Glucose Metabolism

Glyconeogenesis

glucose → glycogen

glycogenolysis

glycogen → glucose

gluconeogenesis

lactate → glucose

glycolysis

glucose → pyruvate

acetyl coA

product of most major energy-generating pathways of cells

pentose phosphate pathway

glucose → ribose 5-phosphate

prep phase (2 ATP invested, 5 steps), payoff phase (4 ATP made, 5 steps)

2 phases of glycolysis

hexokinase, phosphofructokinase 1 (PFK1), both use ATP

enzymes that add phosphate group to prevent molecule from “escaping” in glycolysis

add a phosphate, make it a pentose ring, add another phosphate, split in half

basic steps of the prep phase of glycolysis

glyceraldehyde 3-phosphate, dihydroxyacetone phosphate

end products of the prep phase of glycolysis

phosphoglycerate kinase (produces the first ATP), pyruvate kinase (produces the second ATP)

enzymes that catalyze two substrate-level phosphorylations that occur in the payoff phase of glycolysis

hydrogen removed (added to NADH), inorganic phosphate added then removed to produce ATP, terminal phosphate moved to center of molecule and extra OH removed to make a higher energy state, last phosphate removed to create ATP and pyruvate

basic steps of the payoff phase of glycolysis

2 pyruvate, 2 NADH, 2 ATP

end products of glycolysis of one molecule of glucose

oxidation of glyceraldehyde 3-phosphate using glyceraldehyde 3-phosphate dehydrogenase to produce 1, 3-bisphosphoglycerate

first reaction of payoff phase of glycolysis that produces NADH and creates a high-energy phosphate compound that will lead to ATP production

substrate-level phosphorylation

enzyme-catalyzed reaction that produces ATP or GTP

oxidative phosphorylation

electron transport by ETC is used to provide energy for ATP synthesis

phosphoglycerate kinase turning 1,3-bisphosphoglycerate to 3-phosphoglycerate and pyruvate kinase turning phosphoenolpyruvate to pyruvate

two substrate-level phosphorylation steps (ADP-ATP), irreversible

oxidoreduction reaction catalyzed by lactate dehydrogenase

NAD+ regeneration step

hexokinase, 6-phosphofructo-1-kinase (major), pyruvate kinase

regulatory/irreversible reactions in glycolysis

ATP (don’t need more), citrate (signal that fatty acids are being used and glucose can be saved), pH (pyruvate=acid, too much leads to protein damage)

inhibitors of 6-phosphofructo-1-kinase

cytosol

where does glycolysis occur

mitochondria

where does the citric acid/Krebs cycle occur

pyruvate oxidatively decarboxylated to acetate, which is degraded to CO2, producing some ATP and more NADH

overview of the Krebs/TCA/citric acid cycle

oxidation of alpha ketoglutarate to succinyl-CoA and CO2

irreversible reactions of krebs/CA cycle

oxidative decarboxylation

removing a carboxyl group to form NADH

4 CO2, 6 NADH, 2 FADH2, 2 GTP

products of one turn of the citric acid cycle (2 acetyl coA from glycolysis)

citrate synthase (ATP, NADH, and succinyl-coA inhibit), isocitrate dehydrogenase (ATP inhibits, ADP and NAD+ activate), and alpha ketoglutarate dehydrogenase (NADH and succinyl-CoA inhibit, AMP activates)

sites of regulation for CAC/Krebs cycle

pyruvate is converted to acetyl-CoA by pyruvate dehydrogenase (regulated, controls rate of aerobic oxidation of glucose)

pre-citric acid cycle step

electron transport

electrons carried by reduced coenzymes NADH and FADH2 are passed through a chain of proteins and coenzymes to drive the generation of a proton gradient across the inner mitochondrial membrane

oxidative phosphorylation

proton gradient runs downhill to drive ATP synthesis at the inner mitochondrial membrane