Chapter 34 HEIN

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Transcript Chapter 34 HEIN

Carbohydrate
Metabolism
Chapter 34
Hein * Best * Pattison * Arena
Version 1.0
Colleen Kelley
Chemistry Department
1 College
Pima Community
© John Wiley and Sons, Inc.
Chapter Outline
34.1 Metabolic Pathways
34.2 Exercise and Energy
Metabolism
34.3 The Bloodstream: A
Metabolic Connection
34. 4 Anaerobic Sequence
34.5 Citric Acid Cycle
(Aerobic Sequence)
34.6 Gluconeogenesis
34.7 Overview of Complex
Metabolic Pathways
34.8 Hormones
34.9 Blood Glucose and
Hormones
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Metabolic Pathways
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A metabolic pathway is a
series of biochemical
reactions that serve a
specific purpose.
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Exercise and
Energy Metabolism
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•
•
•
Everything we do requires metabolic
energy.
Metabolism is a complex interplay:
chemical reactions within cells lead
to chemical transport between cells.
Carbohydrate catabolism is designed
to release energy relatively quickly,
so this form of catabolism is
activated during strenuous muscular
exercise.
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Muscle Contraction
• When a muscle contracts, energy is
consumed.
• Muscle contraction uses ATP; ATP is in
short supply.
• Muscle tissue can contract for no more
than several seconds before the supply of
high-energy phosphate bonds is depleted.
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Muscle Contraction
• After the initial contraction, the muscle cells
look for other energy sources.
• Muscle glycogen is the next available source.
• This polymer breaks down to glucose, which is
oxidized to replenish the ATP supply.
• Because glucose oxidation is a complex process,
muscle contraction must proceed at a slower rate.
• This energy supply is only useful for about 2
minutes of work; muscles rapidly deplete their
glycogen stores and build up lactic acid.
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The Bloodstream: A
Metabolic Connection
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• The bloodstream transports
chemicals from one cell to another.
• Nutrients (e.g. glucose, amino
acids, and fatty acids) and oxygen
are delivered; metabolic products
(e.g. lactate) and carbon dioxide
are removed.
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Figure 34.1 Overview of carbohydrate metabolism
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• When blood glucose is in excess, it is
converted to glycogen in the liver and in
muscle tissue.
• Glycogen is a storage polysaccharide; it
quickly hydrolyzes to replace depleted
glucose supplies in the blood.
• The synthesis of glycogen from glucose is
called glycogenesis.
• The hydrolysis, or breakdown, of glycogen
to glucose is known as glycogenolysis.
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Anaerobic Sequence
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• In the absence of oxygen, glucose in
living cells is converted to a variety of
end products, including lactic acid (in
muscle) and alcohol (in yeast).
• At least a dozen reactions, many
different enzymes, ATP, and inorganic
phosphate (Pi) are required.
• Such a sequence of reactions from a
particular reactant to end product is
called a metabolic pathway.
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Embden-Myerhof pathway
• The anaerobic conversion of glucose to
pyruvate is known as the EmbdenMyerhof pathway.
• The sequence is a catabolic one in which
glucose is oxidatively degraded.
– D-glucose
Embden-Meyerhof pathway

2 pyruvate
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Glycolysis
• When lactate is the final product of
anaerobic glucose catabolism, the pathway
is termed glycolysis.
• What glycolysis does for the cell can be
summarized with the following net
chemical equation:
C6H12O6 + 2 ADP + 2 Pi 
2CH3CH(OH)COO- + 2 ATP + 150 kJ
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Citric Acid Cycle
(Aerobic Sequence)
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•
Since only a small fraction of the energy
that is potentially available from glucose
is liberated during anaerobic conversion
to lactate (glycolysis), lactate remains
valuable to the cells.
•
The lactate formed may be:
1) Circulated back to the liver and converted to
glycogen at the expense of some ATP
2) Converted back to pyruvate in order to enter
the citric acid cycle.
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Figure 34.3
The citric acid
cycle (Krebs
cycle). During
one cycle, (1)
the carbons
marked in
blue enter the
cycle, and (2)
the carbons
marked in red
are lost as
CO2.
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Energy Summation
glucose
glycolysis
2 ATP
2 lactate
citric acid cycle,
e- transport,
oxidative phosphorylation
+ 30 ATP
6 CO2
32 ATP
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Gluconeogenesis
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Gluconeogenesis
•
•
The formation of glucose from
noncarbohydrate sources is called
gluconeogenesis.
Most of the glucose formed during
gluconeogenesis comes from
lactate, certain amino acids, and the
glycerol of fats.
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Figure 34.4 An overview of gluconeogenesis.
All transformations except lactate to pyruvate
require a series of reactions.
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Overview of Complex
Metabolic Pathways
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Figure 34.5 A single-step oxidation process compared with a
multiple process: In the pathway, A, B, and C represent 26
hypothetical pathway intermediates.
Hormones
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Hormones
• Hormones are chemical substances that act
as control agents in the body, often
regulating metabolic pathways.
• Hormones help to adjust physiological
processes such as:
–
–
–
–
digestion
metabolism
growth
reproduction
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Hormones
• Hormones are often called the chemical
messengers of the body.
• They do not fit into any single structural
classification:
• Polypeptides or proteins
• Steroids
• Phenol or amino acid derivatives
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Blood Glucose and
Hormones
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• An adequate blood-glucose level must be
maintained to ensure good health.
• To achieve this goal, hormones regulate
and coordinate metabolism in specific
organs.
• The hormones control selected enzymes,
which, in turn, regulates the rates of
reaction in the appropriate metabolic
pathways.
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Figure 34.7
Conditions
related to the
concentration of
glucose in the
blood.
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Figure 34.8 Typical responses to a glucose-tolerance test.
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