inhibition in signal transduction.

Answer: To regulate and maintain cellular responses. Prevents excessive signaling by inhibiting pathway components.

Flashcard 33: What are the two second messengers produced when PIP$2$ is cleaved?

Answer: IP$3$ and DAG. Two different second messengers produced from one membrane lipid.

Flashcard 34: Identify the initial step in a signal transduction pathway.

Answer: Signal reception by a receptor protein. First step where signaling molecule binds to receptor.

Flashcard 35: Identify the term for signaling that requires direct cell-to-cell contact.

Answer: Juxtacrine (contact-dependent) signaling. Membrane-bound signals require physical touching between cells.

Flashcard 36: Which option best predicts the effect of inhibiting protein phosphatases in a pathway?

Answer: Phosphorylated signaling proteins persist longer, prolonging signaling. Without dephosphorylation, active phosphoproteins accumulate and maintain signaling.

Flashcard 37: Which molecules are often targets of phosphorylation in signal transduction?

Answer: Serine, threonine, and tyrosine residues. Amino acid residues modified by kinases for regulation.

Flashcard 38: What is a second messenger in cell signaling?

Answer: A small intracellular molecule that relays and amplifies a signal. Diffusible molecules that spread signals throughout the cell interior.

Flashcard 39: What is signal amplification in a transduction pathway?

Answer: A small input triggers a larger output through multi-step activation. Each step activates many molecules, creating exponential signal growth.

Flashcard 40: What nucleotide is bound to an inactive G protein alpha subunit?

Answer: GDP. Low-energy state keeps the G protein subunits together and inactive.

Flashcard 41: What is the main function of the MAP kinase pathway?

Answer: To regulate gene expression and cell division. Phosphorylation cascade controlling cell growth and differentiation.

Flashcard 42: Which molecule is commonly involved in autocrine signaling?

Answer: Growth factors. Molecules that stimulate the same cell that secreted them.

Flashcard 43: Identify the receptor class that activates a G protein upon ligand binding.

Answer: G protein-coupled receptor (GPCR). Seven transmembrane protein that activates intracellular G proteins.

Flashcard 44: Which molecules are often targets of phosphorylation in signal transduction?

Answer: Serine, threonine, and tyrosine residues. Amino acid residues modified by kinases for regulation.

Flashcard 45: What is a receptor in cell signaling?

Answer: A protein that binds a ligand and initiates signal transduction. Detects specific ligands and starts the signaling cascade inside cells.

Flashcard 46: Identify a key function of the JAK-STAT signaling pathway.

Answer: To transmit signals from cytokines to the nucleus. Cytokine-activated pathway directly phosphorylating transcription factors.

Flashcard 47: What happens during signal transduction when a ligand binds to a receptor?

Answer: The receptor undergoes a conformational change. Shape change allows receptor to interact with other proteins.

Flashcard 48: Which type of signaling involves direct contact between cells?

Answer: Juxtacrine signaling. Cell-to-cell contact signaling via membrane-bound molecules.

Flashcard 49: Describe the role of scaffolding proteins in signal transduction.

Answer: They enhance the efficiency of signal transduction. Organize signaling proteins for faster interactions.

Flashcard 50: What is the primary effect of an ion channel-linked receptor once activated?

Answer: It allows ion flow across the membrane. Ligand binding opens channel for specific ion movement.

Flashcard 51: What is autophosphorylation in an RTK?

Answer: The receptor phosphorylates its own tyrosine residues after activation. Activated receptor adds phosphates to its own tyrosine amino acids.

Flashcard 52: What is a cell-surface receptor used for?

Answer: Detecting extracellular hydrophilic signals at the plasma membrane. Water-soluble signals can't cross membranes so need surface receptors.

Flashcard 53: Which type of response is typically faster: altering enzyme activity or altering gene expression?

Answer: Altering enzyme activity is typically faster. Protein modification occurs immediately; gene expression requires transcription time.

Flashcard 54: What is the primary purpose of a signal transduction cascade?

Answer: To amplify the signal and ensure a specific response. Sequential protein interactions amplify and direct signal.

