Introduction to Signal-Transduction Pathways

These flashcards are designed to help review and memorize key concepts and details related to signal-transduction pathways, preparing students for their upcoming exam.

What do signal-transduction pathways convert?

They convert external signals (messages) into a physiological response.

What is a second messenger?

A second messenger is a molecule that receives signals from receptors and transmits them inside the cell.

Give an example of a second messenger.

Cyclic AMP (cAMP) is a common example of a second messenger.

What is the primary signaling molecule in epinephrine signaling?

Epinephrine is the primary signaling molecule.

What does the term 'transducer' refer to in the signaling process?

A transducer is typically a receptor that receives the primary message.

What is the role of effectors in a signal-transduction pathway?

Effectors carry out the physiological response initiated by the signal.

Name a common second messenger involved in signaling pathways.

Calcium ion (Ca2+) is a common second messenger.

What is the significance of receptor dimerization in signaling?

Receptor dimerization can enhance the signaling efficiency and specificity.

What type of protein is the insulin receptor?

The insulin receptor is a protein tyrosine kinase.

What activates the insulin receptor?

Insulin binding activates the insulin receptor.

What happens during cross-phosphorylation of the insulin receptor?

Cross-phosphorylation activates the insulin receptor's kinase activity.

How does G protein activation occur in 7TM receptors?

Ligand binding induces a conformational change that activates the associated G protein.

What does adenylate cyclase convert?

Adenylate cyclase converts ATP into cAMP.

What is the effect of cAMP on protein kinase A (PKA)?

cAMP activates PKA by binding to its regulatory subunits.

What do protein kinases do?

Protein kinases phosphorylate specific amino acid residues in target proteins.

What is the role of phospholipase C in signal transduction?

Phospholipase C cleaves PIP2 into IP3 and DAG, which are second messengers.

What does IP3 do in the cell?

IP3 causes the release of Ca2+ from the endoplasmic reticulum.

What is the function of calmodulin?

Calmodulin binds calcium ions and activates various target proteins.

How does insulin facilitate glucose uptake in cells?

Insulin signaling leads to the translocation of glucose transporters to the cell surface.

What role do phosphatases play in signal transduction?

Phosphatases remove phosphate groups from proteins, terminating signals.

What is a common feature of G-protein-coupled receptors?

They contain seven transmembrane helices.

What happens when GTP binds to Gα?

Gα dissociates from Gβγ and from the receptor.

What is a consequence of GTP hydrolysis by Gα?

It leads to the inactivation of Gα and the reassociation with Gβγ.

Describe the role of the epidermal growth factor (EGF).

EGF promotes growth and differentiation of epidermal and epithelial cells.

What does EGF binding to its receptor induce?

It induces receptor dimerization and activation of downstream signaling.

How does the GTPase activity of Ras affect signaling?

Ras's GTPase activity helps to terminate the signaling process.

What do mutations in signal-transduction proteins often lead to?

They can lead to diseases such as cancer.

Identify a sensory system that relies on signal-transduction pathways.

The olfactory system (sense of smell) relies on signal-transduction pathways.

How are calcium ions important in signaling?

Calcium ions act as second messengers that activate various cellular processes.

Describe the action of phosphoinositide 3-kinase (PI3K).

PI3K adds a phosphoryl group to PIP2, producing PIP3 and attracting signaling proteins.

What is the net effect of EGF binding to its receptor?

It activates signaling cascades that lead to increased gene expression and cell growth.

Define agonist in the context of receptor signaling.

An agonist is a molecule that binds to a receptor and activates downstream signaling.

What do antagonists do in signal transduction?

Antagonists block receptor activation and downstream signaling.

Explain the role of diacylglycerol (DAG) in signaling.

DAG acts as a second messenger that activates protein kinase C (PKC).

What is the general function of signal-transduction pathways in cells?

They transmit external signals to elicit a physiological response.

How do sensory receptors initiate signal transduction?

They bind specific molecules, leading to changes in membrane potential and signaling.

What is the impact of cAMP in cellular responses?

cAMP acts as a signaling molecule that mediates various cellular responses.

What does the term ‘downstream’ refer to in signal transduction?

It refers to the pathways and processes that occur as a result of the initial signaling event.

Identify a characteristic feature of GPCRs.

They interact with heterotrimeric G proteins.

What initiates the release of intracellular second messengers?

The binding of extracellular signaling molecules to their receptors.

Describe the consequences of calcium influx in cells.

Increased calcium levels can lead to muscle contraction, neurotransmitter release, and other vital processes.

How does calmodulin function as a relay in signaling pathways?

Calmodulin undergoes conformational changes upon calcium binding to interact with and activate kinases.

What defines the specificity of signal-transduction pathways?

Specificity is determined by the interaction of signaling molecules with specific receptors.

What is the 'fight-or-flight' response?

A physiological response induced by epinephrine signaling, preparing the body for action.

Which second messengers are derived from phosphatidylinositol?

Inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG).

What happens to Gα when bound to GTP?

It dissociates from the βγ dimer and becomes active.

What is the role of G-protein receptor kinases?

They phosphorylate activated receptors to prevent continuous signaling.

How does signal termination occur in G-proteins?

Through intrinsic hydrolysis of GTP to GDP, resulting in inactivation.

What triggers the activation of adenylate cyclase?

Activated Gα stimulates adenylate cyclase to produce cAMP.

Describe the general process of signal transduction.

Signal transduction involves receptor binding, signal amplification, and execution of physiological responses.

What type of receptor does insulins bind to activate signaling?

Insulin binds to a receptor tyrosine kinase.

How is the signaling cascade amplified?

Through the activation of multiple downstream effectors by each activated signaling molecule.

What is required for protein kinase C (PKC) activation?

