Question

how cells can:

o Adjust their sensitivity to a signal: e.g. receptor down-regulation, receptor sequestration

Answer 1

Cells typically receive signals in chemical form via various signaling molecules. When a signaling molecule joins with an appropriate receptor on a cell surface, this binding triggers a chain of events that not only carries the signal to the cell interior, but amplifies it as well. Cells can also send signaling molecules to other cells.

What Kind of Signals Do Cells Receive?

• Most cell signals are chemical in nature. For example, prokaryotic organisms have sensors that detect nutrients and help them navigate toward food sources.
• In multicellular organisms, growth factors, hormones, neurotransmitters, and extracellular matrix components are some of the many types of chemical signals cells use
• Some cells also respond to mechanical stimuli. For example, sensory cells in the skin respond to the pressure of touch, whereas similar cells in the ear react to the movement of sound waves.
• In addition, specialized cells in the human vascular system detect changes in blood pressure — information that the body uses to maintain a consistent cardiac load

How Do Cells Recognize Signals?

• Cells have proteins called receptors that bind to signaling molecules and initiate a physiological response.
• Different receptors are specific for different molecules.
• Dopamine receptors bind dopamine, insulin receptors bind insulin, nerve growth factor receptors bind nerve growth factor, and so on.
• In fact, there are hundreds of receptor types found in cells, and varying cell types have different populations of receptors.
• Receptors can also respond directly to light or pressure, which makes cells sensitive to events in the atmosphere.

How Do Cells Respond to Signals?

• Once a receptor protein receives a signal, it undergoes a conformational change, which in turn launches a series of biochemical reactions within the cell.
• These intracellular signaling pathways, also called signal transduction cascades, typically amplify the message, producing multiple intracellular signals for every one receptor that is bound.
• Activation of receptors can trigger the synthesis of small molecules called second messengers, which initiate and coordinate intracellular signaling pathways