Signaling Molecules and Cellular Receptors

Review Questions

What property 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 and directly influence gene expression upon receptor binding.

Hint:

B

The secretion of hormones by the pituitary gland is an example of _______________.

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

Hint:

C

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 do not need ion channels to move through the membrane.
  4. Ions bind to carrier proteins in the bloodstream, which must be removed before transport into the cell.

Hint:

B

Endocrine signals are transmitted more slowly than paracrine signals because ___________.

  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 don't bind to carrier proteins during transport

Hint:

A

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.

  1. Intracellular
  2. Hormone
  3. Enzyme-linked
  4. Gated ion channel-linked

Hint:

C