Regulated glycolytic reactions are

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Regulated glycolytic reactions are not at
equilibrium in the cell
Regulation points
Regulation points
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Rate-limiting steps are regulated reactions in
the pathway that operate away from equilibrium
are regulated. At these reaction steps there is a
build-up of substrates because the substrates are
not converted to products fast enough. Typically
these reactions are regulated.
DG lt 0
B C
DG 0
C D
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Regulation of Glycolysis
Inhibitors
Activators
Hexokinase
Glucose 6-phosphate
ADP, AMP, Fructose 2,6P
ATP, citrate, PEP
Phosphofructokinase
ATP
Pyruvate kinase
CITRIC ACID CYCLE (ATP, citrate)
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Regulatory Enzymes exhibit decreased or
increased activity in response to certain signals.
Allosteric regulation the enzymes activity is
regulated through reversible, noncovalent binding
of a small molecule regulator (an allosteric
modulator).
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The Fates of Glucose
Glycogen
Pentose Phosphate Pathway
Gluconeogenesis
Glycolysis
Lactate (anaerobic)
Citric acid cycle (aerobic)
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Gluconeogenesis Synthesis of glucose from
non-hexose precursors (lactate, fatty acids and
amino acids)
lactate
Chapter 20. Figure 20-2
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Pentose Phosphate Pathway
Glycolysis
Pentose Phosphate Pathway (a) Produces NADPH, a
reducing agent needed for anabolic
reactions. (b) Pentose type
sugars. Required for the production nucleic
acids
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Glycogen Breakdown
Glycogen Synthesis
Glucose
Glycogen
Glucose
Glycogen Breakdown
R
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Glycogen Breakdown
Glycogen Synthesis
Glucose
Glycogen
Glucose
Glycogen Synthesis
R
Chapter 20. Figure 20-12
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The liver is the central control point for
regulating blood glucose levels
Heavy activity in muscle consumes muscle glycogen
Muscle glycogen reserves are rebuilt during times
of less intense activity
Gluconeogenesis in liver converts lactate to
glucose
Suggested Reading Chapter 23 869-884
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The liver is the central control point for
regulating blood glucose levels
Brain
Liver
glycogen
Muscle tissue
glycogen
rest
Dietary and intrinsic carbohydrates, proteins,
and lipids
glucose
glucose
active
lactate
lactate
Its critical that blood glucose levels are
maintained within a defined concentration range.
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Low Blood Glucose (Hungry. Several hours after
eating)
Increase glycogen break down
Increased gluconeogenesis
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Low Blood Glucose (Panic reaction)
Epinephrine (aka Adrenaline) mediates the fight
or flight response
Effects similar to glucagon. It mobilizes glucose
from glycogen. In contrast, it also promotes
glucose catabolism in muscle tissue (for
production of ATP for activity).
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Glucagon/Epinephrine control of glycogen
synthesis/degradation
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Signal cascade initiated by epinephrine
Optional reading Page 449-454
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Signal cascade initiated by epinephrine
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Glucagon control of glycolysis/gluconeogenesis (th
e fructose 2,6-bisphosphatate connection)
Glucogon controls the production of fructose
2,6-bisphosphatate
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High Blood Glucose
Insulin lowers blood glucose levels