Cell Signaling: Pathways, Receptors, and Responses in Biology

What are the three stages of cell signaling?

Reception, transduction, and response.

What is the role of kinases in signal transduction?

Kinases are enzymes that phosphorylate molecules, often forming a phosphorylation cascade.

What is a phosphorylation cascade?

A series of events where one kinase activates another, amplifying the signal.

What are secondary messengers?

Small, non-protein molecules or ions that help relay signals within the cell.

How does cyclic AMP (cAMP) function in signaling?

cAMP is activated by adenyl cyclase and acts as a secondary messenger to trigger cellular responses.

What is the function of calcium ions in cell signaling?

Calcium ions can enter the cell and trigger various cellular responses, often through IP3 pathways.

What happens when a signaling molecule binds to a receptor?

It activates a series of intracellular processes, leading to a cellular response.

What is the significance of signal amplification in cell signaling?

It allows a small signal to produce a large cellular response, enhancing the effectiveness of the signal.

What is cross talk in signaling pathways?

Interaction between different signaling pathways that can enhance or inhibit each other's responses.

How do scaffolding proteins contribute to signaling pathways?

They organize and stabilize signaling complexes, improving the efficiency and speed of signal transduction.

What is the role of protein phosphatases in signaling?

They inactivate phosphorylated proteins, terminating the signaling pathway.

What is the first messenger in cell signaling?

The ligand that binds to a receptor to initiate the signaling process.

Describe the process of signal termination.

Involves reverting receptors to inactive forms and hydrolyzing GTP on G proteins to GDP.

What is the function of phospholipase C in signaling?

It cleaves PIP2 into DAG and IP3, which are involved in generating secondary messengers.

What is the relationship between signal transduction pathways and protein interactions?

Cell signaling relies heavily on protein interactions to relay and amplify signals.

How do different cell types respond to the same signal?

Different cells can activate different sets of genes, leading to varied responses.

What is the significance of having multiple receptors for the same ligand?

It allows for diverse responses in different cell types and contexts.

What is the role of epinephrine in cell signaling?

Epinephrine triggers the breakdown of glycogen into glucose in response to stress.

What is the advantage of multistep signal transduction pathways?

They provide amplification, control, and coordination of cellular responses.

What occurs when signaling molecules are diluted?

Dilute ligands may struggle to trigger rapid and large cellular responses.

What happens during the activation of GPCRs?

They bind to G proteins and activate them, leading to downstream signaling events.

How does the binding of IP3 affect calcium ion levels?

IP3 binds to channels in the ER, causing calcium ions to flow out and increase cytosolic concentration.

What is the importance of cellular responses in signaling?

Cellular responses allow organisms to adapt to changing environments and conditions.

What are the three stages of signal transduction?

Reception, Transduction, and Response.

How do cells communicate locally?

Through specialized cell junctions, paracrine signaling, and synaptic signaling.

What is paracrine signaling?

A form of local signaling where signaling chemicals act on nearby target cells.

What role do hormones play in cell signaling?

Hormones are made by one tissue and perceived by cells in another tissue, facilitating long-distance signaling.

What initiates the response in signal reception?

A signaling molecule binds to a protein receptor, causing it to change shape and initiate a response.

What is a ligand in the context of cell signaling?

A signaling molecule that binds to a specific receptor to activate it.

What are G protein-coupled receptors (GPCRs)?

Transmembrane receptors that work with G proteins to transmit signals from outside to inside the cell.

How does a G protein become activated?

When a ligand binds to a GPCR, it causes a conformational change that allows GDP to be replaced by GTP.

What happens after a G protein is activated?

The activated G protein dissociates from the receptor and activates an enzyme, often producing cyclic AMP as a secondary messenger.

What is quorum sensing?

A mechanism by which bacteria secrete chemicals to monitor local population density and coordinate behavior.

What types of receptors can be found in cells?

Integral membrane proteins like G protein-coupled receptors, receptor tyrosine kinases, and ion channel receptors.

What is the significance of receptor specificity?

Specific receptors bind only to specific signaling molecules, ensuring precise communication.

What are the general types of responses triggered by signal transduction?

Responses can include gene expression, enzyme catalysis, and cytoskeletal rearrangement.

What is the role of secondary messengers in signal transduction?

They amplify the signal inside the cell and help propagate the response initiated by the receptor.

What is the function of gap junctions in cell signaling?

They allow direct communication between adjacent cells through the passage of signaling molecules.

What is the effect of toxins on G protein function?

Toxins from bacteria can interfere with G protein function, blocking signal transmission and causing disease.

What is the difference between local and long-distance signaling?

Local signaling occurs between nearby cells, while long-distance signaling involves hormones acting on distant cells.

What is the role of the cytoskeleton in cell signaling responses?

It can be rearranged as part of the cellular response to signaling pathways.

What is the significance of the three types of receptors mentioned?

They allow cells to perceive and respond to a variety of chemical signals in different ways.

What determines how often a ligand is bound and causes signaling?

The ligand concentration outside the cell.

What happens to GTP in the G protein signaling pathway?

The G protein hydrolyzes GTP to GDP + Pi, inactivating itself.

What are G protein coupled receptors (GPCRs) involved in?

They are involved in signaling for smell and taste, and THC exerts effects through the CB1 GPCR.

How many odorant GPCR receptors do humans have compared to dogs?

Humans have ~400, while dogs have ~1100.

What do receptor tyrosine kinases (RTKs) catalyze?

The transfer of phosphate groups from ATP to the amino acid tyrosine.

What is the state of RTKs when inactive?

They are monomers embedded in the membrane by a single alpha helix.

What is dimerization in the context of RTKs?

The process where two monomers come together when a ligand binds, activating the receptor.

What occurs after dimerization of RTKs?

Each tyrosine kinase adds a phosphate group from ATP to a tyrosine on the cytoplasmic domain, activating the receptor.

What are the phosphorylated tyrosines on RTKs used for?

They act as docking sites for relay proteins to bind and become activated.

What basic cell functions do RTKs regulate in humans?

Cell division, differentiation into different cell types, and cell survival.

What happens when a signaling ligand binds to a ligand-gated ion channel?

The channel opens or closes, allowing or blocking the flow of specific ions.

What is the role of transcription factors in intracellular receptor signaling?

They bind DNA at specific sequences to turn on the transcription of specific genes.

What is apoptosis?

Programmed cell death, where cellular agents chop up and recycle cell components.

What initiates apoptosis via RTKs?

Signal molecules from outside the cell bind to RTKs, triggering a signal transduction pathway.

What are caspases?

Specific proteases that break up proteins during apoptosis.

What role does cytochrome c play in apoptosis?

It acts as a 'death ligand' if released from the mitochondria.

What is one pathway for apoptosis that involves mitochondrial proteins?

It triggers the formation of holes in the outer mitochondrial membrane, releasing proteins that promote apoptosis.

How can internal signals trigger apoptosis?

They can arise from the nucleus when DNA is irreparably damaged or from the ER due to misfolded proteins.

What is the significance of apoptosis in development?

It is important for processes like digit formation.