Bio 1201 Ch. 11: Cell Communication

What is local regulation?

A process where a cell's activity is controlled within a small region through chemical signals or direct contact with nearby cells.

What are the main ways cells communicate locally?

Through cell junctions such as plasmodesmata (plants) and gap junctions (animals).

What is a ligand-receptor interaction?

A highly specific "lock-and-key" binding between a ligand and its receptor that causes the receptor to change shape.

How does ligand binding initiate a signal-transduction pathway?

The binding changes the receptor's shape, triggering the first steps of the transduction pathway.

Where can receptors be found in target cells?

On the plasma membrane or inside the cell in the cytoplasm or nucleus.

What are G protein-coupled receptors (GPCRs)?

Large family of cell-surface receptors that use G proteins; G protein is inactive when GDP-bound and active when GTP-bound.

What are tyrosine kinase receptors (RTKs)?

Receptors with enzymatic activity that phosphorylate tyrosines; activate multiple pathways; important in growth; malfunction linked to cancers.

What are ligand-gated ion channels?

Receptors that open or close ion channels when a ligand binds; allow specific ions like Na+ or Ca2+ to pass through.

What are intracellular receptors?

Receptors located in the cytosol or nucleus; bind small hydrophobic molecules such as steroid and thyroid hormones; act as transcription factors.

What are local regulators?

Signaling molecules that act over short distances by diffusion; include membrane-bound molecules, glycoproteins, and glycolipids.

How do hormones travel to target cells?

Through the bloodstream; endocrine cells release hormones that bind to receptors on specific target cells.

What are the three stages of cell signaling?

Reception → Transduction → Response.

What happens during reception?

A ligand binds to a receptor on the cell surface or inside the cell.

What happens during transduction?

The signal is relayed through a series of molecular changes, often involving phosphorylation cascades.

What happens during the cellular response?

The cell carries out an action such as activating enzymes or turning genes on/off.

How can the original signal produce a response without entering the cell?

The ligand binds to a receptor, which activates a cascade of proteins inside the cell.

How does phosphorylation propagate signals?

Kinases transfer phosphate groups from ATP to proteins, activating them and passing the signal along.

How do protein phosphatases turn off signaling pathways?

They remove phosphate groups from proteins, inactivating them (dephosphorylation).

What is a second messenger?

A small, water-soluble molecule or ion (such as cAMP or Ca2+) that relays signals inside the cell.

How is cyclic AMP (cAMP) formed?

Adenylyl cyclase converts ATP to cAMP in response to an extracellular signal.

How does cAMP propagate signal information?

It activates protein kinase A, which phosphorylates other proteins in the pathway.

How is cytosolic Ca2+ concentration increased?

Signals trigger release of Ca2+ from intracellular stores, producing strong cellular responses even with small changes.

How are signals transduced into nuclear responses?

Pathways activate transcription factors that turn genes on or off.

How are signals transduced into cytoplasmic responses?

Pathways regulate enzyme activity or metabolic processes.

How is signal amplification achieved?

Enzyme cascades produce many activated molecules from a single signal.

Why do different cells respond differently to the same signal?

Different cells contain different proteins and signaling pathways.

What are scaffolding proteins?

Large proteins that hold pathway components together to increase signal transduction efficiency.