4 Cell Signaling Free Online FlashCards

What is a ligand in cell signaling?

A ligand is a signaling molecule that binds a specific receptor on or in a target cell.

Why can a ligand affect some cells but not others?

Only cells with the appropriate receptor can respond to a particular ligand.

Which ligands commonly bind cell-surface receptors?

Cell-surface receptors bind ligands that cannot readily cross the plasma membrane, including many peptide hormones and neurotransmitters.

How can an intracellular receptor change gene expression?

Some steroid hormones cross the plasma membrane and bind intracellular receptors; the resulting complex can directly regulate gene expression.

What does a G protein-coupled receptor activate?

A GPCR activates a nearby G protein, which can regulate enzymes or ion channels.

How can ligand binding activate an enzyme-linked receptor?

Ligand binding brings receptor molecules together, activating enzyme activity or recruiting signaling proteins.

How does a ligand-gated ion channel affect a cell?

Ligand binding opens or closes the channel, changing ion flow across the membrane and often rapidly altering the cell’s electrical state.

What are the three stages of a typical signaling pathway?

Reception is ligand binding to a receptor; transduction relays and processes the signal inside the cell; response is the resulting change in cell activity.

How can a signaling pathway amplify a signal?

One activated receptor can lead to the activation of many downstream molecules, increasing the signal’s effect.

What is the sequence from adenylyl cyclase to PKA activation?

Adenylyl cyclase converts ATP into cAMP; cAMP activates PKA, which phosphorylates target proteins.

What is a second messenger?

A second messenger is a small intracellular molecule or ion that carries a signal from an activated receptor to other targets.

What happens when phospholipase C acts on PIP₂?

Phospholipase C splits PIP₂ into IP₃ and DAG. IP₃ can release Ca²⁺ from intracellular stores, while DAG and Ca²⁺ can activate protein kinase C together.