Introduction to Signal Transduction - AP Biology

What are the two second messengers produced when PIP $_2$ is cleaved?

IP $_3$ and DAG. Two different second messengers produced from one membrane lipid.
What are the three classic stages of cell signaling in order?

Reception, transduction, response. Standard pathway: detect signal, process it, then act on it.
What role do G-proteins play in signal transduction?

They transmit signals from receptors to enzymes. Act as molecular switches linking receptors to effectors.
What is a cell-surface receptor used for?

Detecting extracellular hydrophilic signals at the plasma membrane. Water-soluble signals can't cross membranes so need surface receptors.
Identify the second messenger produced by adenylyl cyclase.

cAMP. Cyclic adenosine monophosphate, a major signaling molecule in cells.
What is the significance of receptor dimerization in signal transduction?

It activates receptor tyrosine kinases. Two receptors pair to activate their kinase domains.
What is the result of signal amplification in a pathway?

A small signal produces a large cellular response. Each step multiplies signal strength exponentially.
What is a receptor in cell signaling?

A protein that binds a ligand and initiates signal transduction. Detects specific ligands and starts the signaling cascade inside cells.
Which property of a ligand usually determines whether it crosses the membrane unaided?

Hydrophobic (nonpolar) ligands cross; hydrophilic ligands do not. Polar molecules can't cross lipid membranes without transport proteins.
Define 'second messenger' in the context of signal transduction.

Small molecules that relay signals inside the cell. Intracellular messengers that amplify receptor signals.
Identify the term for one signaling molecule affecting nearby cells.

Paracrine signaling. Local signaling between cells in the same tissue area.
What is the primary role of DAG in many signaling pathways?

It helps activate protein kinase C (PKC) at the membrane. Lipid second messenger that works with calcium to activate PKC.
Which molecule is a key component of the IP3/DAG pathway?

Inositol triphosphate (IP3). Second messenger that triggers calcium release from ER.
Identify the most direct effect of a loss-of-function mutation in a receptor protein.

Reduced or absent cellular response to that ligand. Non-functional receptor cannot detect or respond to its ligand.
Identify the membrane phospholipid that is cleaved to form IP $_3$ and DAG.

PIP $_2$ (phosphatidylinositol 4,5-bisphosphate). Membrane lipid substrate that gets cleaved by phospholipase C enzyme.
What is the role of protein phosphatases in signal transduction?

They remove phosphate groups from proteins to regulate signaling. Dephosphorylation reverses kinase effects to terminate or modulate signaling.
What is the function of calmodulin in Ca $^{2+}$ signaling?

A Ca $^{2+}$ -binding protein that activates target enzymes and proteins. Calcium sensor protein that changes shape when bound to calcium.
What enzyme converts ATP into cAMP in many GPCR pathways?

Adenylyl cyclase. G protein-activated enzyme that synthesizes the second messenger cAMP.
Identify the initial step in a signal transduction pathway.

Signal reception by a receptor protein. First step where signaling molecule binds to receptor.
Identify the term for signaling that requires direct cell-to-cell contact.

Juxtacrine (contact-dependent) signaling. Membrane-bound signals require physical touching between cells.
Which molecules are often targets of phosphorylation in signal transduction?

Serine, threonine, and tyrosine residues. Amino acid residues modified by kinases for regulation.
What is a second messenger in cell signaling?

A small intracellular molecule that relays and amplifies a signal. Diffusible molecules that spread signals throughout the cell interior.
What is the main function of the MAP kinase pathway?

To regulate gene expression and cell division. Phosphorylation cascade controlling cell growth and differentiation.
Identify a key function of the JAK-STAT signaling pathway.

To transmit signals from cytokines to the nucleus. Cytokine-activated pathway directly phosphorylating transcription factors.
What happens during signal transduction when a ligand binds to a receptor?

The receptor undergoes a conformational change. Shape change allows receptor to interact with other proteins.
Describe the role of scaffolding proteins in signal transduction.

