Carbohydrates 2 Flashcards
Glycolysis Stage 1
Phosphorylation of glucose to trap it in cell; uses energy to destabilize molecule to make break down easier in stage 2 (2 ATPs used)
Glycolysis Stage 2
6C F-1,6-BisP spilts into 2 3C molecules (DHAP and GAP; DHAP CANNOT proceed on in glycolysis pathway, must be converted to GAP or to glycercol for synthesis of storage fat)
Glycolysis Stage 3
3C GAP molecule is oxidized in 5 steps to generate pyruvate; energy-yielding phase; 2 molecules of ATP are synthesized by substrate level phosphorylation; 2 ATP’s per 1 GAP so 4 ATP’s per 1 glucose molecule
Degradation of Fructose: Liver and Muscle
Liver—Fructose metabolized in liver; converted to F-1-P by fructokinase and then further cleaved into DHAP enters at Stage 2 glycolysis; remember fructose doesn’t trigger insulin release
Muscle—fructose is -P’d by hexokinase, then enters glycolysis
Degradation of Galactose
must be converted to glucose; is first -P’d then linked to UDP, UDP-galactose is then transformed into UDP-glucose; in pathway once Galac-1-P is formed it must be degraded–but if accumulated; also the UDP is recycled back in reaction
Essential Fructosuria
Deficiency of liver fructokinase, fructose is NOT utilized and excreted in urine; no harmful effects
Hereditary Fructose Intolerance
Deficiency in Aldolase B enzyme; fructose-1-P CANNOT be converted to DHAP and then is accumulated in the liver; liver phosphate pools are depleted and then it cannot break down glycogen; enlarged liver, coma, hypoglycemia, jaundice, decrease liver function
Galactosemia
failure to utilize galactose in glycolysis; 3 types based on enzyme effected— galactokinase, galactose-1-phosphate uridyltransferase, UDP-galactose epimerase; intellectual disability, vision loss, liver damage, jaundice
Regulatory Signals of Glycolysis
Intermediates of energy metabolism (ATP, citrate); Hormones (insulin, glucagon, epinephrine); Fructose-2,6-BisP
3 Regulated Steps of Glycolysis
Phosphofructokinase, Hexokinase, pyruvate kinase
Regulation of Phosphofructokinase
most important regulated step/rate controlling step; F-6-P –> F-1,6-P
inhibited by ATP, citrate
stimulated by hormones (via F-2,6-BisP), ADP and AMP
Regulation of Hexokinase
Glucose –> G-6-P; Stimulated by insulin
Inhibited by end product (G-6-P), acetyl-CoA
Regulation of Pyruvate Kinase
PEP –> Pyruvate; stimulated by F-2,6-BisP, insulin
inhibited by ATP
Fructose-2,6-Bisphosphate
synthesized from F-6-P; accelerator of glycolysis; regulates PFK1/Fructose bisphosphatase
Common Misconception about Glycolysis
glycolysis is NOT performed solely for energy generation; it is also for removal of glucose from circulation and building up long term stores of energy–if glucose is available, glycolysis is very active regardless of cellular energy demands
Regulation of Glycolysis in Starvation State
Glucagon activates PKA via cAMP cascade; PKA inhibits PFKII so F-2,6-BisP is no longer made from F-6-P; w/o F-2,6-BisP then gluconeogenesis can proceed uninhibited
Regulation of Glycolysis in Well Fed State
Insulin inhibits PKA (cAMP cascade not started); inhibition of PKA leads to active PFKII which produces F-2,6,-BisP; F-2,6-BisP upregulates PFKI and glycolysis proceeds while GNG is shutdown
PFKII
F-6-P –> F-2,6-BisP; upregulated by AMP, F-6-P and downregulated by PKA
Glycerol Phosphate Shuttle
muscle and brain; gets electrons from NADH in cytosol and puts them on FADH in mito matrix; less efficient than other shuttle; for tissues that utilize a lot of glucose; loss of 1 ATP formation by going from NADH to FADH; glycercol-3-phosphate dehydrogenase
Malate-Aspartate Shuttle
Liver/heart tissue; NADH reduces OAA to malate, malate transported across inner mito membrane, inside it is converted back to OAA and NADH is produced; more efficient than other shuttle
If O2 is not available–Fermentation
pyruvate must accept electrons from NADH to regenerate NAD+ for glycolysis; pyruvate–> lactate; occurs in RBC’s since they have no mito; lactate taken up by liver; accumulation = lactic acidosis
Pyruvate Kinase Deficiency
deprives RBC’s of ATP; leads to lysis of RBC’s b/c membrane potential cannot be maintained; hemolytic anemia;
Arsenate Poisoning
Aresnate can micmic phosphate; causes glycolysis to not be able to produce ATP (via substrate level -P); BAD for RBC’s = hemolytic anemia
Cori Cycle
RBC’s/muscles convert pyruvate to lactate; lactate enters circulation and is picked up by liver; liver uses GNG to convert lactate–> pyruvate–> glucose; glucose sent back into circulation for RBS’s to utiltize to create ATP
