92 Review Questions
5. What property prevents the ligands of cell-surface receptors from entering the cell?
- The molecules bind to the extracellular domain.
- The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.
- The molecules are attached to transport proteins that deliver them through the bloodstream to target cells.
- The ligands are able to penetrate the membrane and directly influence gene expression upon receptor binding.
6. The secretion of hormones by the pituitary gland is an example of _______________.
- autocrine signaling
- paracrine signaling
- endocrine signaling
- direct signaling across gap junctions
7. Why are ion channels necessary to transport ions into or out of a cell?
- Ions are too large to diffuse through the membrane.
- Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane.
- Ions do not need ion channels to move through the membrane.
- Ions bind to carrier proteins in the bloodstream, which must be removed before transport into the cell.
8. Endocrine signals are transmitted more slowly than paracrine signals because ___________.
- the ligands are transported through the bloodstream and travel greater distances
- the target and signaling cells are close together
- the ligands are degraded rapidly
- the ligands don’t bind to carrier proteins during transport
9. A scientist notices that when she adds a small, water-soluble molecule to a dish of cells, the cells turn off transcription of a gene. She hypothesizes that the ligand she added binds to a(n) ______ receptor.
- Intracellular
- Hormone
- Enzyme-linked
- Gated ion channel-linked
10. Where do DAG and IP3 originate?
- They are formed by phosphorylation of cAMP.
- They are ligands expressed by signaling cells.
- They are hormones that diffuse through the plasma membrane to stimulate protein production.
- They are the cleavage products of the inositol phospholipid, PIP2.
11. What property enables the residues of the amino acids serine, threonine, and tyrosine to be phosphorylated?
- They are polar.
- They are non-polar.
- They contain a hydroxyl group.
- They occur more frequently in the amino acid sequence of signaling proteins.
12. Histamine binds to the H1 G-protein-linked receptor to initiate the itchiness and airway constriction associated with an allergic response. If a mutation in the associated G-protein’s alpha subunit prevented the hydrolysis of GTP how would the allergic response change?
- More severe allergic response compared to normal G-protein signaling.
- Less severe allergic response compared to normal G-protein signaling.
- No allergic response.
- No change compared to normal G-protein signaling.
13. A scientist observes a mutation in the transmembrane region of EGFR that eliminates its ability to be stabilized by binding interactions during dimerization after ligand binding. Which hypothesis regarding the effect of this mutation on EGF signaling is most likely to b