They enhance the efficiency of signal transduction. Organize signaling proteins for faster interactions.
What is the primary effect of an ion channel-linked receptor once activated?

It allows ion flow across the membrane. Ligand binding opens channel for specific ion movement.
What is autophosphorylation in an RTK?

The receptor phosphorylates its own tyrosine residues after activation. Activated receptor adds phosphates to its own tyrosine amino acids.
Which type of response is typically faster: altering enzyme activity or altering gene expression?

Altering enzyme activity is typically faster. Protein modification occurs immediately; gene expression requires transcription time.
Identify the receptor class that dimerizes and autophosphorylates on tyrosines.

Receptor tyrosine kinase (RTK). Ligand binding causes two receptors to pair and cross-phosphorylate.
What is the main function of a receptor tyrosine kinase?

To transfer phosphate groups to tyrosine residues. Autophosphorylation activates kinase domain for downstream signaling.
What is the role of the Ras protein in signal transduction?

To relay signals from receptor tyrosine kinases. GTPase that activates MAP kinase cascades downstream.
Identify the term for a cell signaling to itself by secreting a ligand it also detects.

Autocrine signaling. Self-signaling allows cells to regulate their own activity.
What is a ligand in cell signaling?

A signaling molecule that binds to a receptor. The signal molecule that triggers cellular responses by receptor binding.
What is a phosphorylation cascade?

Sequential activation of kinases via phosphorylation. Each active kinase phosphorylates multiple downstream kinases for amplification.
What immediate effect occurs when a ligand opens a ligand-gated ion channel?

Ion flow changes membrane potential and/or cytosolic ion levels. Changed electrical properties trigger rapid cellular responses.
Which enzyme is activated by cAMP in many signal transduction pathways?

Protein kinase A (PKA). cAMP-activated kinase that phosphorylates target proteins.
Identify the type of signaling where cells communicate over short distances.

Paracrine signaling. Local signaling between nearby cells via diffusion.
What is the primary function of a signal transduction pathway?

To convert an external signal into a cellular response. Converts extracellular stimuli into intracellular responses.
Identify a common second messenger in signal transduction pathways.

cAMP (cyclic adenosine monophosphate). Universal second messenger activated by adenylyl cyclase.
What is the role of adenylyl cyclase in signal transduction?

It converts ATP to cAMP. G-protein activated enzyme producing cAMP second messenger.
Identify a receptor type that is intracellular.

Steroid hormone receptors. Lipophilic hormones cross membrane to bind inside cell.
Define 'ligand' in the context of cell signaling.

A molecule that binds specifically to a receptor. Signal molecule with specific receptor binding affinity.
What is the role of diacylglycerol (DAG) in signal transduction?

It acts as a second messenger with IP3. Lipid messenger that activates protein kinase C.
Identify a key characteristic of signal transduction pathways.

Specificity and regulation of cellular responses. Ensures appropriate cellular responses to external stimuli.
What nucleotide is bound to an inactive G protein alpha subunit?

GDP. Low-energy state keeps the G protein subunits together and inactive.
What is the function of a transcription factor in signal transduction?

To regulate gene expression in response to signals. Protein that controls gene transcription when activated.
In which cellular location do steroid hormones typically exert their effects?

In the nucleus after receptor binding. Steroid-receptor complexes directly regulate transcription.
What is signal amplification in a transduction pathway?

A small input triggers a larger output through multi-step activation. Each step activates many molecules, creating exponential signal growth.
What nucleotide replaces GDP to activate a G protein alpha subunit?

GTP. High-energy nucleotide activates the alpha subunit for signaling.
What is the function of a ligand-gated ion channel?

To open or close in response to a ligand binding. Channel conformational change allows ion permeability.
Which type of molecule typically acts as a signal in signal transduction?

Ligands such as hormones or neurotransmitters. Signaling molecules that bind to specific receptors.
Identify the term for long-distance signaling via hormones in the bloodstream.