Both diacylglycerol (DAG) and calcium ions are required for PKC activation.

Explain how epinephrine signaling affects heart muscle.

Epinephrine binding leads to increased cAMP levels, enhancing heart muscle contraction.

What is the role of the activation loop in protein kinases?

The activation loop regulates the accessibility of the kinase active site for substrate binding.

How does insulin signaling promote fat storage?

By enhancing glucose uptake and promoting lipogenesis in adipose tissue.

What is the signaling effect of caffeine on adenosine receptors?

Caffeine blocks adenosine receptors, leading to increased alertness and wakefulness.

Describe the term ‘phosphorylation cascade’.

A series of phosphorylation events that amplify a signaling response.

What happens when calcium binds to calmodulin?

Calmodulin undergoes a conformational change, allowing it to activate target proteins.

What pathway does IP3 activate after its generation?

IP3 stimulates the release of calcium ions from the endoplasmic reticulum.

What is the consequence of receptor dimerization?

It enhances the receptor's ability to interact with and activate downstream signaling proteins.

In the context of signaling, define 'homeostasis'.

Homeostasis refers to the maintenance of stable internal conditions in the body.

What physiological changes occur as a result of stress-induced epinephrine release?

Increased heart rate, heightened blood pressure, and enhanced energy mobilization.

How does Gα switch from active to inactive states?

By hydrolyzing GTP to GDP, leading to its reassociation with Gβγ.

What cellular processes does insulin signaling impact besides glucose uptake?

It also influences fat synthesis and protein synthesis.

Describe the physiological role of diacylglycerol (DAG).

DAG serves as a second messenger that activates protein kinase C (PKC) for signaling.

Explain the concept of 'signal integration' in signaling pathways.

Signal integration refers to the ability of the cell to process multiple signals and produce a coordinated response.

What does the term 'feedback inhibition' refer to in signaling?

Feedback inhibition is the process by which a signaling pathway is regulated by its own output.

What is the effect of activating Gαs proteins?

Activating Gαs stimulates adenylate cyclase, increasing cAMP levels.

Identify the key steps in a typical signaling pathway.

Reception, transduction, response, and termination.

What are some common therapeutic targets in signal-transduction pathways?

Receptors, enzymes, and other proteins involved in the signaling cascade.

What is a key feature of 7TM receptors that interact with G proteins?

They have seven membrane-spanning domains.

How do receptor tyrosine kinases activate signaling cascades?

By autophosphorylating and phosphorylating downstream substrates.

What physiological effects result from activation of protein kinase A (PKA)?

Increased glycogen breakdown and inhibition of glycogen synthesis.

How does EGF facilitate cellular growth?

EGF binding stimulates cell division and growth through downstream signaling.

Explain the term 'signal amplification' in cellular signaling.

Signal amplification occurs when one signaling molecule activates multiple downstream effectors.

What are the consequences of oncogenic mutations in Ras proteins?

They can lead to continuous signaling and uncontrolled cell proliferation.

Describe the role of small G proteins like Ras in signaling pathways.

Small G proteins as molecular switches mediate signaling downstream from receptor activation.

What is the purpose of using second messengers in signal-transduction pathways?

Second messengers facilitate the propagation and amplification of signals within the cell.

How does the body ensure specificity in signaling pathways?

Specificity is maintained by selective receptor-ligand interactions and pathway cross-talk.

What factors can influence the termination of signaling pathways?

Enzymatic degradation, receptor desensitization, and negative feedback mechanisms.

What is the physiological significance of the GTP-GDP cycle?

It regulates the activation and inactivation of G proteins in signaling.

How does light exposure result in visual signal transduction?

Light induces a conformational change in rhodopsin, activating signaling cascades.

What is the function of transducin in vision?

Transducin activates phosphodiesterase, reducing cGMP levels and closing ion channels.

How do cellular responses vary according to the type of receptor activated?

Different receptors trigger distinct signaling cascades leading to unique physiological outcomes.

What is the effect of high glucose levels on insulin signaling?

High glucose levels stimulate insulin secretion to enhance glucose uptake.

What are the key components involved in the phosphoinositide cascade?

Phospholipase C, IP3, DAG, calcium, and protein kinase C.

How can the same signaling molecule produce different effects in different cell types?

Different cells may have different receptors, signaling machinery, and downstream effectors.

What is the role of receptor desensitization in signaling pathways?

It prevents overstimulation of receptors and maintains homeostatic balance.

Identify the role of PIP3 in insulin signaling.

PIP3 recruits and activates proteins that promote glucose uptake.

What are G-protein-coupled receptors (GPCRs)?

GPCRs are a large family of receptors that transduce signals through G proteins.

What initiates the signaling sequence in 7TM receptors?

Binding of a ligand to the receptor initiates the signaling sequence.

What is a potential result of disrupting signal-transduction pathways?

Disruption can lead to diseases such as cancer, metabolic disorders, or neurological conditions.

How do receptor tyrosine kinases regulate cellular functions?

By phosphorylating tyrosine residues on themselves and their substrates to induce signaling.

What are the common types of signaling molecules in the body?

Hormones, neurotransmitters, and growth factors are common signaling molecules.

What do the terms 'upstream' and 'downstream' refer to in signal transduction?

'Upstream' refers to early components of the pathway, while 'downstream' refers to later components.

What happens to the ion channels in photoreceptor cells during light exposure?

Light exposure causes ion channels to close, leading to hyperpolarization of the cells.

Explain how G protein signaling is reset.

It is reset when GTP is hydrolyzed to GDP, returning G proteins to their inactive state.

What physiological process does insulin-triggered signaling primarily promote?

Glucose uptake and storage in tissues.

What happens during the termination phase of signal transduction?

Signals are turned off to prevent over-activation and to restore baseline cellular function.