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Structural View of Biology

Infrastructure and Communication Cells require a complex infrastructure of molecules for support and communication. Our bodies contain about 10 trillion cells, which must cooperate for the good of the entire body. This requires a complex infrastructure to organize them into tissues and organs, and a complex network of signals to coordinate their action.

Hormones are used to communicate over long distances throughout the body. A hormone is made in one location in the body and dropped into the bloodstream. It then travels to a distant location and is received by receptors on the cell surface.

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  • Anabolic Steroids

    Anabolic Steroids

    Athletes are constantly striving for better performance in their sports. Most athletes stay in top shape through a rigorous training program in fitness and nutrition, giving them the strength and stamina to push their bodies to the physical limit. But some athletes also look to biochemistry to improve their performance even further. There are many ways to give nature an artificial boost. For instance, some athletes artificially increase the number of red blood cells in their blood, either by injecting purified cells or by using the blood-stimulating hormone erythropoietin. The extra red blood cells carry more oxygen to their straining muscles than in normal blood, giving them an edge in endurance. Similarly, many male athletes use steroid hormones like testosterone to spur their muscles into growth far beyond what is normally possible, giving them the edge in strength. These methods are controversial and regarded by many to be unethical, and thus are generally banned from organized sporting events. However, the many drug testing scandals currently in the news show that these methods are still in widespread use.

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  • Estrogen Receptor

    Estrogen Receptor

    Estrogens are small, carbon-rich molecules built from cholesterol. This is quite different than larger hormones, such as insulin and growth hormone, which are sensed by receptors on the cell surface. Estrogens pass directly into cells throughout the body, so the cell can use receptors that are in the nucleus, right at the site of action on the DNA. When estrogen enters the nucleus, it binds to the estrogen receptor, causing it to pair up and form a dimer. This dimer then binds to several dozen specific sites in the DNA, strategically placed next to the genes that need to be activated. Then, the DNA-bound receptor activates the DNA-reading machinery and starts the production of messenger RNA.

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  • Glucagon


    Too much glucose in the blood can lead to serious problems like diabetes, but too little glucose will also cause problems, starving cells throughout the body. Your body uses two main hormones, secreted by cells in the pancreas, to get the balance just right. Just after we eat, insulin is released, telling cells to take glucose out of the blood and store it for future use. Between meals, glucagon is released and has the opposite action, telling these same cells to release glucose for use in energy production and metabolism.

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    Discussed Structures
  • Growth Hormone

    Growth Hormone

    As children grow, their height, weight and strength increase. Numerous factors influence this growth, including the genetic makeup of the child, nutrition and environmental factors. Specific messengers released by the body also stimulate and regulate growth. Growth hormone is one key growth signal released from the pituitary, a pea-sized gland located at the base of the brain. Lack of this hormone in children can cause them to remain shorter than average, while in its excess they may grow taller than most. Growth hormone continues its work in adults, playing an important role in repair and maintenance of different tissues in the body.

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  • Insulin


    Our cells communicate using a molecular postal system: the blood is the postal service and hormones are the letters. Insulin is one of the most important hormones, carrying messages that describe the amount of sugar that is available from moment to moment in the blood. Insulin is made in the pancreas and added to the blood after meals when sugar levels are high. This signal then spreads throughout the body, to the liver, muscles and fat cells. Insulin tells these organs to take glucose out of the blood and store it, in the form of glycogen or fat.

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    Discussed Structures
  • Insulin Receptor

    Insulin Receptor

    Cells throughout the body are fueled largely by glucose that is delivered through the bloodstream. A complex signaling system is used to control the process, ensuring that glucose is delivered when needed and stored when there is a surplus. Two hormones, insulin and glucagon, are at the center of this signaling system. When blood glucose levels drop, alpha cells in the pancreas release glucagon, which then stimulates liver cells to release glucose into the circulation. When blood glucose levels rise, on the other hand, beta cells in the pancreas release insulin, which promotes uptake of glucose for metabolism and storage. Both hormones are small proteins that are recognized by receptors on the surface of cells.

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  • Leptin


    The delivery of nutrients to cells throughout the body is controlled by a complex network of signaling molecules. Some of these signals happen without us really noticing, for instance, when insulin and glucagon control the level of glucose that is delivered through the blood after we eat. The signaling protein leptin, however, has a more apparent effect, acting within the system that makes us hungry when we need food.

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  • Vitamin D Receptor

    Vitamin D Receptor

    Vitamins are exotic molecules that are essential for the proper function of cells, but somewhere along the process of evolution, our bodies have lost the ability to make them. So instead, we need to obtain them in our diet, or in a daily multivitamin tablet. These include vitamin A, which is used to build the light sensors in our eyes, a host of B vitamins used to build specialized tools for chemical reactions, and vitamin C, which plays an essential role in construction of collagen. Vitamin D is an exceptional case: our cells can make it, but only if there is enough sunlight.

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  • cAMP-dependent Protein Kinase (PKA)

    cAMP-dependent Protein Kinase (PKA)

    Phosphate groups are perfect chemical groups for modifying the function of proteins: they have a strong negative charge, they are fairly bulky, and they can form multiple hydrogen bonds. When a phosphate group is attached or removed to a protein, it may modify the shape and flexibility of the protein chain, or provide a readily-visible handle for recognition by other proteins. Cells take full advantage of these possibilities, and in a typical cell, phosphate groups are used to regulate the function of about one third of their proteins.

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