recap

7.4 recap

145

Cells respond to signal transduction by opening membrane channels, activating or inactivating enzymes, and stimulating or inhibiting gene transcription.

learning outcomes

You should be able to:

  • Describe the signal transduction pathway stimulated by oxytocin.

  • Compare various mechanisms that cells use to respond to signals.

Question 1

How does oxytocin signaling involve several signaling pathways?

Oxytocin is involved with both G protein–linked and ion channel responses. It binds to a G protein–linked receptor (see Figure 7.7), resulting in signal transduction through the IL3–DAG pathway, which releases Ca2+ into the cytoplasm via ion channels. In the brain, the effect of Ca2+ is to indirectly stimulate nerve cell activity by the opening of ion channels for Na+.

Question 2

Which method(s) of cell response to signaling are rapid and which are slower? Explain.

Ion channel opening is a rapid response to signaling. Enzyme modification is also a relatively rapid response mechanism. Changes in gene expression involve many steps, so cell signaling via transcription factors is slower.

We have described how signals from a cell’s environment can influence the cell. But the environment of a cell in a multicellular organism is more than the extracellular medium—it includes neighboring cells as well. In the next section we’ll see how specialized junctions between cells allow them to pass signals from one to another.