Sources that provide ATP in working muscle •
Figure 6.7
From
blood
Muscle glycogen
Glucose
[
1
1
-----1
Glycolysis
i-----1
(net gain)
2 Pyruvic acid
2 Lactic acid
Into blood
a.
Creatine-phosphate transfers phosphate from
ADP to make ATP. This process gets
exhausted within 15 seconds, so it is good for
quick bursts of muscle activity. Once at rest,
the muscle makes ATP and regenerates
creatine phosphate.
b. Anaerobic respiration (glycolysis) breaks
glucose from glycogen into pyruvic acid
through a series of steps. The ATP is used in
muscle contraction and the pyruvic acid gets
converted to lactic acid. Lactic acid is what
makes muscles sore. Glycolysis provides ATP
for a further 30-60 seconds.
Fatty acids liberated
Pyruvic acid
from adipose cells
from glycolysis
Amino acids from
protein breakdown
Oxygen from
hemoglobin in blood
or from myoglobin
in muscle fibers
c.
Aerobic respiration requires oxygen from the blood or a muscle
protein called myoglobin. Pyruvic acid gets broken down into
carbon dioxide and water. The energy released gets captured to
make ATP and some gets lost as heat. Aerobic respiration can
also use amino acids and fatty acids to make ATP. This process
provides more ATP than the others and can last a long time
(e.g., minutes to hours of muscle activity).
1~P+ hours
162 CHAPTER 6
The Muscular System
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