Describe how cells communicate with each other using messenger molecules.

Cells communicate using chemical signals (often called ligands) which are proteins or other molecules, these move from the sending cell to the target cell. The target cell although must have the right receptor on the target cell to receive this message, when the signal binds to the it alters the shape of the receptor triggering a change (response of the message).

Cells and tissues release messenger molecules into their environments and often into the bloodstream. These messenger molecules have a very specific shape. The molecules travel to their target cell in the bloodstream or other transport system. When they reach their target cells, the messenger molecules may diffuse through the cell membrane if they are small and non-polar. This will cause a direct impact on the inside of the cell.

If the messenger molecule is large and/or polar, it will need to bind to a 'receptor' on the surface of the cell. Remember, the messenger has a specific shape. This is important because it needs to bind to a receptor which has a complementary shape to it, a bit like two pieces of a jigsaw puzzle fitting together. Once the messenger molecule and receptor bind to each other, the receptor changes shape. This causes a change inside the cell. This change depends on the specific messenger that binds to the specific receptor. For example, it could cause an increase in the number of specific proteins the cell produces (e.g. insulin). However, a different messenger may cause a decrease in the number of a specific protein produced by the cell.