Flashcard 55: What immediate effect occurs when a ligand opens a ligand-gated ion channel?

Answer: Ion flow changes membrane potential and/or cytosolic ion levels. Changed electrical properties trigger rapid cellular responses.

Flashcard 56: Identify the receptor class that dimerizes and autophosphorylates on tyrosines.

Answer: Receptor tyrosine kinase (RTK). Ligand binding causes two receptors to pair and cross-phosphorylate.

Flashcard 57: What is the main function of a receptor tyrosine kinase?

Answer: To transfer phosphate groups to tyrosine residues. Autophosphorylation activates kinase domain for downstream signaling.

Flashcard 58: What is the role of the Ras protein in signal transduction?

Answer: To relay signals from receptor tyrosine kinases. GTPase that activates MAP kinase cascades downstream.

Flashcard 59: What is the role of the Ras protein in signal transduction?

Answer: To relay signals from receptor tyrosine kinases. GTPase that activates MAP kinase cascades downstream.

Flashcard 60: Identify the term for a cell signaling to itself by secreting a ligand it also detects.

Answer: Autocrine signaling. Self-signaling allows cells to regulate their own activity.

Flashcard 61: What is a ligand in cell signaling?

Answer: A signaling molecule that binds to a receptor. The signal molecule that triggers cellular responses by receptor binding.

Flashcard 62: What is a phosphorylation cascade?

Answer: Sequential activation of kinases via phosphorylation. Each active kinase phosphorylates multiple downstream kinases for amplification.

Flashcard 63: Name a type of receptor that is also an enzyme.

Answer: Receptor tyrosine kinases. Dual-function proteins with catalytic activity when activated.

Flashcard 64: Define 'second messenger' in the context of signal transduction.

Answer: Small molecules that relay signals inside the cell. Intracellular messengers that amplify receptor signals.

Flashcard 65: What is an intracellular receptor used for?

Answer: Binding small hydrophobic ligands inside the cell to regulate activity. Lipid-soluble molecules can enter cells and bind internal proteins.

Flashcard 66: What immediate effect occurs when a ligand opens a ligand-gated ion channel?

Answer: Ion flow changes membrane potential and/or cytosolic ion levels. Changed electrical properties trigger rapid cellular responses.

Flashcard 67: Which enzyme is activated by cAMP in many signal transduction pathways?

Answer: Protein kinase A (PKA). cAMP-activated kinase that phosphorylates target proteins.

Flashcard 68: Identify the initial step in a signal transduction pathway.

Answer: Signal reception by a receptor protein. First step where signaling molecule binds to receptor.

Flashcard 69: Identify the type of signaling where cells communicate over short distances.

Answer: Paracrine signaling. Local signaling between nearby cells via diffusion.

Flashcard 70: What is the primary function of a signal transduction pathway?

Answer: To convert an external signal into a cellular response. Converts extracellular stimuli into intracellular responses.

Flashcard 71: Identify a common second messenger in signal transduction pathways.

Answer: cAMP (cyclic adenosine monophosphate). Universal second messenger activated by adenylyl cyclase.

Flashcard 72: What is the role of adenylyl cyclase in signal transduction?

Answer: It converts ATP to cAMP. G-protein activated enzyme producing cAMP second messenger.

Flashcard 73: What is the role of adenylyl cyclase in signal transduction?

Answer: It converts ATP to cAMP. G-protein activated enzyme producing cAMP second messenger.

Flashcard 74: Identify the term for a cell signaling to itself by secreting a ligand it also detects.

Answer: Autocrine signaling. Self-signaling allows cells to regulate their own activity.

Flashcard 75: Identify a receptor type that is intracellular.

Answer: Steroid hormone receptors. Lipophilic hormones cross membrane to bind inside cell.

Flashcard 76: Which property of a ligand usually determines whether it crosses the membrane unaided?

Answer: Hydrophobic (nonpolar) ligands cross; hydrophilic ligands do not. Polar molecules can't cross lipid membranes without transport proteins.

Flashcard 77: Define 'ligand' in the context of cell signaling.

Answer: A molecule that binds specifically to a receptor. Signal molecule with specific receptor binding affinity.

