DigestionNutritionCH50

DigestionNutritionCH50 - Nutrition, Digestion, and...

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Nutrition, Digestion, and Absorption
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Nutrient Requirements Animals are heterotrophs : They must obtain their nutrition by eating other organisms. Most plants, some bacteria, and some protists are autotrophs : They trap solar energy through photosynthesis and use that energy to synthesize all of their components. Heterotrophs depend on the organic synthesis carried out by autotrophs.
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Nutrient Requirements Most animals store fuel molecules that can be released as needed between meals. Carbohydrates are stored in liver and muscle cells as glycogen . The total glycogen store is about one day’s energy requirements. The most important form of stored energy in animals is fat. Fat has more energy per gram than glycogen, and it is stored with little associated water, making it more
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Nutrient Requirements Animals that do not take in enough food to meet their energy requirements are undernourished . They must metabolize molecules of their own body to provide the energy they need. The first storage compounds to be metabolized in this state are glycogen and fat, so that protein loss is minimized for as long as possible. Eventually, a starving animal must use its own proteins for fuel; the syndrome that results is called kwashiorkor . This impairs body functions and eventually leads to death.
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Figure 50.3 The Course of Starvation
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Nutrient Requirements All animals require certain basic organic molecules, called carbon skeletons , that they cannot synthesize themselves. An example is the acetyl group. Some carbon skeletons are derived from limited sources, and animals can suffer a deficiency of these materials even if their caloric intake is adequate. Amino acids are an example of carbon skeletons that can be in short supply.
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Figure 50.4 The Acetyl Group Is an Acquired Carbon Skeleton
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Nutrient Requirements Animals can synthesize some amino acids. Others must be acquired through food and are called essential amino acids ; they differ from species to species. There are eight essential amino acids for humans: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Most plant foods do not contain all eight amino acids, so vegetarians must eat a complementary mixture of foods (e.g., grains plus legumes) to obtain all eight.
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Figure 50.5 A Strategy for Vegetarians
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Nutrient Requirements Humans are able to synthesize almost all of their required lipids using acetyl groups obtained from food. Essential fatty acids such as linoleic acid must be obtained through a dietary source. Essential fatty acids are needed to make other fatty acids, components of signaling molecules, and membrane phospholipids.
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Nutrient Requirements The vitamins are another group of essential nutrients. Vitamins are carbon compounds that
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This note was uploaded on 04/02/2008 for the course BIO 188 taught by Professor Capco during the Fall '08 term at ASU.

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DigestionNutritionCH50 - Nutrition, Digestion, and...

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