1. The molecules bind to the extracellular domain.
2. The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.
3. The molecules are attached to transport proteins that deliver them through the bloodstream to target cells.
4. The ligands are able to penetrate the membrane, directly influencing gene expression upon receptor binding.

1. autocrine signaling
2. direct signaling across gap junctions
3. endocrine signaling
4. paracrine signaling

1. Ions are too large to diffuse through the membrane.
2. Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane.
3. Ions bind to hydrophobic molecules within the ion channels.
4. Ions bind to carrier proteins in the bloodstream, which must be removed before transport into the cell.

1. The ligands are transported through the bloodstream and travel greater distances.
2. The target and signaling cells are close together.
3. The ligands are degraded rapidly.
4. The ligands do not bind to carrier proteins during transport.

1. It binds gated ion channels and causes a flow of ions in the cell.
2. It binds cell surface receptors and activates synthesis of cAMP.
3. It binds to cell surface receptors and activates a phosphorylation cascade.
4. It binds to an intracellular receptor and activates gene transcription.

1. It binds to a G-protein-linked receptor.
2. It binds to a receptor tyrosine kinase.
3. It binds to a gated ion channel.
4. It binds to an intracellular receptor.

Where do DAG and IP₃ originate?

1. They are formed by phosphorylation of cAMP.
2. They are ligands expressed by signaling cells.
3. They are hormones that diffuse through the plasma membrane to stimulate protein production.
4. They are the cleavage products of the inositol phospholipid, PIP₂.

1. They are polar.
2. They are nonpolar.
3. They contain a hydroxyl group.
4. They occur more frequently in the amino acid sequence of signaling proteins.

1. ATP
2. cAMP
3. calcium ions
4. sodium ions

1. A tyrosine kinase enzyme must be activated.
2. GDP is exchanged for GTP.
3. The receptor forms a dimer.
4. The insulin molecule is internalized in the cytoplasm.

1. A phosphatase removes phosphorylated amino acids from proteins.
2. A phosphatase removes the phosphate group from phosphorylated amino acid residues in a protein.
3. A phosphatase phosphorylates serine, threonine, and tyrosine residues.
4. A phosphatase degrades second messengers in the cell.

1. A small, hydrophobic ligand binds to NF-κB, activating it.
2. NF-κB is phosphorylated and is then free to enter the nucleus to bind DNA.
3. NF-κB is a kinase that phosphorylates a transcription factor that binds DNA and promotes protein production.
4. Phosphorylation of the inhibitor IκB dissociates the complex between it and NF-κB, allowing NF-κB to enter the nucleus and stimulate transcription.

1. when a cell is infected by a virus
2. when a cell is damaged
3. when a cell is no longer needed
4. all of the above

1. apoptosis
2. their mechanism of glycolysis
3. the mechanism of protein biosynthesis
4. replication of DNA

1. activation of metabolism
2. cell division
3. inhibition of glucose metabolism by liver cells
4. synthesis of enzymes

1. autoinducer
2. mating factor
3. second messenger
4. steroid

1. a sufficient density of bacteria is present
2. bacteria release growth hormones
3. bacterial protein expression is switched on
4. treatment with antibiotics occurs

1. autocrine
2. endocrine
3. paracrine
4. gap junction

1. An autoinducer allows the producer to act independently of the presence of other cells.
2. An autoinducer does not diffuse away from the cell.
3. An autoinducer allows a positive feedback loop, which increases the response in proportion to the population size.
4. An autoinducer presents no advantage for the cell.

Most antibiotics used in the clinic today function by inhibiting intracellular or membrane proteins found in bacterial cells. Would targeting secreted autoinducers be another viable method of treating bacterial infections? Explain.