Lactose

Definition

Lactose is a disaccharide sugar composed of glucose and galactose, primarily found in milk and dairy products. This sugar plays an essential role as an energy source for young mammals, but many individuals lack the enzyme lactase needed to digest it effectively, leading to lactose intolerance. Understanding lactose's structure and metabolism is crucial in the context of carbohydrates and prokaryotic gene regulation.

5 Must Know Facts For Your Next Test

1. Lactose accounts for about 2-8% of the weight of milk, providing a significant source of energy for infants.
2. In lactose-intolerant individuals, undigested lactose ferments in the gut, causing symptoms like bloating and diarrhea.
3. Prokaryotic cells can regulate the expression of lactase through operons, such as the lac operon in E. coli, which controls the metabolism of lactose based on its availability.
4. The ability to digest lactose beyond infancy is a result of genetic adaptation in some human populations, allowing them to exploit dairy resources.
5. Lactose can be utilized as a carbon source in fermentation processes by certain bacteria, making it important in food production, such as yogurt and cheese.

Review Questions

• How does the presence or absence of lactase affect an individual's ability to digest lactose?
  • The presence of lactase is essential for breaking down lactose into its component sugars, glucose and galactose, which can be absorbed by the body. Individuals with sufficient lactase levels can digest lactose without issue, while those with low or absent levels experience lactose intolerance. This condition leads to gastrointestinal discomfort due to the fermentation of undigested lactose by gut bacteria.
• Discuss how prokaryotic organisms regulate the metabolism of lactose through genetic mechanisms.
  • Prokaryotic organisms regulate lactose metabolism using systems like the lac operon found in E. coli. When lactose is present, it acts as an inducer that triggers the expression of genes responsible for its breakdown. The operon includes genes that code for proteins facilitating the uptake and digestion of lactose, allowing these organisms to adapt to available energy sources efficiently.
• Evaluate the evolutionary implications of lactase persistence in human populations and its relation to dietary practices.
  • Lactase persistence among certain human populations represents a significant example of gene-culture co-evolution. In societies where dairy farming became prevalent, individuals with mutations allowing continued lactase production into adulthood had a nutritional advantage. This led to higher survival rates and greater reproductive success, ultimately contributing to the spread of these genetic traits. As a result, areas with a history of dairy consumption often have higher frequencies of lactase persistence compared to regions where dairy was less integral to diet.

Related terms

Lactase: An enzyme produced by the small intestine that breaks down lactose into glucose and galactose, allowing for its absorption.

Monosaccharides:

The simplest form of carbohydrates, consisting of single sugar molecules like glucose and galactose that can combine to form disaccharides like lactose.

Operon:

A cluster of genes under the control of a single promoter, which can include genes involved in lactose metabolism in prokaryotic organisms.