CELL SIGNALING - BIO EXAM 3

What are the four general types of cell signaling?

Direct contact, paracrine, endocrine, and synaptic signaling.

What happens in direct contact signaling? Give an example.

Cells communicate through cell membrane molecules touching (no release of signal molecule).
Example: Immune cells recognizing antigens via surface receptors.

What happens in paracrine signaling? Give an example.

A cell releases signals that affect nearby target cells.
Example: Growth factors stimulating nearby cells to divide.

What happens in endocrine signaling? Give an example.

Hormones are secreted into the bloodstream to reach distant target cells.
Example: Insulin released by the pancreas affects cells throughout the body.

hat happens in synaptic signaling? Give an example.

A nerve cell releases neurotransmitters across a synapse to a target cell.
Example: Acetylcholine released from neurons to muscle cells.

What are the four general steps of cell signaling?

1) Signal reception
(2) Signal transduction
(3) Cellular response
(4) Signal termination/reset

What occurs during signal reception?

A ligand binds to a specific receptor (either on the cell surface or inside the cell).

What occurs during signal transduction?

The signal is converted into a different form (often through phosphorylation cascades).

What occurs during the cellular response?

The cell performs a specific action (e.g., gene expression change, metabolism change).

What occurs during signal termination?

The signal pathway shuts off to return the cell to its resting state.

What is a ligand?

A signaling molecule that binds to a receptor to activate or inhibit its function.

What is a kinase enzyme?

An enzyme that adds a phosphate group (phosphorylation) to another molecule, often activating it.

What is a phosphatase enzyme?

An enzyme that removes a phosphate group (dephosphorylation), often deactivating the target.

How are kinases and phosphatases involved in cell signaling?

They regulate signal transduction by turning proteins on/off via phosphorylation cascades.

How can the same signal have different effects on different cells?

Different cells may have different receptors, signaling pathways, or target proteins.

Example: Epinephrine causes heart cells to beat faster but liver cells to break down glycogen.

Which ligands use cell-surface receptors?

Hydrophilic or large ligands that cannot cross the membrane, e.g., peptide hormones.

Which ligands use intracellular receptors?

Small or hydrophobic ligands that can diffuse through the membrane, e.g., steroid hormones.

What are ion channel receptors and where are they found?

Ligand-gated channels on the plasma membrane that open/close to let ions pass.
Example: Acetylcholine receptor on muscle cells.

What are receptor kinases and where are they found?

Membrane receptors that act as enzymes (often tyrosine kinases) when activated.
Example: Insulin receptor.

What are G protein-coupled receptors (GPCRs) and where are they found?

Cell surface receptors that activate G proteins when a ligand binds.
Example: Adrenaline receptor.

What are intracellular receptors and where are they found?

Receptors inside the cytoplasm or nucleus that bind small, nonpolar ligands.
Example: Estrogen receptor.

What kind of receptor does insulin bind to, and what does it do?

Insulin binds to a receptor tyrosine kinase on the cell surface.
Effect: Promotes glucose uptake by cells and glycogen storage, lowering blood sugar.

What kind of receptor does glucagon bind to, and what does it do?

Glucagon binds to a G protein-coupled receptor (GPCR) on the cell surface.
Effect: Activates enzymes that break down glycogen, increasing blood sugar.