Chapter 3/4: Bioenergetics and Exercise Metabolism Flashcards
1 g of carbohydrates yields
4 kcal of energy
1 g of fat yields
9.5 kcal of energy
1 g of protein yields
4 kcal of energy
storage form and location for carbohydrates
glycogen in the liver & muscle
define glycogenesis. performed by what enzyme?
synthesis of glycogen by glycogen synthase
define glycogenolysis. performed by what enzyme?
breakdown of glycogen to glucose by glycogen phosphorylase
define gluconeogenesis
synthesis of glucose from non-carb sources (e.g. amino acids or lactate)
define glycolysis
breakdown of glucose to pyruvate or lactate; mediated by the rate-limiting enzyme phosphofructose kinase
storage form and location for fats
stored as triglycerides in muscle and adipose tissue
define lipogenesis
synthesis of triglycerides from glycerol and free fatty acids
define lipolysis. performed by what enzyme?
breakdown of triglycerides into glycerol and free fatty acids by lipases
which component of triglycerides is not an important muscle fuel during exercise?
glycerol
define beta-oxidation
breakdown of free fatty acids to acetyl coA, which then enters the Krebs cycle
when are proteins used as an energy source?
extreme endurance races or starvation
how are proteins used as an energy source?
muscles can directly metabolize branch chain amino acids and alanine; the liver can convert alanine to glucose
define lactate shuttle
lactate produced in one tissue and transported to another is converted to acetyl-CoA and enters the Krebs cycle
define Cori cycle
lactate can be converted to glucose in the liver
how much ATP do we have in storage?
store only small amounts (~100 g) until needed; body must constantly synthesize new ATP
does the synthesis of ATP require oxygen
can occur in the presence or absence of oxygen
formula for the synthesis of ATP
ADP + Pi + energy —> ATP
formula for the breakdown of ATP
ATP + water (ATPase) —> ADP + Pi + energy
3 ATP synthesis pathways
1) ATP-PC system
2) glycolysis
3) oxidative phosphorylation
does the ATP-PC system require oxygen
no; anaerobic
ATP yield of the ATP-PC system
1 mol ATP / 1 mol phosphocreatine
duration (of energy) provided by the ATP-PC system
1-5 sec of maximal exercise (striking matches)
when is the ATP-PC pathway used
used to reassemble ATP because ATP stores are limited
what can phosphocreatine NOT be used for? what can it be used for?
PC cannot be used for cellular work, but it can be used to reassemble ATP
what does the ATP-PC system provide energy for
muscular contraction at the onset of exercise and during short-term, maximal exercise
does glycolysis need oxygen?
no; anaerobic
ATP yield of glycolysis
2-3 mol ATP / 1 mol substrate
duration (of energy) for glycolysis ?
intense exercise longer than 5 seconds
substrate and products of glycolysis
breakdown of glucose to 2 pyruvic acid or 2 lactic acid
what is the difference between using glucose and glycogen as the substrate for glycolysis?
if you use glucose, you must convert it to glucose-6-phosphate, which requires the input of 1 ATP
if you use glycogen, the phosphate is already present on the glucose and doesn’t require any ATP input
where does glycolysis occur
cytoplasm
rate limiting enzyme for glycolysis
phosphofructose kinase
pros of glycolysis
allows muscles to contract with limited O2, permits shorter term, higher-intensity exercise (up to 45 sec) than oxidative metabolism can sustain (because it is much faster)
cons of glycolysis
low ATP yield, inefficient use of substrate, lack of O2 converts pyruvate acid to lactic acid which increase H+ conc. and impairs glycolysis and muscle contraction
why is pyruvate converted to lactate at the end of glycolysis?
the conversion of pyruvate to lactic acid converts one NADH to NAD+ which allows glycolysis to continue (also donates H+ to pyruvate to make lactic acid)
what happens to lactic acid immediately?
dissociates into lactate and H+, which changes pH
does oxidative phosphorylation require oxygen
yes, aerobic
ATP yield of oxidative phosphorylation
depends on the substrate
32 ATP/ glucose
33 ATP / glycogen
100+ ATP / 1 FFA
duration (of energy) provided by oxidative phosphorylation
steady supply for hours
where does oxidative phosphorylation occur
mitochondria
3 steps of oxidation of carbohydrates
1) glycolysis
2) Krebs cycle
3) electron transport chain
what is the energy yield of the Krebs cycle? for one molecule of glucose?
