Lactose present in milk is a?

BHU NO - 2015

Biochemistry & Nutrition

Easy

Appeared in: BHU NO - 2015

Explanation

Lactose, the primary sugar in milk, is classified as a disaccharide.
A disaccharide is a carbohydrate formed when two simple sugars (monosaccharides) are joined by a glycosidic bond.
Lactose is specifically composed of one molecule of glucose and one molecule of galactose.
Upon digestion by the enzyme lactase, it breaks down into these two monosaccharide units for absorption.

Option A: Polysaccharides are complex carbohydrates made of many (typically more than ten) monosaccharide units linked together. Lactose is composed of only two units.
Option C: While lactose is made of two different monosaccharides, the term 'heteropolysaccharide' is used for very large polymers containing different types of repeating monosaccharide units, such as hyaluronic acid. 'Disaccharide' is the correct and more specific classification for a two-unit sugar.
Option D: Monosaccharides are the simplest form of carbohydrates, consisting of a single sugar unit. Lactose can be broken down (hydrolyzed) into two monosaccharides (glucose and galactose).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Biochemical classification of carbohydrates as background academic context rather than a clinical decision trigger.
Understanding that lactose is a disaccharide is fundamental to comprehending lactose intolerance, a common clinical condition where the body lacks the enzyme lactase needed to break the bond between glucose and galactose.
Nurses play a key role in educating patients with lactose intolerance about dietary modifications, such as avoiding dairy products or using lactase supplements, to manage symptoms like bloating, gas, and diarrhea.
What if? If a patient is an infant presenting with persistent diarrhea and failure to thrive, the nurse should consider the possibility of congenital lactase deficiency, a rare but serious condition requiring a specialized lactose-free formula for proper nutrition and growth.

How to Approach the Question

First, identify the key term in the question: 'Lactose'.
Recall the basic classification of carbohydrates based on the number of sugar units: mono- (one), di- (two), and poly- (many).
Associate lactose with its common source, which is milk sugar.
Remember or deduce that lactose is formed from two simpler sugars, glucose and galactose.
The prefix 'di-' means two, so a sugar made of two units is a 'disaccharide'.
Compare this with the other options: Polysaccharides are long chains (like starch), and monosaccharides are single units (like glucose), making them incorrect choices.

Concept Tested & Keywords

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E6 textbook of Applied Biochemistry and Nutrition & DieteticsHarbans Lal (pp 26-464 of 479) p. 16-18

E6 Nutrition Monika Sharma 3e p. 63-65

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 76-78