Signal Transduction

Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm. Continuation of a signal in this manner is called signal transduction. Signal transduction only occurs with cell-surface receptors because internal receptors are able to interact directly with DNA in the nucleus to initiate protein synthesis (Figure 1).

From the top, a sphere named ‘Extracellular Signal Molecule’ is attached to a chalice-like structure named ‘Receptor Protein’, which lower part is embedded inside a horizontal, slightly bent line called ‘plasma membrane of the target cell’. From the bottom of the chalice-like structure, three arrow point down to a square, a triangle and a circle, which are the second messengers. Each second messenger enters the cell nucleus and interacts with a semicircle-like structure, a transcription regulatory protein. These last molecule will alter gene expression, represented as a double helix.

Figure 1: Signal transduction cascade Following binding of the ligand to its matching receptor on the cell surface, the signal is transmitted to the inside of the cell and propagated by second messengers. These, in turn, activate effector proteins (such as transcription factors) that induce a change in gene expression of the cell.

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