CSB325 Lecture 6 Notes

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Cell and Systems Biology
David Lovejoy

CSB325 Lecture 6: Calcium Regulation Slide 2 Calcium regulation is closely related to osmoregulation. The calcium concentrations found in most organisms are similar to what is thought to be found in the waters of the prebiotic earth, so we’ve retained that. When I was talking about protocell evolution (early progenitors of cells that were forming their membrane), in some ways, the external environment was similar to the internal environment with respect to some ions. Calcium was one of those ions. Calcium has a number of very interesting attributes. It can play a role as a signalling molecule. It can play a role in structure. It can act to stabilize proteins. It is a key component of bone. Even though it is an ion, it is a mineral. It can act as a hormone in some cases. It acts as a secondary signaling molecule, an intracrine factor. Almost all of the hormones that we talk about in this course will regulate calcium at some point. Calcium is also responsible for the membrane integrity because it is carrying a positive charge. It can change the potential difference across the membrane. If calcium goes above or below its set point, a number of channels can open up, then the membrane can lose its integrity and it can kill the organism. It is essential that calcium is regulated inside of the cell, but also inside of the organism. We are going to talk primarily about organismal calcium regulation. This slide depicts two of the key hormones associated with calcium metabolism. In vertebrates, there are two basic hormone systems: calcitonin and parathyroid. Both of them act in tandem with each other and in opposition to each other to regulate the homeostasis of calcium. When calcium is too high, the thyroid gland releases calcitonin. Calcitonin is a peptide hormone. Calcitonin affects a number of cells to start regulating calcium, internalizing calcium, sequester calcium, and secrete calcium. As a result, calcium levels fall. Depending upon
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