Govt. Exams
Entrance Exams
NADPH from the pentose phosphate pathway serves as the primary reducing agent for biosynthetic reactions, especially fatty acid and cholesterol synthesis. It is also crucial for antioxidant defense (glutathione reduction) and biosynthesis of nucleotides.
McArdle disease involves glycogen phosphorylase deficiency in muscle, preventing glycogen breakdown during exercise. This causes exercise intolerance with muscle pain, cramps, fatigue, and myoglobinuria. The 'second wind' phenomenon (improved symptoms after 10 minutes as blood glucose increases) is characteristic.
Hexokinase is inhibited by its product glucose-6-phosphate, making it rate-limiting. Glucokinase, found in liver, is NOT inhibited by G6P, allowing continuous glucose phosphorylation in fed state. This differential regulation is crucial for glucose sensing.
During prolonged fasting, ketone bodies produced from hepatic fatty acid oxidation become the preferred fuel for the brain (up to 60% of energy needs), reducing the requirement for gluconeogenesis and preserving muscle protein.
2,3-BPG is synthesized from 1,3-bisphosphoglycerate by bisphosphoglycerate mutase. 2,3-BPG binds to hemoglobin, decreasing its oxygen affinity, facilitating oxygen release to tissues. This shunt allows RBCs to regulate oxygen delivery without producing ATP.
The branching enzyme (amylo-1,6-transglucosidase) transfers segments of α-1,4-linked glucose to create α-1,6-branch points, making glycogen more soluble and accessible. Its deficiency causes Andersen disease with abnormal glycogen accumulation.
GLUT4 is the insulin-dependent glucose transporter found primarily in skeletal muscle and adipose tissue. Impaired GLUT4 translocation or function is a hallmark of type 2 diabetes, leading to reduced muscle glucose uptake.
Both phosphoglycerate kinase (1,3-bisphosphoglycerate → 3-phosphoglycerate) and pyruvate kinase (phosphoenolpyruvate → pyruvate) catalyze substrate-level phosphorylation in glycolysis, directly generating ATP.
During the fight-or-flight response, epinephrine activates adenylyl cyclase leading to increased cAMP and PKA activation. PKA phosphorylates and activates glycogen phosphorylase, promoting glycogen breakdown for rapid glucose availability.
The oxidative phase of the pentose phosphate pathway requires NADP⁺, which is derived from Vitamin B3, but Riboflavin (B2) is needed for flavin-dependent enzymes. Actually, the answer should be B3/Niacin for NADP⁺. This requires Niacin. Correcting: Riboflavin is required as FAD in various pathways. NADP⁺ comes from Niacin.
