LECTURE14DIGESTIVE_1

LECTURE14DIGESTIVE_1 - Februar y issue Digestive system Why...

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February issue Digestive system
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Why do we EAT???
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A nutritionally adequate diet satisfies three needs: fuel (chemical energy) for all the cellular work of the body; the organic raw materials animals use in biosynthesis (carbon skeletons to make many of their own organisc molecules); essential nutrients , substances that the animals cannot make for itself from any raw material and therefore must obtain in food in prefabricated form. Animals are heterotrophs that require food for fuel, carbon skeletons, and essential nutrients:
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ATP CARBOHYDRATES LIPIDS PROTEINS OXYDATION 1 st place 2 nd place 3 rd place Atkins diet???
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Digestion cleaves macromolecules into their component monomers, which the animal then uses to make its own molecules or as fuel for ATP production. Polysaccharides and disaccharides are split into simple sugars. Fats are digested to glycerol and fatty acids. Proteins are broken down into amino acids. Nucleic acids are cleaved into nucleotides.
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Nearly all ATP is derived from oxidation of organic fuel molecules - carbohydrates, proteins, and fats - in cellular respiration. The monomers of any of these substances can be used as fuel, though priority is usually given to carbohydrates and fats. Fats are especially rich in energy, liberating about twice the energy liberated from an equal amount of carbohydrate or protein during oxidation.
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When an animal takes in more calories than it needs to produce ATP, the excess can be used for biosynthesis. This biosynthesis can be used to grow in size or for reproduction, or can be stored in energy depots. In humans, the liver and muscle cells store energy as glycogen (long term source of stored energy), a polymer made up of many glucose units. Glucose is a major fuel molecule for cells THAT CAN BE USED IMMEDIATELY , and its metabolism, regulated by hormone action, is an important aspect of homeostasis. If glycogen stores are full and caloric intake still exceeds caloric expenditure, the excess is usually stored as fat.
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Besides fuel and carbon skeletons, an animal’s diet must also supply essential nutrients. These are materials that must be obtained in preassembled form because the animal’s cells cannot make them from any raw material. . For example, ascorbic acid (vitamin C) is an essential nutrient for humans and other primates, guinea pigs, and some birds and snakes, but not for most other animals (scurvy in sailors)
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An animal whose diet is missing one or more essential nutrients is said to be malnourished. For example, many herbivores living where soils and plants are deficient in phosphorus eat bones to obtain this essential nutrient.
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Animals require 20 amino acids to make proteins. Most animals can synthesize half of these
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LECTURE14DIGESTIVE_1 - Februar y issue Digestive system Why...

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