Entrance Exams
Govt. Exams
Simple carbohydrates include monosaccharides (glucose, fructose, galactose) and oligosaccharides (2-10 units like sucrose, maltose, lactose). Complex carbohydrates are polysaccharides with >10 units (starch, glycogen, cellulose).
In the Warburg effect, PFK-2 and PKM2 are upregulated. PFK-2 produces fructose-2,6-bisphosphate (a potent PFK-1 activator), while PKM2 (pyruvate kinase isoform) is upregulated in cancer cells. PKM2 also has non-glycolytic functions in cancer metabolism.
The PFK reaction is highly exergonic (ΔG°' = -14.2 kJ/mol) and is essentially irreversible. During gluconeogenesis, fructose-1,6-bisphosphatase catalyzes the reverse reaction. This is a major control point in carbohydrate metabolism.
PFK is inhibited by high ATP, citrate (signal of sufficient acetyl-CoA), and low pH. In aerobic conditions, efficient oxidative phosphorylation produces sufficient ATP, reducing need for glycolysis (Pasteur effect). Citrate is an allosteric inhibitor of PFK.
Classic galactosemia results from deficiency of galactose-1-phosphate uridyltransferase (GALT), preventing conversion of galactose-1-phosphate to UDP-galactose. Leads to accumulation of galactose-1-phosphate and galactitol (in polyol pathway), causing cataracts, intellectual disability, and liver damage.
The oxidative phase of PPP generates 2 NADPH per glucose-6-phosphate, essential for fatty acid synthesis, cholesterol synthesis, and antioxidant defense (glutathione reduction). This is particularly important in adipose tissue, liver, and RBCs.
Cellulose contains β(1→4) glycosidic bonds linking glucose units, making it indigestible to humans (no cellulase enzyme). Starch contains α(1→4) bonds, which are digestible.
HbA1c is formed through non-enzymatic glycation of hemoglobin by glucose, reflecting average blood glucose over 2-3 months (RBC lifespan). Normal HbA1c <5.7%, diagnostic for diabetes ≥6.5%.
The anomeric carbon (C1 in glucose) is the carbon that becomes chiral when the open-chain form cyclizes to form the hemiacetal. This is the site of α/β isomerism.
Pyruvate carboxylase catalyzes the first committed step of gluconeogenesis, converting pyruvate to oxaloacetate. Lactate is converted to pyruvate by LDH, then to glucose via gluconeogenesis.