Concept 41 2 minerals Chapter 41 There are four classes of essential nutrients essential amino acids essential fatty acids vitamins and Animals require 20 amino acids to make protein Most animals can synthesize half of these if their diet includes organic nitrogen The remaining essential amino acids must be obtained from food in prefabricated form Eight amino acids are essential in the adult human with a ninth histidine being essential for infants The same amino acids are essential for most animals A diet that provides insufficient amounts of one or more essential amino acids causes a form of malnutrition known as protein deficiency This is the most common type of malnutrition among humans The victims are usually children who if they survive infancy are likely to be retarded in physical and Because the body cannot easily store amino acids a diet with all essential amino acids must be eaten perhaps mental development each day or protein synthesis is retarded Some animals have special adaptations that get them through periods where their bodies demand extraordinary amounts of protein For example penguins use muscle proteins as a source of amino acids to make new proteins during molting While animals can synthesize most of the fatty acids they need they cannot synthesize essential fatty acids These are certain unsaturated fatty acids including linoleic acids which are required by humans Most diets furnish ample quantities of essential fatty acids and thus deficiencies are rare Vitamins are organic molecules required in the diet in quantities that are quite small compared with the relatively large quantities of essential amino acids and fatty acids animals need While vitamins are required in tiny amounts from about 0 01 mg to 100 mg per day depending on the vitamin vitamin deficiency or overdose in some cases can cause serious problems So far 13 vitamins essential to humans have been identified These can be grouped into water soluble vitamins and fat soluble vitamins with extremely diverse The water soluble vitamins include the B complex which consists of several compounds that function physiological functions as coenzymes in key metabolic processes Vitamin C also water soluble is required for the production of connective tissue Excessive amounts of water soluble vitamins are excreted in urine and moderate overdoses are probably harmless The fat soluble vitamins are A D E and K They have a wide variety of functions Vitamin A is incorporated in the visual pigments of the eye Vitamin D aids in calcium absorption and bone formation Vitamin E seems to protect membrane phospholipids from oxidation Vitamin K is required for blood clotting Excess amounts of fat soluble vitamins are not excreted but are deposited in body fat Overconsumption may lead to toxic accumulations of these compounds The subject of vitamin dosage has aroused heated scientific and popular debate Some believe that it is sufficient to meet recommended daily allowances RDAs the nutrient intake proposed by nutritionists to maintain health Others argue that RDAs are set too low for some vitamins and a fraction of these people believe probably mistakenly that massive doses of vitamins confer health benefits Debate centers on the optimal doses of vitamins C and E While research is ongoing all that can be said with any certainty is that people who eat a balanced diet are not likely to develop symptoms of vitamin deficiency Minerals are simple inorganic nutrients usually required in small amounts from less than 1 mg to effects damage Concept 41 3 about 2 500 mg per day Mineral requirements vary with animal species Humans and other vertebrates require relatively large quantities of calcium and phosphorus for the construction and maintenance of bone Calcium is also necessary for the normal functioning of nerves and muscles Phosphorus is a component of the cytochromes that function in cellular respiration Iron is a component of the cytochromes that function in cellular respiration and of hemoglobin the oxygen binding protein of red blood cells Magnesium iron zinc copper manganese selenium and molybdenum are cofactors built into the structure of certain enzymes Magnesium for example is present in enzymes that split ATP Sodium potassium and chloride are important in nerve function and have a major influence on the Iodine is required for thyroid hormones which regulate metabolic rate osmotic balance between cells and the interstitial fluids Excess consumption of salt sodium chloride is harmful The average U S citizen eats enough salt to provide about 20 times the required amount of sodium Excess consumption of salt or several other minerals can upset homeostatic balance and cause toxic side For example too much sodium is associated with high blood pressure and excess iron causes liver Ingestion the act of eating is only the first stage of food processing Food is packaged in bulk form and contains very complex arrays of molecules including large polymers and various substances that may be difficult to process or even toxic Animals cannot use macromolecules like proteins fats and carbohydrates in the form of starch or other polysaccharides First polymers are too large to pass through membranes and enter the cells of the animal Second the macromolecules that make up an animal are not identical to those of its food For example soybeans fruit flies and humans all assemble their proteins from the same 20 amino acids Digestion the second stage of food processing is the process of breaking food down into molecules In building their macromolecules however all organisms use common monomers small enough for the body to absorb 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 Digestion reverses the process that a cell uses to link together monomers to form macromolecules Rather than removing a molecule of water for each new covalent bond formed digestion breaks bonds with the addition of water via enzymatic hydrolysis A variety of hydrolytic enzymes catalyze the digestion of each of the classes of macromolecules found Chemical digestion is usually preceded by mechanical fragmentation of the food by chewing for Breaking food into smaller pieces increases the
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