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Lecture 1 – June 7, 2011We have many feedback mechanisms that allow us to adjust to changes in our internal and external environment and maintain homeostasis.Negative Feedback MechanismsNegative feedback mechanisms digress from standard and goes back to standard.Right side of diagram - If you have a snack of a Dr. Pepper and a Snickers, your glucose level will increase (Average level of glucose in plasma of blood is 90 mg / 100 ml of blood). We are starting to digress from the standard. The Beta Cells of the Islets of Langerhans in the Pancreas is designed to detect movement of glucose level away from the 90 mg mark. The hormone insulin is the first messenger and is looking for a target cell receptor. The target cell then absorbs glucose from blood plasma. The bottom line is that the target cell’s job is to solve the problem. The problem is that we have too much glucose, therefore the glucose goes into the target cell (by a series of steps). Glucose is the molecule that a cell depends on for energy and is used via cellular respiration. To get the glucose in and out of cell requires a method of transport. Glucose will only get into the cell if insulin allows it to.Left side of diagram – Later in the day, you have not eaten anything. Glucose level is supposed to be 90 mg / 100 ml of blood, but it is lower instead (so you would go left on the diagram). The sensor that senses that your glucose level is decreasing is the Alpha Cells of the Islets of Langerhans in the Pancreas. The Alpha Cells release the hormone glucagon, which looks for a target cell. Glucagon attaches to the receptor and glucose is kicked out of the cell, to help raise the glucose level, thus returning to the standard.Other examples of negative feedback include maintaining calcium levels. If you have too much calcium, thyrocalcitonin is released to bring the level down. If you do not have enough calcium, parathormone is released to bring the level up.If homeostatic mechanisms do not work properly, or you interrupt positive or negative feedback, you can get disease.If glucose is not going into the cell, fat will go into the cell and cause ketosis, which can lead to atherosclerosis, high blood pressure, and cardiovascular disease. The top cause of death in diabetics is cardiovascular disorders because their bodies constantly burn fat.Positive Feedback MechanismsPositive feedback does not occur as much as negative feedback. An example of positive feedback is childbirth.During childbirth: As the baby grows and positions itself and gets closer to coming out, the uterus gets more receptors (pressure receptors). These pressure receptors go up to the mom’s brain and say that it is time to release oxytocin. Oxytocin goes “down” the body and starts to make things move down, to get ready for birth. More pressure, more oxytocin. More pressure, more oxytocin, etc. Then childbirth occurs.Most positive feedback mechanisms lead to something of a more disastrous nature. It constantly moves away from the standard. If the actual childbirth did not occur, the mother would die because you keep moving from the standard, no going back to it. Other examples of positive feedback include cancer and blood clots.The Cell & Cellular Membrane (Chapter 3)The cell is the basic unit of structure and function that carries out the activities of life. Cells on the outside of your skin have to be really close together so nothing comes out of your body. Desmosomes (tight junctions) make the skin cells stay close together. Gap junctions have a connection so that ions can travel between cells.The cell membrane is an organelle. Its number one responsibility is to control what goes in and what comes out. When the cell membrane can no longer do this, we say it is losing its integrity and it is on its way to death. One of the first signs of a cell dying is shrinking (crenation) or if it’s poofy (lysis). Transport – how things get in and out of the cell membrane.The cell membrane is a double phospholipid membrane. Out of the cell – extracellular, intercellular, interstitial. Double phospholipid layer is composed of two phosphates and two lipids. Phosphates like water (hydrophilic), while the lipids do not like water (hydrophobic).Basic unit of a protein is amino acids. There are 20 amino acids. They are connected together by peptide bonds. Integral proteins are proteins that go from the outside to the inside, through the membrane itself. Integral means all the way through. There will be some proteins that will be on the outside or stuck on the inside and they are called peripheral proteins. Three important integral proteins are 1) stretches and forms a tube or channel or passageway from the outside to the inside, or from the inside to the outside. 2) Makes up things such as the pumper molecule (this integral protein is represented as an X). 3) Enzymes and other kinds of molecules (represented as curly q’s). Always think of a protein as the brain of the cell because they are functional and make things happen. The phospholipid is structural. Sometimes peripheral proteins have the job of opening or closing the channels. Sometimes they turn on/off enzymes. Enzymes decrease the level of activation energy required and speed up the reaction.Lecture 2 – June 8, 2011Cellular MembraneIt is up to the cell membrane to decide what ions go in and out of the cell.What is the chemical part of the cell membrane that is important for structure? The double phospholipid layer.Proteins are the brains of the cell membrane.Three types of integral proteins: 1) channels or pores 2) pumper molecules 3) enzymesAttached to the inside (or outside) of the cell are peripheral proteins. Some might be opening and closing the channels (we call this “acting like gates”), they sometimes might turn on an enzyme, or they might be there to act as a receptor.The most repeated unit in the membrane is the phospholipid.There are good and bad types of cholesterol. The cholesterol on the edges of the cell membrane support it and also help the membrane maintain a certain level of rigidity but yet fluidity. We want some cholesterol in our body to keep the membrane stable so it doesn’t just float off.Cellular Membrane – PolarityThe cell membrane must be polarized in order for it to function properly. When a membrane of a cell is at rest (not letting things go in and out of the cell), we call that a resting membrane. The resting membrane has a charge difference and it is said

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UL Lafayette BIOL 220 - Exam 1 Notes

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