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4.2 Introduction to Signal Transduction





⏱️  3 min read

written by

Annika Tekumulla

annika tekumulla

Transduction is the conversion of a signal into a cellular response. Transduction occurs in one step but the majority of the time it takes multiple changes.

These multiple steps are called the signal transduction pathway. The signal transduction pathway is when a small collection of signal molecules produce a large response across the cell. The large response across the cell is called the cascade effect. The response of a cascade can be cell growth, gene expression, or secretion of molecules.

Memory Tip: A good way to think about the signal transduction pathway is like a waterfall or a line of falling dominoes.


Image courtesy of Giphy.

Regardless of the distance between the cells, cell communication always follows the same 3 steps: reception, transduction, and response. 

Reception occurs when the signal (can be a chemical, peptide, or protein) is detected when the ligand (signaling molecule) binds to the receptor protein in a target cell. This causes a change in the shape of the cytoplasm of the inside of the receptor. Then, transduction occurs. In transduction, the signal is transmitted through the cell and is amplified. Finally, the third step is the response. The response is when the signal is carried out. An example of a response is when the cell activates RNA polymerase which leads to the transcription of a gene.


Image courtesy of Winnacunnet Biology.

Cell Surface Receptors

Cell surface receptors are receptors that cover the entire membrane. These receptors are important because most signaling molecules are too big to cross the plasma membrane. 

The plasma membrane contains a phospholipid bilayer. The heads of the phospholipid are “water-loving” which are called hydrophilic. The tails of the phospholipid are “water-hating” which are called hydrophobic.

The phospholipid bilayer is very important because it creates a barrier between the inside and outside of the cell.

Examples of cell surface receptors

Ion Channel Receptors involves a channel that opens and closes. The channel is used to allow the passage of ions across the membrane.

Memory Tip: Think of ion channel receptors as a toll booth. Just like a channel receptor, a toll both opens and closes after an action is made.

G-Protein-Coupled Receptors: Through this process, the ligand binds to the outside part of the cell and changes the form of the inside cytoplasm. This causes a G protein to bind and activate the enzyme adenylyl cyclase. Adenylyl cyclase converts ATP (energy) to cyclic-AMP.

Finally, cyclic-AMP activates other molecules inside the cell which finally leads to the cellular response.

Transduction has a link to evolution

Since transduction occurs in an animal, bacterial, plant, and yeast cells, it shows that the signal transduction pathway has evolved from a common ancestor.

Isn’t it crazy that all these different organisms could have something in common?!


Image courtesy of Giphy.

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