4.3: Signal Transduction

In topics 4.1 and 4.2, we got a grasp of the first two steps of signal transduction. We learned about the general concepts and specifics for reception and transduction. Topic 4.3 provides some more specific examples of signal response.

Vocab List

• Gene expression
  • Transcription factors
• Metabolic response
• Apoptosis
• Epinephrine (adrenaline)

Written Explanation

Signal Transduction Recap:

Examples of Signal Response:

Gene expression Many signal transduction pathways act as transcription factors. This means they regulate which parts of the DNA are read and synthesized into proteins. This may result in a change to the phenotype (observable characteristics) of the cell.	Diagram of gene expression as a result of signal transduction
Metabolic response This response takes place in the cytoplasm and affects the operation of proteins/enzymes. It can either stimulate or inhibit their activity.	Diagram of metabolic response as a result of signal transduction
Apoptosis Apoptosis is programmed cell death. It may be triggered by the immune system to prevent the spread of a disease.	Diagram of apoptosis

Examples of a pathway:

Epinephrine, also known as adrenaline, is a signaling molecule (ligand) that stimulates the breakdown of glucose.

1. Reception: Epinephrine is captured by a G-protein coupled receptor. Then, the bound G-protein is phosphorylated and released.
2. Transduction: The phosphorylated G-protein begins a transduction pathway that involves cyclic AMP (cAMP). This second messenger helps activate a phosphorylation cascade, amplifying and transmitting the signal.
3. Response: Eventually, glycogen phosphorylase converts glycogen into glucose and releases it from the liver, increasing blood sugar. This sugar is used in glycolysis to increase the body's energy, preparing it for a "fight or flight" situation.