cell signaling

What are the three stages of cell signaling?

Reception, transduction, and cellular response.

What happens during reception?

A signaling molecule binds to its specific receptor.

What happens during signal transduction?

The signal is relayed through molecular interactions inside the cell.

What happens during the cellular response?

The cell changes its activity in response to the signal.

What is a signaling molecule?

A molecule that carries a message between cells or to itself.

What is a ligand?

A signaling molecule that binds specifically to a receptor.

What is a receptor?

A protein that recognizes and binds a specific signaling molecule.

What is a target cell?

A cell with the receptor needed to respond to a particular signal.

Where are receptors located?

On the plasma membrane or inside the cell.

What is local signaling?

Communication between nearby cells over short distances.

What is paracrine signaling?

A cell releases signals that affect nearby target cells.

What are growth factors?

Signals that regulate cell growth, division, or survival.

What are cytokines?

Signaling proteins that regulate immune responses, inflammation, and cell activity.

What is autocrine signaling?

A cell releases a signal that binds to receptors on itself.

What is synaptic signaling?

A neuron releases neurotransmitters across a synapse to a target cell.

What is a synapse?

The junction where a neuron communicates with another cell.

What are neurotransmitters?

Chemical messengers released by neurons that bind receptors on target cells.

What is endocrine signaling?

Hormones travel through the bloodstream to distant target cells.

Define hormone.

A chemical messenger released by endocrine cells that travels to target cells, usually through the blood.

How do paracrine and endocrine signaling differ?

Paracrine signals act locally; endocrine hormones travel to distant targets.

How do synaptic and endocrine signaling differ?

Synaptic signals cross a synapse; endocrine hormones travel through the bloodstream.

Why don't all cells respond to the same hormone?

Only cells with compatible receptors can respond to that hormone.

What are the three major receptor types?

Intracellular receptors, ligand-gated ion channels, and G protein-coupled receptors (GPCRs).

What is an intracellular receptor?

A receptor in the cytoplasm or nucleus that binds a signaling molecule inside the cell.

Where are intracellular receptors found?

In the cytoplasm or nucleus.

How can a signaling molecule reach an intracellular receptor?

It crosses the plasma membrane, usually by diffusing through the lipid bilayer.

What kinds of signals commonly bind intracellular receptors?

Hydrophobic molecules, including steroid hormones such as testosterone.

Why can testosterone cross the plasma membrane?

It is lipid-soluble and can diffuse through the membrane.

What happens when a hormone binds an intracellular receptor?

The hormone-receptor complex can regulate gene transcription.

How can an intracellular receptor cause a response?

It changes gene expression, which can alter protein production.

What happens if a cell lacks the appropriate receptor?

It cannot produce that receptor-mediated response to the signal.

What is a ligand-gated ion channel?

A membrane receptor that opens or closes an ion channel when a ligand binds.

What is an ion channel?

A membrane protein that allows specific ions to cross the plasma membrane.

What do ions pass through in ligand-gated channel signaling?

An ion channel protein embedded in the plasma membrane.

Why can't charged ions freely cross the lipid bilayer?

The hydrophobic membrane interior blocks most charged particles.

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

The channel changes shape and opens or closes, altering ion movement.

What happens when ions move through an opened channel?

Membrane voltage or ion concentrations change, potentially triggering a response.

What determines which ions pass through a channel?

The channel's selectivity for particular ions.

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

A membrane receptor that activates an associated G protein when a ligand binds.

Where are GPCRs located?

Embedded in the plasma membrane.

What is a G protein?

A signaling protein that binds GDP and GTP to relay signals.

What is GTP?

Guanosine triphosphate, a nucleotide that activates many G proteins.

What is GDP?

Guanosine diphosphate, the nucleotide associated with the inactive state of many G proteins.

How is a G protein activated?

It exchanges GDP for GTP.

What does an activated G protein do?

It regulates a target protein, such as an enzyme or ion channel.

How does a G protein become inactive?

It hydrolyzes GTP to GDP.

How do GPCRs and ligand-gated ion channels differ?

GPCRs activate G proteins; ligand-gated channels directly control ion passage.

How do GPCRs and intracellular receptors differ?

GPCRs activate membrane-associated signaling pathways; intracellular receptors can regulate gene expression.

What is the basic sequence of GPCR signaling?

Ligand binds GPCR → G protein activates → target protein changes activity → response.

What is a signal transduction pathway?

A series of molecular interactions that relays a signal from a receptor to cellular targets.

What are relay molecules?

Intracellular molecules that pass a signal from one component to another.

What is a signaling cascade?

A sequence of activated molecules that passes a signal through a cell.

