Review Questions

Review Questions

Which of the following properties prevents the ligands of cell-surface receptors from entering the cell?
  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.
The secretion of hormones by the pituitary gland is an example of which type of signaling?
  1. autocrine signaling
  2. direct signaling across gap junctions
  3. endocrine signaling
  4. paracrine signaling
Why are ion channels necessary to transport ions into or out of a cell?
  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.
Why are endocrine signals transmitted more slowly than paracrine signals?
  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.
Aldosterone is a steroid hormone that regulates reabsorption of sodium ions in the kidney tubular cells. What is the probable mechanism of action of aldosterone?
  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.
The gas nitric oxide has been identified as a signaling molecule. Which of the following mechanisms of action would you expect from a gaseous molecule?
  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.
What property enables the residues of the amino acids serine, threonine, and tyrosine to be phosphorylated?
  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.
Dopamine is a neurotransmitter in the brain that causes long-term responses in neurons and binds to a G-protein-linked receptor. Which of the following chemicals would you expect to increase in concentration after dopamine binds its receptor?
  1. ATP
  2. cAMP
  3. calcium ions
  4. sodium ions
The hormone insulin binds to a receptor tyrosine kinase on the surface of target cells. Which of the following steps takes place before phosphorylation of tyrosine residues?
  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.
What is the function of a phosphatase?
  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.
How does NF-κB induce gene expression?
  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.
Apoptosis can occur in a cell under what conditions?
  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
Cancer cells that continue to divide when defective often show changes in what cellular function?
  1. apoptosis
  2. their mechanism of glycolysis
  3. the mechanism of protein biosynthesis
  4. replication of DNA
Epinephrine mediates the fight-or-flight response of the body. One of the effects is to increase the amount of glucose available to muscles. What does the signaling pathway triggered by epinephrine cause to occur in liver cells?
  1. activation of metabolism
  2. cell division
  3. inhibition of glucose metabolism by liver cells
  4. synthesis of enzymes
Which type of molecule acts as a signaling molecule in yeasts?
  1. autoinducer
  2. mating factor
  3. second messenger
  4. steroid
When is quorum sensing triggered to begin?
  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
Yeast releasing mating factor can be classified as which type of signal?
  1. autocrine
  2. endocrine
  3. paracrine
  4. gap junction
The bioluminescent bacteria Vibrio fischeri produces luminescence only if the population reaches a certain density. What is the advantage of an autoinducer?
  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.