Endocrine signaling. Hormones travel through circulation to reach distant target cells.
Identify the role of calmodulin in calcium-mediated signaling.

It binds calcium and activates various proteins. Calcium-binding protein that activates target enzymes.
What is signal transduction in cell communication?

Conversion of an external signal into a specific cellular response. Cells detect external signals and produce specific internal responses.
What is a cellular response to signaling, at the molecular level?

A change in protein activity and/or gene expression. Signaling changes what proteins do or which genes are expressed.
Identify the primary protein kinase activated by cAMP in many pathways.

Protein kinase A (PKA). cAMP-dependent enzyme that phosphorylates target proteins for cellular responses.
Which enzyme terminates cAMP signaling by degrading cAMP?

Phosphodiesterase (PDE). Breaks down cAMP to stop the signaling response.
Identify the role of nitric oxide in cell signaling.

It acts as a signaling molecule in various pathways. Gaseous messenger that diffuses freely across membranes.
Name a type of receptor that is also an enzyme.

Receptor tyrosine kinases. Dual-function proteins with catalytic activity when activated.
What is the function of phosphatases in signal transduction?

They remove phosphate groups from proteins. Reverse kinase action by dephosphorylating proteins.
Identify the most direct effect of a constitutively active receptor mutation.

Pathway activation occurs even without ligand binding. Always-active receptor signals continuously regardless of ligand presence.
What is the outcome of a ligand binding to a G-protein-coupled receptor?

Activation of a G-protein. Conformational change activates the G-protein signaling cascade.
What occurs during the termination phase of signal transduction?

The signal is turned off, ending the response. Signal degradation or receptor desensitization stops response.
Which type of signaling involves hormones traveling through the bloodstream?

Endocrine signaling. Long-distance signaling via circulatory system transport.
What is the primary purpose of a signal transduction cascade?

To amplify the signal and ensure a specific response. Sequential protein interactions amplify and direct signal.
What is the role of a protein kinase in signal transduction?

To phosphorylate proteins, altering their activity. Adds phosphate groups to activate/deactivate proteins.
Which option best predicts the effect of inhibiting protein phosphatases in a pathway?

Phosphorylated signaling proteins persist longer, prolonging signaling. Without dephosphorylation, active phosphoproteins accumulate and maintain signaling.
Identify the main receptor class that forms an ion channel when activated.

Ligand-gated ion channel receptor. Opens ion channels directly when ligand binds to receptor.
Which option best explains why the same signal can cause different responses in different cells?

Different cells have different receptors and intracellular signaling proteins. Cell-specific proteins determine how each cell interprets the same signal.
Which molecule is commonly involved in autocrine signaling?

Growth factors. Molecules that stimulate the same cell that secreted them.
What is the primary effect of IP $_3$ in many animal cells?

It triggers Ca $^{2+}$ release from the endoplasmic reticulum. Mobilizes stored calcium from internal organelles into the cytosol.
What is the role of protein kinases in signal transduction?

They transfer phosphate groups to target proteins to alter activity. Phosphorylation changes protein shape and function to propagate signals.
What is an intracellular receptor used for?

Binding small hydrophobic ligands inside the cell to regulate activity. Lipid-soluble molecules can enter cells and bind internal proteins.
What ends signaling by a G protein alpha subunit?

Hydrolysis of GTP to GDP by the alpha subunit (GTPase activity). Built-in enzyme activity returns G protein to inactive state.
What role does calcium play as a second messenger?

It regulates various cellular processes. Controls muscle contraction, enzyme activity, and gene expression.
Identify the second messenger that is a common ligand-gated ion in signaling.

Ca $^{2+}$ . Calcium ion serves as both messenger and direct activator.
Which type of signaling involves direct contact between cells?

Juxtacrine signaling. Cell-to-cell contact signaling via membrane-bound molecules.
Identify the purpose of feedback inhibition in signal transduction.

To regulate and maintain cellular responses. Prevents excessive signaling by inhibiting pathway components.
Identify the receptor class that activates a G protein upon ligand binding.

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

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