Transcript Limits of Human Performance

ATP homeostasis
Energy systems homeostasis
• ATP
– Common metabolic
intermediate
– Powers muscular
contraction
– Cell work
– Well-maintained over
wide variations in
energy turnover
Energy homeostasis
• 3 basic energetic systems
– Immediate (ATP-PCr)
– Non-oxidative: anaerobic glycolysis
– Oxidative: oxidative phosphorylation
Immediate energy systems
Ca2+
• ATP + actin + myosin →Actomyosin + Pi + ADP
+ energy
ATPase
• ATP +H2O → ADP + Pi
• ATP then resynthesized by Creatine kinase and
adenylate kinase reactions in immediate energy
systems
• Creatine kinase (CPK) is the
enzyme that releases the
energy stored in PCr to
resynthesize ATP
• The depiction at the R
shows the “creatine
phosphate shuttle”
• Exceptionally small amounts
of stored ATP and PCr (515s)
• These reactions occur in
cytoplasm
Immediate energy systems
• ATP broken down to ADP and Pi
– A buildup of ADP and Pi stimulate metabolism
• A buildup of ADP also inhibits the breakdown of
ATP
• ATP
ADP + Pi
– Thus, Adenylate kinase reaction:
• ADP + ADP
ATP + AMP
– Used during very high energy turnover
Non-oxidative energy sources (continued)
Nonoxidative energy sources
• Glycogenolysis/glycolysis
– Depends on the start point
– Breaks glucose (glycogen)
down to pyruvate
– Pyruvate then converted to
lactate
– Occurs in cytoplasm
– Importance increases for
events lasting longer than
15s and less than a couple
of min.
Oxidative energy sources
Glycolysis→pyruvate
Oxidative energy sources
• Can come from three
primary sources
– Carbohydrate
(glucose/glycogen)
– Fat
– Protein
• Significant stores of fat
• Thus, the body will use
mostly fat at rest
• Complete oxidation of glucose
– C6H12O6 + 6O2 → 6CO2 + 6H2O + 36 ATP
• Complete oxidation of palmitate (16C fatty acid)
– C16H32O2 + 23O2 → 16CO2 + 16H2O + 129 ATP
– And there are 3 fatty acids per molecule of fat (so, 387 ATP)
• Oxidation of amino acids
– Tricky and complicated
– Must be deaminated or transaminated (NH2 group removed or converted to
something else)
Deamination
glutamate
ketoglutarate
Transamination
Capacity of the three energy
systems
• You can see from table
3-5 the inverse
relationship between the
power of the 3 systems
and their capacity
• Important
– All 3 energy systems are
always being used to
some extent, even at rest
Capacity vs Power
Athletic performance
• Note the triphasic
nature of the graph
• Different events may
select out
participants based on
how they store
energy
• Note similarity
between genders
immediate
Non-oxidative
Oxidative
Enzymatic regulation
Enzymatic regulation
•
•
•
•
Substrate: reactant
Active site: where substrate attaches
Enzyme-substrate complex
Conformation
– Can be changed by co-factors (modulators), which
affect enzyme-substrate interaction and rate of reaction
• Modulators (alter the Rx rate)
– Can increase reaction rate (stimulators)
• ADP, AMP, Pi
– Slow reaction rate (inhibitors)
• ATP
Enzymes 2
• Modifaction by modulators called
“allosterism” (bind to specific site and
either inc/dec Rx rate)
– Common allosteric modulators
• Add or remove Phosphate ion (Pi)
– Kinases and phosphatases
• Alters rate of enzymatic reaction
• Vmax: maximum rate of enzymatic
reaction
• KM; Michaleis-Menton constant; substrate
concentration that gives ½ Vmax
Hexokinase: phosphorylates
glucose in muscle
Glucokinase: phosphates glucose
in liver
Changes in energy state
• Note that ATP is
relatively wellmaintained
• PCr begins to get
depleted during
high intensity work
• ADP, AMP, Pi
change as would be
expected from
signals of
intracellular energy
demand
Chapter 4
Basics of metabolism
• Metabolism:
– Sum total of all chemical processes within an
organism; produces heat. Why?
– Metabolic rate: can be measured as heat
production
– O2 consumption provides for almost all of our
metabolic needs, so Vo2 provides a very good
index of metabolic rate
– High Vo2 means high metabolic capacity
Energy transduction
• Conversion of energy from one form to another
– 3 major types of interconversions
• Photosynthesis
• Cellular respiration
• Cell work
– Photosynthesis: plants
• Sunlight + 6 CO2 + 6 H2O → C6H12O6 + 6O2
– Cellular respiration: non-plants
• C6H12O6 + 6O2 → 6CO2 + 6 H2O + energy
– Cell work (ATP used)
• Mechanical, synthetic, chemical, osmotic and electrical
Metabolism and heat production in
animals
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•
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Living animals give off heat
Metabolism is functionally heat production
Calorie: heat required to raise 1 gram water 1 °C
Kilocalorie: what is commonly referred to as a calorie
Calorimetry
• Direct calorimetry
– Place entire animal
in calorimeter
– Measure heat
production
• Indirect calorimetry
– Measure oxygen
consumption
– Easier
Indirect calorimetry
• Simple,
measures Vo2
and Vco2
• Allows work to
be performed
while obtaining
index of
metabolic rate
• Gives a good
index of “fitness”
Steady state
• Note how it takes a while for caloric output to
stabilize during a certain workload
• This stable area is called steady state
• To calculate energy expenditure, steady state
must be achieved
Concept of respiratory
quotient/respiratory exchange ratio
• Ratio of Co2 produced (Vco2) to O2 consumed
(Vo2)
• If measured at the cellular levels: RQ
• If measured at the mouth: RER
• Also RER can go above 1.0, RQ cannot
• Why?
Complete oxidation of glucose
C6H12O6 + 6O2 → 6CO2
+ 6H2O + 36 ATP
Complete oxidation of
palmitate (16C fatty acid)
C16H32O2 + 23O2 →
16CO2 + 16H2O + 129
ATP
Indirect calorimetry
• Couple reasons
– With pure glycolysis, RQ or Vco2/Vo2 is 1.0
– However, when measured at the lung (RER),
additional Co2 production from acid buffering
reactions must be factored in
• Buffering of lactic acid
– HLA↔H+ + La– H+ + HCO3- ↔ H2CO3
– H2CO3 → H2O + CO2
• C6H12O6 + 6O2 ↔ 6H2O + 6CO2
• H+ + HCO3- ↔ H2CO3 → H2O + CO2
• This extra CO2 is called “non-metabolic”
CO2