Govt Exams
PFK-1 catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate and is the rate-limiting enzyme of glycolysis. It is negatively regulated by ATP and citrate, making it a key control point.
In Pompe disease, acid α-glucosidase deficiency prevents lysosomal glycogen hydrolysis. Normally structured glycogen accumulates in lysosomes (unlike the abnormal structures seen in Type IV GSD), causing lysosomal dysfunction and cellular damage.
Transketolase requires thiamine pyrophosphate (TPP/vitamin B1) as a cofactor to transfer 2-carbon ketol groups between sugar phosphates in the non-oxidative phase of the pentose phosphate pathway.
Mannose differs from glucose only at the C2 position (the configuration of the -OH group and -H). Therefore, mannose is the C2 epimer of glucose.
While this is primarily a hemoglobin question, HbF (with γ-chains instead of β-chains) does not polymerize like HbS or aggregate like HbC, reducing hemolysis and RBC sickling/crystallization.
After liver glycogen is depleted (8-12 hours), gluconeogenesis becomes the primary source of glucose. The substrates are amino acids (from muscle proteolysis) and glycerol (from lipolysis).
GLUT4 is the insulin-responsive glucose transporter present in skeletal muscle and adipose tissue. Insulin signaling causes GLUT4 translocation to the cell membrane, increasing glucose uptake.
Phosphofructokinase-1 (PFK-1) is the rate-limiting enzyme of glycolysis. It is inhibited by ATP and citrate (signals of sufficient energy) and activated by AMP and ADP (signals of energy depletion).
Muscle phosphorylase deficiency prevents glycogen breakdown, depriving muscles of glucose-1-phosphate during exercise, causing severe energy crisis, fatigue, cramps, and myoglobinuria.
Glycogen synthase catalyzes the transfer of glucose from UDP-glucose to the C4-OH group of the terminal glucose in glycogen, forming α-1,4-glycosidic bonds.