Flashcard 78: What is the function of calmodulin in Ca$^{2+}$ signaling?

Answer: A Ca$^{2+}$-binding protein that activates target enzymes and proteins. Calcium sensor protein that changes shape when bound to calcium.

Flashcard 79: What ends signaling by a G protein alpha subunit?

Answer: Hydrolysis of GTP to GDP by the alpha subunit (GTPase activity). Built-in enzyme activity returns G protein to inactive state.

Flashcard 80: What is the role of diacylglycerol (DAG) in signal transduction?

Answer: It acts as a second messenger with IP3. Lipid messenger that activates protein kinase C.

Flashcard 81: Identify a key characteristic of signal transduction pathways.

Answer: Specificity and regulation of cellular responses. Ensures appropriate cellular responses to external stimuli.

Flashcard 82: Describe the role of scaffolding proteins in signal transduction.

Answer: They enhance the efficiency of signal transduction. Organize signaling proteins for faster interactions.

Flashcard 83: Identify the main receptor class that forms an ion channel when activated.

Answer: Ligand-gated ion channel receptor. Opens ion channels directly when ligand binds to receptor.

Flashcard 84: What is the primary role of DAG in many signaling pathways?

Answer: It helps activate protein kinase C (PKC) at the membrane. Lipid second messenger that works with calcium to activate PKC.

Flashcard 85: What nucleotide is bound to an inactive G protein alpha subunit?

Answer: GDP. Low-energy state keeps the G protein subunits together and inactive.

Flashcard 86: What occurs during the termination phase of signal transduction?

Answer: The signal is turned off, ending the response. Signal degradation or receptor desensitization stops response.

Flashcard 87: Identify a key characteristic of signal transduction pathways.

Answer: Specificity and regulation of cellular responses. Ensures appropriate cellular responses to external stimuli.

Flashcard 88: Which enzyme terminates cAMP signaling by degrading cAMP?

Answer: Phosphodiesterase (PDE). Breaks down cAMP to stop the signaling response.

Flashcard 89: What enzyme converts ATP into cAMP in many GPCR pathways?

Answer: Adenylyl cyclase. G protein-activated enzyme that synthesizes the second messenger cAMP.

Flashcard 90: Identify a key function of the JAK-STAT signaling pathway.

Answer: To transmit signals from cytokines to the nucleus. Cytokine-activated pathway directly phosphorylating transcription factors.

Flashcard 91: What is the function of a transcription factor in signal transduction?

Answer: To regulate gene expression in response to signals. Protein that controls gene transcription when activated.

Flashcard 92: In which cellular location do steroid hormones typically exert their effects?

Answer: In the nucleus after receptor binding. Steroid-receptor complexes directly regulate transcription.

Flashcard 93: What is the main function of a receptor tyrosine kinase?

Answer: To transfer phosphate groups to tyrosine residues. Autophosphorylation activates kinase domain for downstream signaling.

Flashcard 94: What is signal amplification in a transduction pathway?

Answer: A small input triggers a larger output through multi-step activation. Each step activates many molecules, creating exponential signal growth.

Flashcard 95: Identify the type of signaling where cells communicate over short distances.

Answer: Paracrine signaling. Local signaling between nearby cells via diffusion.

Flashcard 96: What nucleotide replaces GDP to activate a G protein alpha subunit?

Answer: GTP. High-energy nucleotide activates the alpha subunit for signaling.

Flashcard 97: What is the function of a ligand-gated ion channel?

Answer: To open or close in response to a ligand binding. Channel conformational change allows ion permeability.

Flashcard 98: Which type of molecule typically acts as a signal in signal transduction?

Answer: Ligands such as hormones or neurotransmitters. Signaling molecules that bind to specific receptors.

Flashcard 99: Identify the term for one signaling molecule affecting nearby cells.

Answer: Paracrine signaling. Local signaling between cells in the same tissue area.

Flashcard 100: Identify the term for signaling that requires direct cell-to-cell contact.

Answer: Juxtacrine (contact-dependent) signaling. Membrane-bound signals require physical touching between cells.