Download 2.-lactic-acid-metabolism

(8) Energy systems in muscle cells
Energy
systems in
muscle cells
(A)
Creatine
Phosphate
(B) Lactic Acid
Metabolism
(C)
Types of skeletal
muscle fibres
(b) Energy systems in muscle
cells
• State the alternative route of pyruvate
and when this occurs
• Explain how muscle fatigue develops
• Explain what is meant by the term
‘oxygen debt’ and how it can be ‘repaid’
What can you remember about
these words?
• Lactic acid
•Muscle fatigue
•Oxygen debt
LACTIC ACID METABOLISM
(occurs in the absence of oxygen)
 In the absence of oxygen, neither the citric acid cycle nor the electron
transport chain can occur!
 Therefore a cells only source of ATP is through glycolysis.
 When glucose is broken down into pyruvate, 2 ATP and 2NADH are made.
 This is followed by the conversion of pyruvate into lactic acid AND THE
TRANSFER OF HYDROGEN from NADH.
 Since the hydrogen has been removed, therefore regenerating NAD. (NAD
must be present for glycolysis to continue).
 But as more and more lactic acid builds up, muscle fatigue is caused and an
oxygen debt is created.
NAD
Glucose
2 ADP+Pi
NADH
Pyruvate
2 ATP
Oxygen debt
builds up
Oxygen debt
repaid
(through aerobic
respiration)
Lactic Acid
1
• During vigorous exercise,
the muscle cells do not
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get sufficient oxygen
to support the electron
2
3 chain.
transport
• Under these conditions, pyruvate is converted to
lactic4 acid. This conversion involves the transfer of
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hydrogen
from the NADH produced during
glycolysis to pyruvic acid to produce lactic acid.
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This regenerates
the NAD needed to maintain ATP
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production through glycolysis.
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• Lactic acid accumulates in muscle causing fatigue.
• The oxygen debt is repaid when exercise is
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complete, as this allows respiration
to provide the
10 acid
energy to convert lactic acid back to pyruvic
and glucose in the liver.
(b) Energy systems in muscle
cells
• State the alternative route of
pyruvate and when this occurs
• Explain how muscle fatigue develops
• Explain what is meant by the term
‘oxygen debt’ and how it can be
‘repaid’