Lecithin on hydrolysis yields all the following except?

Appeared in: SJH Nursing Officer - 2019

Explanation

Glucose is a carbohydrate (a simple sugar) and is not a structural component of lecithin.
Lecithin is a phospholipid, which is composed of a glycerol backbone, two fatty acids, a phosphate group, and choline.
Lipids that contain sugar moieties are classified as glycolipids, not phospholipids like lecithin.

Option A: Glycerol is the three-carbon backbone of lecithin and is released upon hydrolysis.
Option B: Lecithin contains two fatty acid chains esterified to the glycerol backbone, which are released during hydrolysis.
Option C: Choline is the nitrogenous base attached to the phosphate group in lecithin (phosphatidylcholine) and is a key product of its hydrolysis.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Composition and hydrolysis of phospholipids as background academic context rather than a clinical decision trigger.
A specific type of lecithin, dipalmitoyl lecithin, is the main component of lung surfactant, which is essential for preventing alveolar collapse. Its deficiency in premature infants causes Respiratory Distress Syndrome (RDS).
The Lecithin/Sphingomyelin (L/S) ratio in amniotic fluid is a crucial diagnostic test to assess fetal lung maturity. A ratio greater than 2:1 generally indicates mature lungs.
What if the question was about a glycolipid? If the question asked about the hydrolysis of a cerebroside, then glucose (or galactose) would be a correct product, along with a fatty acid and sphingosine.

How to Approach the Question

First, identify the core subject of the question, which is 'Lecithin' and the process 'hydrolysis'.
Recognize that 'except' makes this a negative question. You are looking for the option that is NOT a product.
Recall the chemical class of lecithin. Lecithin is a common name for phosphatidylcholine, a major type of phospholipid.
Mentally (or on paper) list the fundamental building blocks of a phospholipid: a glycerol backbone, two fatty acids, a phosphate group, and an attached alcohol (in this case, choline).
Compare this list of components with the given options: Glycerol, Fatty acid, and Choline are all on the list.
The remaining option, Glucose, is a sugar and not a standard component of a phospholipid. Therefore, it is the correct answer to the 'except' question.

Concept Tested & Keywords

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E6 textbook of Applied Biochemistry and Nutrition & DieteticsHarbans Lal (pp 26-464 of 479) p. 63-65

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 227-229

Practise the full SJH Nursing Officer - 2019

Attempt every question from this paper in a timed mock, then review the full solution for each one.