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Lactose Intolerance
Lactose is a disaccharide that is found in milk and dairy products such as cheese, sour cream, yogurt, ice cream, etc. When we ingest this sugar and it makes its way into our small intense, our cells begin to release a digestive enzyme called lactase. Lactase cleaves the beta-1,4 glycosidic bond in lactose and produces two monosaccharides, namely glucose and galactose. The two individual monosaccharides can now be ingested into the cells of the body and broken down for ATP molecules. In some individuals who have lactose intolerance, also known as hypolactasia, the lactase enzyme loses its efficiency to break down the lactose disaccharide. When they ingest the lactose, it begins to build up in the lumen of the small intestine and this can lead to problems such as gastrointestinal discomfort (pressure and swelling), flatulence, digestive problems (inability to absorb nutrients such as proteins and lipids) and diarrhea. These problems are a result of the 100 trillion bacterial cells that are found in our gut. These bacterial cells break down the lactose via lactic acid fermentation, which increases the concentration of lactate in the lumen of the gut. This creates a hypertonic environment and that causes water to flow into the lumen, leading to a watery stool (diarrhea). In addition, the bacterial cells also produce and release methane and hydrogen gas, which can lead to pressure build up. The combined effects of the gas buildup and diarrhea can decrease the ability of the gut to absorb nutrients. A much more severe version of lactose intolerance is classic galactosemia. This is characterized by the inability to break down galactose monosaccharides. These individuals can break down lactose into glucose and galactose but they cannot actually digest the galactose any further. Since the lactose breakdown leads to an increased concentration of galactose, this is also a form of lactose intolerance. This condition is a result of a mutation in the gene that codes for an enzyme called galactose 1-phosphate uridyl transferase, which is an enzyme used in the galactose-glucose interconversion pathway. In an individual with classic galactosemia, both of the genes on the homologous chromosome pair are mutated or missing (autosomal recessive disease). Although the cell can transform the galactose into galactose 1-phosphate, the interconversion pathway cannot go on any further. Therefore, there is a build up of galactose and galactose 1-phosphate. In addition, as the galactose concentration increases, an enzyme called aldose reductase begins transforming the galactose into galactitol. When the concentration of galactitol increases inside the cell, it can create a hypertonic environment that can cause the cells to swell with water. This can lead to many problems, including cataracts (water moves into the cells of the lens), liver enlargement and cirrhosis, jaundice, ovarian failure, lethargy and delayed mental development.
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