Lactose is the chemical name for milk sugar--it occurs naturally in milk and other dairy products. While your cells can use the chemical building blocks of lactose as a source of chemical energy, lactose doesn't have any special biological importance to humans--you can just as easily obtain nutrition from other carbohydrates.
Lactose
The lactose molecule bears some resemblance to the sucrose molecule, which goes by the common name table sugar. Like sucrose, lactose is a disaccharide, meaning it's made up of two smaller sugar units. These units, named glucose and galactose, serve as sources of chemical energy for your cells. Your cells depend upon small sugar units, particularly glucose, for energy, but there are many sources of glucose aside from lactose--starch and table sugar are examples, explains Dr. Lauralee Sherwood in her book "Human Physiology."
Special Significance
To most humans, lactose has no special significance. While you can digest lactose and use the compounds for energy, there's no particular benefit to lactose as an energy source. To some individuals, however, lactose does have biological importance. If you're lactose intolerant, you don't produce the enzyme that digests lactose in the food you eat. This leads you to experience significant intestinal discomfort upon lactose consumption, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Significance to Bacteria
Lactose is a potential food source for multiple bacterial species. Humans use the lactose-digesting properties of certain non-pathogenic--meaning non-infective--bacteria to manufacture food products. Bacterial species like Lactobacillus acidophilus can digest the lactose in milk, producing lactic acid. The lactic acid then reacts with proteins in the milk, leading to development of a creamy texture. The acid also adds a sour flavor to the milk. Together, these changes turn milk into yogurt.
Other Considerations
One of the important features of lactose from a biologist's point of view is that it triggers production of a set of genes in some bacteria. Many bacteria don't possess the ability to digest lactose all the time--instead, they can only digest lactose when there's lactose present in the environment and when other food sources are scarce. This observation by biologists opened up a field of research on genetic features called "operons," which control DNA and protein production. Lactose, which triggers the "lac operon," is one of the best-studied operon activators.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
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