Talks Aubrey de Grey
www.ted.com
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aging
Added: September 16, 2007, 1:29 pm
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The Cell Membrane
The cell membrane is a translucent pliable skin which controls the flow of materials into and out of the cell. A highly complex unit, it is composed of a double layer of fat molecules sandwiched between two layers of protein molecules. The exact molecular structure of the cell membrane is still unknown, but this diagrammatic model shows what is thought to be the relationship of carbohydrates with protein, water and fat molecules.
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membrane
Added: October 15, 2007, 8:04 pm
Runtime: 30.00 | Views: 12986 |
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Cell Equilibrium
Cell EquilibriumTo function properly the cell must maintain a stable internal environment; therefore, transfer of materials has to be achieved without an excessive buildup of chemicals. When particular molecules are needed-for example, glucose-the cell will take these in and discard other materials to preserve equilibrium. There are three types of transport when maintaining cell equilibrium. Passive transport occurs when chemicals concentrated outside the cell cause a flow of small molecules to push through the membrane until a balance exists. This process, known as diffusion, is the basis of the intake of digestive products by cells lining the intestines. Active transport is the process, using chemical energy, by which the cell takes in larger molecules that would otherwise be unable to enter in sufficient quantities. Carrier molecules within the cell membrane bind themselves to incoming molecules, rotate around them and release them into the cell. This is the means by which the cell absorbs glucose. Active transport may upset stability, but the cell compensates by shedding other matter. The movement of water through the cell membrane from areas of low to high chemical concentration is called osmosis. This alternative process provides for dilution of chemicals-unable to cross the membrane by diffusion-to maintain equilibrium within the cell.
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equilibrium
Added: October 15, 2007, 8:05 pm
Runtime: 87.67 | Views: 9389 |
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Chromosomes
ChromosomesChromosomes contain the genetic material deoxyribonucleic acid or DNA. In association with proteins, the twisted strands of DNA become coiled and folded to give chromosomes a beaded appearance. Each bead represents a gene-a length of DNA coding for the synthesis of one or more proteins. There are thought to be more than five hundred genes on each of the cell's forty-six chromosomes. Here a progression is shown from a chromosome, as it appears under the microscope, to the molecular architecture of DNA, shown diagrammatically to illustrate the double helix. The chromosome content of every cell in the body consists of forty-six individual chromosomes, except for the sperm and ova, which have only twenty-three. Highly magnified, this chromosome set shows the X (red) and the Y (blue) sex chromosomes. A combination of X and Y denotes male characteristics, while an XX pair results in the birth of a girl. Since sperm contain either X or the Y chromosome and the ova only the X, sex is governed by the sperm.
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chromosome
Added: October 15, 2007, 8:05 pm
Runtime: 74.00 | Views: 14731 |
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Skin: A Protective Coat
A Protective CoatSkin is like a tiered cake with a thin layer, the epidermis, on top and a thicker layer of connective tissue, the dermis, underneath. This is underlaid by subcutaneous tissue, containing fat cells. The epidermis itself is composed of a waterproof layer of flattened, dead cells, a thinner layer of non-dividing living cells and an innermost germinative layer of dividing cells. Just below this layer are the melanocytes, which produce the pigments that color skin. Embedded in the dermis are lymphatic vessels, nerve fibers and sensory nerve endings, blood capillaries, sweat glands and hair follicles. These follicles surround the shafts of hair and each has a lubricating sebaceous gland and a muscle which can erect the hair whenever body temperature falls
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skin
Added: October 15, 2007, 8:07 pm
Runtime: 52.00 | Views: 8019 |
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