lactose

(noun)

the disaccharide sugar of milk and dairy products, C12H22O11, (a product of glucose and galactose) used as a food and in medicinal compounds.

Related Terms

  • lactose intolerance
  • lactase

Examples of lactose in the following topics:

  • Lactose Intolerance

    • Lactose intolerance is the inability to digest lactose, a sugar found in milk, due to a lack of the enzyme lactase.
    • Lactose intolerant individuals have insufficient levels of lactase, the enzyme that metabolizes lactose into glucose and galactose, in their digestive system .
    • However, those living among societies that are largely lactose-tolerant may find lactose intolerance troublesome.
    • About 44% of lactose intolerant women regain the ability to digest lactose during pregnancy.
    • Individuals who suffer from lactose intolerance have insufficient levels of lactase to break down the lactose in milk and dairy products.
  • The lac Operon: An Inducer Operon

    • The lac operon is an inducible operon that utilizes lactose as an energy source and is activated when glucose is low and lactose is present.
    • One such sugar source is lactose.
    • Only lacZ and lacY appear to be necessary for lactose catabolism.
    • Second, lactose must be present.
    • The cell can use lactose as an energy source by producing the enzyme b-galactosidase to digest that lactose into glucose and galactose.
  • Galactosemia and Glycogen Storage Disease

    • Although the sugar and lactose metabolizes to galactose, galactosemia is not related to and should not be confused with lactose intolerance.
    • Lactose in food (such as dairy products) is broken down by the enzyme lactase into glucose and galactose.
    • The only treatment for classic galactosemia is eliminating lactose and galactose from the diet.
    • Infants with classic galactosemia cannot be breast-fed due to lactose in human breast milk and are usually fed a soy-based formula.
    • Galactosemia is sometimes confused with lactose intolerance, but galactosemia is a more serious condition.
  • Detecting Acid and Gas Production

    • Traditionally, MacConkey agar has been used to distinguish those bacteria that ferment lactose from those that do not.
    • Gut bacteria, such as Escherichia coli, can typically ferment lactose; important gut pathogens including Salmonella enterica and most shigellas are unable to ferment lactose.
    • Shigella sonnei can ferment lactose, but only after prolonged incubation; it is referred to as a late-lactose fermenter.
    • Those bacteria unable to ferment lactose, often referred to as nonlactose fermenters (NLFs) metabolize the peptone in the medium.
    • In sorbitol MacConkey agar, lactose is replaced by sorbitol.
  • Disaccharides

    • Lactose, also known as milk sugar, is a galactose-glucose compound joined as a beta-glycoside.
    • Many adults, particularly those from regions where milk is not a dietary staple, have a metabolic intolerance for lactose.
    • Infants have a digestive enzyme which cleaves the beta-glycoside bond in lactose, but production of this enzyme stops with weaning.
    • Cheese is less subject to the lactose intolerance problem, since most of the lactose is removed with the whey.
  • Catabolite Activator Protein (CAP): An Activator Regulator

    • This type of process can be seen in the lac operon which is turned on in the presence of lactose and absence of glucose.
    • This opens up the DNA molecule, allowing RNA polymerase to bind and transcribe the genes involved in lactose catabolism.
    • As cAMP-CAP is required for transcription of the lac operon, this requirement reflects the greater simplicity with which glucose may be metabolized in comparison to lactose.
  • Chemical Digestion of Carbohydrates, Proteins, Lipids, and Nucleic Acids

    • Lactase is an enzyme that breaks down the disaccharide lactose into its component parts, glucose and galactose, which can also be absorbed by the small intestine.
    • This condition is commonly known as lactose intolerance.
  • Malabsorption of Nutrients

    • Researchers then discovered that lactose malabsorption is actually the norm for most populations in the world.
    • Lactase deficiency, which prevents the breakdown of lactose, is a common cause of malabsorption.
    • For example, patients may be put on a gluten-free diet for celiac disease or taught lactose avoidance for lactose intolerance.
  • Culture and Biology

    • For instance, prior to about 4000 BCE, most humans did not produce a protein that allowed them to digest lactose after being weaned.
    • After Europeans began to drink the milk of domesticated animals, the genetic adaptation favoring lactose consumptions spread rapidly throughout the continent.
    • This is an example in which cultural shifts (the domestication of animals) can lead to changes in behavior that affect biology (genetic adaptation to process lactose).
    • People began domesticating cattle many years before they developed the genes for lactose tolerance.
  • Selective and Differential Media

    • Streptococcuseosin methylene blue (EMB), which is differential for lactose and sucrose fermentation.
    • MacConkey (MCK), which is differential for lactose fermentationmannitol salt agar (MSA), which is differential for mannitol fermentation.
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