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Lecture 21.docx

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Biological Sciences
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Dan Riggs

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Lecture 21 - Signal transduction I We will talk about the general signaling pathway and about some early experiments that started the signaling research going. This starts in chapter 15. Cellular communication and signal transduction are what we are going to talk about for the next couple of lectors. There are three basic strategies that multicellular organisms use to respond to extracellular signaling molecules. The first one is “self” and in figure 15 – 1, you see in the first panel something called an autocrine signal. Auto means self so what happens is that the cell in the middle is making some type of signaling molecule that is secreting from the cell and it's in the local environment but the cell itself that made the signal is now receiving the signal at a receptor at its cell surface. This is important for a variety of cell regulations. The second mechanism is known as “local” signaling and the technical name is paracrine signaling. In this case there is the cell in the middle that is making signaling molecules in yellow and in this case it affects its neighbors in the nearby vicinity through diffusion are receiving the signal and setting in motion a set of events to respond to the signal. Lastly, there is a way for multicellular organisms as a “systemic” way to signal. Endocrine glands make signals like hormones and they send those hormones into the circulatory system where they can be unloaded at very distant sites to control cells that are in fact very far away. Figure 15 – 2 looks complicated but is not. Basically know the notes that are on the right side of the slide. At the top is a signaling cell which has made a signal for example a hormone. The cell membrane is shown in blue and you see some transmembrane receptors that are present. The response of the second cell can only take place if that cell can see the signal. That is, if it has a receptor that binds to that particular signal then something is going to happen. If it cannot detect the signal that is if it doesn't have the receptor, then it obviously will not direct the response. This is important. There are two types of response pathways one on the left and one on the right. Simplistically they could be said to be with or without that effector molecule. This takes place inside the plasma membrane where the receptor becomes activated. Usually, there are several steps which can be branch pathways, pathways inactivating other pathways, and depending on the response pathway, the results can vary dramatically. For example, for a specific type of stimulus, it might cause some of the muscle cells to contract where as it would cause other muscle cells like your heart or lungs to relax so that you can get more oxygen so the heart to beat faster etc to allow you to respond to some stimulus. As you see at the bottom of figure 15 – 2 the outcomes are quite variable. It can be a simple metabolic change, it can be cell death, the cell might move or cause translation, which may improve its survival, transcription may be altered the cytoskeleton may be altered, or some combination of these things to eventually arrive at a response. Hormones are chemical substances that are produced in certain glands called endocrine glands. These are delivered to the circulatory system that distributes these signals to all cells of the organism. Some cells respond but some cells don't depending on whether or not they have the receptors for this hormone. For the rest of the lecture we will talk about two historical experiments. First one took place in early 1800s by a man named Arnold Berthhold who was interested in the role of the testes in male sexual development. The second experiment is a Canadian connection from two Canadian scientist Bayliss and Starling about the early 1900s who were interested in the role of the circulatory system versus the nervous system in delivering signaling molecules. Let's start with the Berthold experiment. He was interested in the role of testes in male sexual development. In the early 1800s, there was no molecular biology. When you went to go see a doctor, the doctor was a barber surgeon and if you had something wrong with you, quite often the doctor would slit your wrist and let you bleed which was
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