30-07-2012, 04:00 PM
Gluconeogenesis; Regulation of Glycolysis AND Gluconeogenesis
10-gluconeo.ppt (Size: 580.5 KB / Downloads: 180)
Bypass of Pyruvate Kinase:
Pyruvate Kinase (last step of Glycolysis) catalyzes:
phosphoenolpyruvate + ADP pyruvate + ATP
For bypass of the Pyruvate Kinase reaction, cleavage of 2 ~P bonds is required.
DG for cleavage of one ~P bond of ATP is insufficient to drive synthesis of phosphoenolpyruvate (PEP).
PEP has a higher negative DG of phosphate hydrolysis than ATP.
Avidin, a protein in egg whites with a b barrel structure, tightly binds biotin.
Excess consumption of raw eggs can cause nutritional deficiency of biotin.
The strong avidin-to-biotin affinity is used by biochemists as a specific "glue."
If it is desired to bind 2 proteins together for an experiment, biotin may be covalently linked to one protein and avidin to the other.
Explore with Chime the biotinyl domain of a carboxylase and the avidin-biotin complex.
The source of pyruvate and oxaloacetate for gluconeogenesis during fasting or carbohydrate starvation is mainly amino acid catabolism.
Some amino acids are catabolized to pyruvate, oxaloacetate, or precursors of these.
Muscle proteins may break down to supply amino acids. These are transported to liver where they are deaminated and converted to gluconeogenesis inputs.
Glycerol, derived from hydrolysis of triacylglycerols in fat cells, is also a significant input to gluconeogenesis.
Energy dissipation by the Cori Cycle, which expends 6 ~P in liver for every 2 ~P produced via Glycolysis for utilization within the tumor, is thought to contribute to the weight loss that typically occurs in late-stage cancer even when food intake remains normal.