Transduction Pathways
Biochemistry & Cell Biology > Cell Communication
Transduction pathways are cascades of molecular interactions Transduction pathways are cascades of molecular interactions Activation of receptors can trigger the synthesis of small molecules called second messengers, which initiate and coordinate intracellular signaling pathways.

Transduction pathways are cascades of molecular interaction relay signals from receptors to target molecules in the cell.

Transduction stage of cell signaling is usually a multi step pathway. Steps often include activation of proteins by addition or removal of phosphate groups, or release of other small molecules or ions that act as messengers. Signal amplification is one benefit of multiple steps. If some of the molecules in a pathway transmit the signal to numerous molecules at the next step in the series, the result can be a large number of activated molecules at the end of the pathway.

Series of biochemical reactions within the cell. Series of biochemical reactions within the cell. Activation of receptors can trigger the synthesis of small molecules called second messengers, which initiate and coordinate intracellular signaling pathways.

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. For example, cyclic AMP (cAMP) is a common second messenger involved in signal transduction cascades. (In fact, it was the first second messenger ever discovered.) cAMP is synthesized from ATP by the enzyme adenylyl cyclase, which resides in the cell membrane. The activation of adenylyl cyclase can result in the manufacture of hundreds or even thousands of cAMP molecules. These cAMP molecules activate the enzyme protein kinase A (PKA), which then phosphorylates multiple protein substrates by attaching phosphate groups to them. Each step in the cascade further amplifies the initial signal, and the phosphorylation reactions mediate both short- and long-term responses in the cell. cAMP can stop signaling by the enzyme phosphodiesterase.

Transduction pathways results in intricate cellular responses. Transduction pathways results in intricate cellular responses.

Other examples of second messengers include diacylglycerol (DAG) and inositol 1,4,5–triphosphate (IP3), which are both produced by the enzyme phospholipase, also a membrane protein. IP3 causes the release of Ca2+ – yet another second messenger – from intracellular stores.

Phosphorylation allows for intricate control of protein function. Phosphate groups can be added to multiple sites in a single protein, and a single protein may in turn be the substrate for multiple kinases and phosphatases.

At any one time, a cell is receiving and responding to numerous signals, and multiple signal transduction pathways are operating in its cytoplasm. Many points of intersection exist among these pathways. For instance, a single second messenger or protein kinase might play a role in more than one pathway. Through this network of signaling pathways, the cell is constantly integrating all the information it receives from its external environment.

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