Chapter 16: Glycolysis Flashcards
Where does galactose enter the glycolytic pathway?
Galactose is converted in the liver to Glucose-6-phosphate
Fructose metabolism
Fructose is converted to fructose‑6‑phosphate in most tissues
Is converted to fructose‑1‑phosphate in the liver by the enzyme fructokinase
Fructose‑1‑phosphate is then cleaved by fructose‑1‑phoshate aldolase into DHAP and G3P
Glycolysis
Energy investment phase intermediates
Intermediates
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- Glucose
- Glucose 6-phosphate
- Fructose 6-phosphate
- Fructose 1,6-bisphosphate
- Glyceraldehyde 3-phosphate (G3P)
- Dihydroxyacetone phosphate (DHAP)
- DHAP converts to second molecule of G3P
Glycolysis
Energy investment phase enzymes
Enzymes
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- Hexokinase
- Phosphoglucoisomerase
- Phosphofructokinase
- Aldolase
- Triose phosphate isomerase
- Converts DHAP to G3P
Glycolysis
Energy payoff phase intermediates
Intermediates
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- 1,3-Bisphosphoglycerate (BPG)
- 3-Phosphoglycerate (PG)
- 2-Phosphoglycerate (PG)
- Phosphoenolpyruvate (PEP)
- Pyruvate
Glycolysis
Energy payoff phase enzymes
Enzymes
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- Glyceraldehyde 3-phosphate dehydrogenase
- Phosphoglycerokinase
- Phosphoglyceromutase
- Enolase
- Pyruvate kinase
Glycolysis
All enzymes
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- Hexokinase
- Phosphoglucoisomerase
- Phosphofructokinase
- Aldolase
- Triose phosphate isomerase
- Glyceraldehyde 3-phosphate dehydrogenase
- Phosphoglycerokinase
- Phosphoglyceromutase
- Enolase
- Pyruvate kinase
Glycolysis
All intermediates
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- Glucose
- Glucose 6-phosphate
- Fructose 6-phosphate
- Fructose 1,6-bisphosphate
- Glyceraldehyde 3-phosphate (G3P)
- Dihydroxyacetone phosphate (DHAP)
- DHAP converts to second molecule of G3P
- 1,3-Bisphosphoglycerate (BPG)
- 3-Phosphoglycerate (PG)
- 2-Phosphoglycerate (PG)
- Phosphoenolpyruvate (PEP)
- Pyruvate
Step 1 of glycolysis
Hexokinases transfers a phosphoryl group to carbon-6 utilizing one ATP
Traps glucose WITHIN the cell
IRREVERSIBLE
Step 2 of glycolysis
Phosphoglucose isomerase isomerizes glucose 6-phosphate to fructose 6-phosphate
Converts an aldose to a ketose
Step 3 of glycolysis
Phosphofructokinase transfers a phosphoryl group to carbon-1 utilizing one ATP
IRREVERSIBLE
Step 4 of glycolysis
Aldolase performs a reverse aldol reaction that cleaves fructose-6-phosphate into DHAP and G3P
Generates an aldehyde and ketone
Step 5 of glycolysis
Triose phosphate isomerase isomerizes DHAP to a second molecule of G3P
Step 6 of glycolysis
Glyceraldehyde 3-phosphate dehydrogenase oxidizes G3P via the addition of a phosphate group to carbon-1 forming 1,3-BPG
NAD+ gets reduced which produces one molecule of NADH
Step 7 of glycolysis
Phosphoglycerate kinase transfers the phosphoryl group on carbon-1 to ADP
Forms one molecule of ATP from each 1,3-BPG; total two ATP per each glucose molecule
Step 8 of glycolysis
Phosphoglycerate mutase moves the phosphoryl group from carbon-3 of 3-PG to carbon-2 forming 2-PG
Step 9 of glycolysis
Enolase performs a dehydration elimination reaction
Generates a resonance stabilized phosphoenolpyruvate molecule
Step 10 of glycolysis
Pyruvate kinase transfers phosphoryl group to ADP
Forms one molecule of ATP from each phosphoenopyruvate; total two ATP per each glucose molecule
IRREVERSIBLE
Phosphofructokinase regulation
Inhibited by an over-accumulation of ATP
Stimulated by high ratio of AMP:ATP
Most important control mechanism of glycolytic pathway
Hexokinase regulation
Inhibited by an over-accumulation of glucose-6-phosphate
Pyruvate kinase regulation
Inhibited by an over-accumulation of ATP
Stimulated by fructose 1,6-bisphosphate in a feed-forward mechanism
Glucose transporters in the liver and pancreatic β cells
GLUT2
Highest Km of all glucose transportes at 15−20mM to remove excess glucose from the blood
Glucose transporters in muscle and fat cells
GLUT4
Relatively low Km of 5mM to ensure adequate uptake of glucose
Warburg effect
Rapidly growing tumors obtain ATP by metabolizing glucose to lactate even in the presence of oxygen, a process termed aerobic glycolysis
Gluconeogenesis
Reverse process to glycolysis
Bypasses irreversible steps Gly-1, Gly-3, & Gly-10
Gly-10
- Pyruvate carboxylase (PC)
- Phosphoenolpyruvate carboxykinase (PEPCK)
Gly-3
- Fructose 1,6-bisphosphatase (FBPase)
Gly-1
- Glucose 6-phosphatase (G6Pase)
Step 1 of gluconeogenesis
Pyruvate carboxylase (PC) uses ATP to make oxaloacetate from pyruvate
Occurs in the mitochondiral matrix; oxaloacetate is subsequentally transported out of the mitochondria to the cytoplasm
Step 2 of gluconeogeneisis
Phosphoenolpyruvate carboxykinase (PEPCK) transfers a phosphate to oxaloacetate to form phosphoenolpyruvate
Step 9 of gluconeogenesis
Fructose-1,6-phosphatase (FBPase) removes a phosphate from fructose-1,6-bisphosphate to form fructose-6-phospate
Stimulate by glucagon and an increase in ATP
Inhibited by insulin and an increase in AMP
Step 11 of gluconeogenesis
Glucose 6-phosphate is transported into the lumen of the endoplasmic reticulum
Glucose-6-phosphatase dephosphorylates glucose-6-phosphate to glucose
G6Pase is an integral membrane protein on the inner surface of the endoplasmic reticulum
Hypoglycemic response
Glucagon stimulates PKA
FBPase is activated to stimulate gluconeogenesis
Glycolysis is inhibited
Hyperglycemic response
Insulin stimulates phosphoprotein phosphatase
Phosphofructokinase is activated which stimulates glycolysis
Gluconeogenesis is inhibited
Process to catabolize lactic acid
Cori cycle- when muscles are under anaerobic conditions and produce lactate, it can be transported to the liver and used in gluconeogenesis