What is signal amplification?

One activated molecule activates many downstream molecules, increasing the signal's effect.

Why is signal amplification useful?

A small amount of signal can produce a large cellular response.

What is protein phosphorylation?

The addition of a phosphate group to a protein.

What is a protein kinase?

An enzyme that transfers a phosphate group, usually from ATP, to a target protein.

What is a protein phosphatase?

An enzyme that removes phosphate groups from proteins.

What is dephosphorylation?

The removal of a phosphate group from a molecule.

How can phosphorylation change protein activity?

It can alter a protein's shape, interactions, location, or activity.

Does phosphorylation always activate a protein?

No. It can activate or inhibit a protein depending on the pathway.

How do kinases and phosphatases work together?

Kinases add phosphate groups; phosphatases remove them.

What is a phosphorylation cascade?

A sequence in which activated kinases phosphorylate downstream proteins.

What is ATP's role in phosphorylation?

ATP supplies the phosphate group transferred by a kinase.

What is a second messenger?

A small intracellular molecule or ion that relays and often amplifies a signal.

What is cAMP?

Cyclic AMP, a second messenger that activates protein kinase A in many pathways.

What does cAMP stand for?

Cyclic adenosine monophosphate.

How is cAMP produced?

Adenylyl cyclase converts ATP into cAMP.

What does adenylyl cyclase do?

It produces cAMP from ATP.

How can cAMP amplify a signal?

It activates downstream signaling molecules, including protein kinase A.

How do first and second messengers differ?

A first messenger binds a receptor; a second messenger relays the signal inside the cell.

How can GPCRs activate second-messenger pathways?

Activated GPCRs can stimulate pathways that produce messengers such as cAMP.

What is the difference between transduction and amplification?

Transduction relays a signal; amplification increases its magnitude.

What is homeostasis?

Maintaining relatively stable internal conditions despite changing circumstances.

What is insulin's role in blood glucose regulation?

It lowers blood glucose by promoting glucose uptake and storage.

What is glucagon's role in blood glucose regulation?

It raises blood glucose by stimulating glycogen breakdown and glucose production.

Which organ releases insulin and glucagon?

The pancreas.

Which cells release insulin?

Pancreatic beta cells.

Which cells release glucagon?

Pancreatic alpha cells.

What stimulates insulin secretion?

Rising blood glucose, such as after a meal.

What stimulates glucagon secretion?

Falling blood glucose, such as during fasting.

What happens to blood glucose after a meal?

It rises, stimulating insulin secretion and glucose uptake and storage.

What happens to blood glucose during fasting?

Glucagon helps restore blood glucose by stimulating glucose release and production.

How does insulin affect glycogen storage?

It promotes glycogen synthesis, especially in liver and muscle cells.

How does glucagon affect liver glycogen?

It stimulates glycogen breakdown, helping release glucose into the blood.

How do insulin and glucagon work together?

Their opposing effects help maintain blood glucose homeostasis.

What is glycogen?

A storage polysaccharide made of glucose units, found mainly in liver and muscle.

How does epinephrine signal to liver cells?

It binds adrenergic receptors and activates pathways that promote glycogen breakdown.

How can epinephrine affect airway smooth muscle?

It can relax airway smooth muscle and widen the airways.

How can epinephrine affect blood vessel smooth muscle?

Activation of alpha-adrenergic receptors can cause vasoconstriction in certain vessels.

Why can epinephrine produce different effects in different tissues?

Cells express different receptor subtypes and intracellular signaling proteins.

Do different epinephrine receptors activate identical pathways?

No. Different receptor types can activate different pathways and responses.

What is the general sequence of epinephrine signaling?

Epinephrine binds a receptor → intracellular signaling activates → the cell responds.

What does epinephrine demonstrate about receptor specificity?

The response depends on the receptor and signaling machinery in the target cell.

What is the MAPK signaling pathway?

A kinase cascade involved in cell growth, division, differentiation, and survival.

How can abnormal signaling contribute to cancer?

Mutations can keep growth-promoting pathways active, causing uncontrolled division or survival.

Why can signaling pathways be targets for cancer treatment?

Some treatments target abnormal receptors or proteins that drive cancer growth.

What can happen if a growth-promoting signaling protein is permanently active?

It may continuously stimulate cell growth and division without the normal signal.

Why is receptor specificity important?

It ensures that cells respond to signals they are equipped to detect.

What happens if a ligand cannot bind its receptor?

That ligand generally cannot activate the receptor-mediated pathway.

What is the main idea of cell communication?

Cells detect specific signals, relay them through pathways, and produce coordinated responses.