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Upregulation and downregulation
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A cell's response to a chemical signal, such as a hormone, not only depends on the presence of the correct receptor, but also on the number of receptors present. The more receptors a cell has for a specific signalling molecule, the greater the cellular response. The increase in a cell's response to a stimulus is called upregulation, whereas a reduced response to a stimulus is called downregulation.
Upregulation over time
Upregulation increases a cell's sensitivity to a specific hormone. It can occur by production of more receptors, or by decreasing the rate at which existing receptors are broken down. Upregulation generally occurs when the concentration of a signal molecule is very low. An increased number of receptors increases the chances of interacting with the signal to bring about a response. Example: During the last trimester of pregnancy there is an increase in uterine oxytocin receptors. Binding of oxytocin induces uterine contraction during labour helping to expel the fetus.
Downregulation over time
Downregulation decreases a cell's sensitivity to a signal molecule. Receptor numbers are decreased by reducing the production of receptor proteins or increasing the rate at which existing receptors are broken down. This reduces the receptors available to interact with the signal molecule. Downregulation protects against receptor over-stimulation. It generally occurs when the levels of a signal molecule are very high or when there has been long term exposure to a particular signal molecule. Example: Prolonged high blood glucose decreases insulin production in people with type 2 diabetes (insulin resistance).
1. Explain the purpose of cell signalling:
2. Identify the components shared by all types of communication involving chemical signalling:
3. (a) How can a cell alter its response to a signal molecule?
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(b) Use examples to contrast upregulation and downregulation and explain why these mechanisms are important:
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