The pentose phosphate pathway
- is an alternative pathway for the oxidation of glucose.
- produces the coenzyme NADPH and give-carbon pentoses.
NADPH, the reduced form of NADP+, is an important coenzyme required in the anabolic pathways,
including the biosynthesis of nucleic acids, cholesterol, and fatty acids in the liver and fat cells.
Hexose used to make energy
Pentose used to make DNA
Everything that comes off these structures it then makes an imprint to be used when making the DNA
The pentose phosphate pathway begins with glucose-6-phosphate from reaction 1 in glycolysis, which is
converted to ribulose-5-phosphate and requires two NADP+.
Ribulose-5-phosphate is isomerized by the catalyst phosphopentose isomerase to ribose-5-phosphate, an
important component of nucleotides such as ATP, GTP, UTP, NAD+, FAD and RNA.
- The pyruvate produced from glucose can now enter pathways that continue to extract energy.
- The available pathway depends on whether there is sufficient oxygen in the cell.
- Under aerobic conditions, oxygen is available to convert pyruvate to acetyl coenzyme A (acetyl
CoA) and CO2.
- When oxygen levels are low, pyruvate is reduced to lactate.
Under aerobic conditions (oxygen present), pyruvate moves from the cytosol into the mitochondria to be
oxidized further. It is also oxidized when a carbon atom is removed as CO2 as the coenzyme NAD+ is
reduced. The resulting two-carbon acetyl group is attached to CoA producing acetyl CoA, and important
intermediate in many metabolic pathways.
Lactate dehydrogenase → very important enzyme for us
Glycogen: Energy Storage
Excess glucose is used to replenish energy reserves by synthesizing glycogen, which is stored in your
muscles and liver.
Glycogen →
- Is a polymer of glucose with alpha (1 → 4)-glycosidic bonds and multiple branches attached by
alpha (1 → 6)-glycosidic bonds.
- Is formed when high levels of glucose-6-phosphate are formed in the first reaction of glycolysis.
- Is not formed when energy stored (glycogen) is full, which means that additional glucose is
converted to triacylglycerols and stored as body fat.
Glycogenesis →
- Is the metabolic process of converting glucose molecules into glycogen.
- Produced glucose-6-phosphate in reaction 1 of glycolysis.
, Glycogenesis: Reaction 1 →
Reaction 1, isomerization: Glycogen synthesis begins with
- The conversion of glucose-6-phosphate to the isomer glucose-1-phosphate
- The enzyme phosphoglucomutase catalyzes the shift of a phosphate group between carbon atoms.
Glycogenesis: Reaction 2 →
In reaction 2, activation,
- Glucose-1-phosphate is activated before addition to the glycogen chain
- Energy is released when pyrophosphorylase catalyzes the reaction
- The high-energy compound UTP transfers UMP to glucose-1-phosphate to give UDP-glucose and
pyrophosphate, PPi.
Glycogenesis: Reaction 3 →
In reaction 3, glycogen synthesis,
- Glycogen synthase catalyzes breaking of the phosphate bond to glucose in UDP-glucose
- Glucose is released, forming an alpha (1 → 4) glycosidic bond with the end of a glycogen chain.
Glycogenolysis: Reactions 1 and 2 →
In glycogenolysis, glycogen is broken down to glucose.
In reaction 1, phosphorolysis,
- Glucose molecules are removed from the glycogen chain
- Glucose molecules are phosphorylated by glycogen phosphorylase to yield glucose-1-phosphate.
In reaction 2, hydrolysis (alpha-1,6)
- Glycogen phosphorylase cleaves alpha(1 → 4) links until only one glucose remains bonded to the
main chain.
- A debranching enzyme breaks alpha (1 → 6) glycosidic bonds so branches of glucose molecules
can be hydrolyzed by reaction 1.
Regulation of Glycogen Metabolism
The brain, skeletal muscles, and red blood cells require large amounts of glucose to function properly.
To protect the brain, hormones with opposing actions control blood glucose levels such as
- Glucagon
- Insulin
- Epinephrine
Glycogenolysis → breaking down (catabolism)
Glycogenesis → making of the entity
Slide 48 on main left off
- is an alternative pathway for the oxidation of glucose.
