Practice question

SGLT1, SLC5A1, is apical sodium-glucose cotransporter highly expressed in brush border of small intestinal enterocytes and S3 segment of kidney proximal tubule. It operates as secondary active transporter, not primary ATPase nor simple facilitator. Stoichiometry of two Na+ to one glucose allows accumulation of glucose against its concentration gradient using electrochemical sodium gradient established by basolateral Na+/K+ ATPase that maintains low intracellular Na+. Transport follows alternating access mechanism: outward-open binds Na+ increasing glucose affinity, sugar binding triggers outward-to-inward switch releasing Na+ and glucose inside. Imported glucose exits basolaterally via facilitative GLUT2. This coupling explains oral rehydration therapy where sodium and glucose coadministration drives water absorption. Inhibitors include phlorizin natural glucoside and selective SGLT2 inhibitors gliflozins used for diabetes. Genetic defects cause glucose-galactose malabsorption with severe diarrhea, highlighting nutritional importance of sodium-coupled concentrative uptake mechanism. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.