Govt. Exams
Entrance Exams
The Cori cycle involves lactate produced in muscles being transported to the liver where it undergoes gluconeogenesis to form glucose, which is sent back to muscles. This is crucial during anaerobic exercise.
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.
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.
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).
Essential fructosuria results from fructokinase deficiency. It is benign because fructose is simply excreted in urine without accumulating in tissues or causing metabolic harm.
Through the non-oxidative phase of the pentose phosphate pathway, sugars are rearranged to produce fructose-6-phosphate and glyceraldehyde-3-phosphate, which directly enter glycolysis.
Glucuronic acid, derived from glucose, is a key component of glycosaminoglycans like heparin, hyaluronic acid, and chondroitin sulfate, providing their acidic properties.
Ethanol metabolism consumes NAD+, reducing the NAD+/NADH ratio. This inhibits NAD+-dependent dehydrogenases including those in gluconeogenesis and lactate oxidation, leading to lactate accumulation.