- produces the coenzyme NADPH and give-carbon pentoses.
NADPH, the reduced form of NADP+, is an important coenzyme required in the anabolic pathways,
including the biosynthesis of nucleic acids, cholesterol, and fatty acids in the liver and fat cells.
Hexose used to make energy
Pentose used to make DNA
Everything that comes off these structures it then makes an imprint to be used when making the DNA
The pentose phosphate pathway begins with glucose-6-phosphate from reaction 1 in glycolysis, which is
converted to ribulose-5-phosphate and requires two NADP+.
Ribulose-5-phosphate is isomerized by the catalyst phosphopentose isomerase to ribose-5-phosphate, an
important component of nucleotides such as ATP, GTP, UTP, NAD+, FAD and RNA.
- The pyruvate produced from glucose can now enter pathways that continue to extract energy.
- The available pathway depends on whether there is sufficient oxygen in the cell.
- Under aerobic conditions, oxygen is available to convert pyruvate to acetyl coenzyme A (acetyl
CoA) and CO2.
- When oxygen levels are low, pyruvate is reduced to lactate.
Under aerobic conditions (oxygen present), pyruvate moves from the cytosol into the mitochondria to be
oxidized further. It is also oxidized when a carbon atom is removed as CO2 as the coenzyme NAD+ is
reduced. The resulting two-carbon acetyl group is attached to CoA producing acetyl CoA, and important
intermediate in many metabolic pathways.
Lactate dehydrogenase → very important enzyme for us
Glycogen: Energy Storage
Excess glucose is used to replenish energy reserves by synthesizing glycogen, which is stored in your
muscles and liver.
Glycogen →
- Is a polymer of glucose with alpha (1 → 4)-glycosidic bonds and multiple branches attached by
alpha (1 → 6)-glycosidic bonds.
- Is formed when high levels of glucose-6-phosphate are formed in the first reaction of glycolysis.
- Is not formed when energy stored (glycogen) is full, which means that additional glucose is
converted to triacylglycerols and stored as body fat.
Glycogenesis →
- Is the metabolic process of converting glucose molecules into glycogen.
- Produced glucose-6-phosphate in reaction 1 of glycolysis.
, Glycogenesis: Reaction 1 →
Reaction 1, isomerization: Glycogen synthesis begins with
- The conversion of glucose-6-phosphate to the isomer glucose-1-phosphate
- The enzyme phosphoglucomutase catalyzes the shift of a phosphate group between carbon atoms.
Glycogenesis: Reaction 2 →
In reaction 2, activation,
- Glucose-1-phosphate is activated before addition to the glycogen chain
- Energy is released when pyrophosphorylase catalyzes the reaction
- The high-energy compound UTP transfers UMP to glucose-1-phosphate to give UDP-glucose and
pyrophosphate, PPi.
Glycogenesis: Reaction 3 →
In reaction 3, glycogen synthesis,
- Glycogen synthase catalyzes breaking of the phosphate bond to glucose in UDP-glucose
- Glucose is released, forming an alpha (1 → 4) glycosidic bond with the end of a glycogen chain.
Glycogenolysis: Reactions 1 and 2 →
In glycogenolysis, glycogen is broken down to glucose.
In reaction 1, phosphorolysis,
- Glucose molecules are removed from the glycogen chain
- Glucose molecules are phosphorylated by glycogen phosphorylase to yield glucose-1-phosphate.
In reaction 2, hydrolysis (alpha-1,6)
- Glycogen phosphorylase cleaves alpha(1 → 4) links until only one glucose remains bonded to the
main chain.
- A debranching enzyme breaks alpha (1 → 6) glycosidic bonds so branches of glucose molecules
can be hydrolyzed by reaction 1.
Regulation of Glycogen Metabolism
The brain, skeletal muscles, and red blood cells require large amounts of glucose to function properly.
To protect the brain, hormones with opposing actions control blood glucose levels such as
- Glucagon
- Insulin
- Epinephrine
Glycogenolysis → breaking down (catabolism)
Glycogenesis → making of the entity
Slide 48 on main left off
