Which of the following transports glucose and galactose?

DSSSB 12 August 2024

Biochemistry & Nutrition

Easy

Appeared in: DSSSB 12 August 2024

Explanation

SGLT-1, which stands for Sodium-Glucose Linked Transporter 1, is a co-transporter that moves both glucose and galactose from the intestinal lumen into the enterocytes.
This process is a form of secondary active transport, meaning it uses the energy stored in the sodium ion (Na+) gradient to move the sugars against their concentration gradient.
This transporter is located on the apical membrane of epithelial cells in the small intestine and is crucial for absorbing these two key monosaccharides from the diet.

Option A: GLUT-5 is the primary transporter for fructose. It operates via facilitated diffusion and does not transport glucose or galactose.
Option C: VLDL (Very Low-Density Lipoprotein) is a particle that transports endogenous lipids, primarily triglycerides, from the liver to other tissues. It is not involved in carbohydrate transport. The '-4' suffix is not standard nomenclature.
Option D: HDL (High-Density Lipoprotein) is involved in reverse cholesterol transport, carrying cholesterol from peripheral tissues back to the liver for excretion or recycling. It does not transport sugars. The '-4' suffix is not standard nomenclature.

Clinical Relevance

Nursing practice connection: Knowing Mechanism of monosaccharide transport in the small intestine helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
The co-transport of sodium and glucose by SGLT-1 is the physiological principle behind Oral Rehydration Therapy (ORT). The glucose in ORS solutions enhances the absorption of sodium and, consequently, water, which is vital for treating dehydration from conditions like cholera and diarrhea.
A rare genetic disorder, glucose-galactose malabsorption, is caused by a defect in the SGLT-1 transporter. Infants with this condition suffer from severe, life-threatening diarrhea from birth when fed milk (which contains lactose, broken down into glucose and galactose).
What if? If a patient is taking an SGLT-2 inhibitor for type 2 diabetes, it will block glucose reabsorption in the kidneys, leading to glucose excretion in the urine. This mechanism is specific to the kidneys and does not affect the SGLT-1 transporter in the intestine, so dietary glucose absorption remains unchanged.

How to Approach the Question

First, identify the key molecules in the question: glucose and galactose. Recognize that these are both monosaccharides (simple sugars).
Next, recall the different mechanisms for nutrient absorption in the small intestine, specifically for carbohydrates.
Analyze the options provided. VLDL and HDL are lipoproteins involved in fat metabolism, so they can be immediately eliminated as incorrect.
This leaves two carbohydrate transporters: GLUT-5 and SGLT-1.
Differentiate between their functions: recall that GLUT-5 is the specific transporter for fructose.
Therefore, SGLT-1 must be the transporter for glucose and galactose. Its full name, Sodium-Glucose Linked Transporter, serves as a strong clue.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 2A p. 194-196

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 465-467