Essential Knowledge 3.D.3

Signal transduction pathways link signal reception with cellular response.

Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein. Different receptors recognize different chemical messengers, which can be peptides, small chemicals or proteins, in a specific one-to-one relationship. A receptor protein recognizes signal molecules, causing the receptor protein’s shape to change, which initiates transduction of the signal. Examples include:

• G-protein linked receptors
• Ligand-gated ion channels
• Receptor tyrosine kinases

NOTE: No particular system is required for teaching the concepts above. Teachers are free to choose a system that best fosters student understanding.

Signal transduction is the process by which a signal is converted to a cellular response. Signaling cascades relay signals from receptors to cell targets, often amplifying the incoming signals, with the result of appropriate responses by the cell. Second messengers are often essential to the function of the cascade. Examples include:

• Ligand-gated ion channels
• Second messengers, such as cyclic GMP, cyclic AMP calcium ions (Ca²⁺), and inositol triphosphate (IP₃)

Many signal transduction pathways include:

• Protein modifications (an illustrative example could be how methylation changes the signaling process)
• Phosphorylation cascades in which a series of protein kinases add a phosphate group to the next protein in the cascade sequence

Students should be able to:

LO 3.36 Describe a model that expresses the key elements of signal transduction pathways by which a signal is converted to a cellular response.