3 NADH, 1 FADH2, 1 GTP
but runs through 2 acetyl-coA so 6 NADH, 2 FADH2, 2 GTP
energy equivalents of NADH and FADH2
2.5 ATP per NADH
1.5 ATP per FADH2
how does the electron transport chain generate ATP?
H+ carried to electron transport chain via NADH and FADH molecules, where H+ electrons travel down the chain creating a conc. gradient, H+ combines with O2 to form H2O; conc gradient is used to make ATP
energy breakdown of oxidation of a carbohydrate
glycolysis: +2 or +3 ATP
GTP from Krebs: +2 ATP
10 NADH = +25 ATP
2 FADH = +3 ATP
which is faster, oxidation of fat or oxidation of carbs?
oxidation of carbs
beta-oxidation substrates and products
converts free fatty acids to acetyl-coA so that it can enter the Krebs cycle
how much ATP does B-oxidation cost?
2 ATP
does oxidation of fats or oxidation of carbs require more oxygen?
oxidation of fats
how many ATP are generated per B-oxidation cycle?
14 ATP
how to calculate net yield of ATP from beta oxidation of a free fatty acid
total ATP = (n-1)*14 + 10 - 2
where n = number of acetyl CoA molecules
list the energy systems in order of fastest rate of ATP generation to slowest rate of ATP generation
ATP-PC, glycolysis, CHO oxidation, fat oxidation
list the energy systems in order of most maximal available energy to least maximal available energy
fat oxidation, CHO oxidation, glycolysis, ATP-PC
formula for respiratory exchange rate (RER)
what conditions have to be met for this formula to be used?
R = volume of CO2 produced / volume of O2 consumed
subject must have reached steady state
R for fat
= 16 CO2/ 23 O2 = 0.70
R for carbohydrate
= 6 CO2/ 6 O2= 1.00
is it physiologically possible for R to be outside the range 0.70-1.00?
yes, VO2 will not change but VCO2 can change if the body uses the bicarbonate buffering reaction to create CO2
during the rest-to exercise transition, what pathways initially produces ATP?
ATP-PC system and glycolysis
how quickly does oxygen uptake reach steady state? what pathway of ATP production is used once steady state is reached?
1-4 minutes; aerobic ATP production
what is the oxygen deficit?
lag in oxygen uptake at the beginning of exercise; O2 demand > O2 consumed
how does training change the oxygen deficit?
faster rise in VO2 curve and steady state is reached earlier; energy requirement can be met by oxidative ATP production at the onset of exercise
what does having a lower oxygen deficit result in?
less lactate and H+ formation & less PC depletion
what kind of energy systems contribute more during short-term, high-intensity activities?
anaerobic energy systems (ATP-PC and glycolysis)
what kind of energy systems contribute more during long-term, low-intensity exercise?
aerobic energy systems (oxidative phosphorylation)
where does energy come from during the first 1-5 seconds of short-term, high-intensity exercise?
ATP-PC system
where does energy come from after 5 seconds during short-term, high-intensity exercise?
shifts to ATP production via glycolysis
where does energy come from when an event last longer than 45 seconds during short-term, high-intensity exercise?
ATP production through ATP-PC, glycolysis, and aerobic systems
percent contribution of aerobic/anaerobic sources at 60 seconds of short-term, high-intensity exercise?
70% anaerobic, 30% aerobic
percent contribution of aerobic/anaerobic sources at 2-3 mins of short-term, high-intensity exercise?
50% anaerobic, 50% aerobic
where does energy come from during prolonged exercise (> 10 mins) in a cool environment?
primarily aerobic metabolism, steady state oxygen uptake can generally be maintained during submaximal exercise (below lactate threshold)
describe the concept of upward drift
there is an upward drift in oxygen uptake over time in hot and humid environments, steady state is not obtained
what is upward drift due to?
rising body temp, and increasing Epi and NE
during prolonged, low intensity exercise, how does fuel selection change?
shift from CHO metabolism to fat metabolism
why does fuel selection shift towards fats during prolonged, low-intensity exercise?
increased rate of lipolysis via lipases which is stimulated by rising levels of Epi
during prolonged exercise at the same intensity, how does fuel utilization of trained athletes differ from those less fit?
trained athletes use more fat and less CHO
during graded exercise, what energy source is primarily used?
ATP production primarily from aerobic metabolism
how does oxygen uptake change during a graded exercise with increasing work rate?
oxygen uptake increases linearly until VO2 max is reached
what is VO2 max? what is it influenced by?
“physiological ceiling” for delivery of O2 to muscles; influenced by genetics and training
2 physiological factors influencing VO2 max
1) maximum ability of cardiorespiratory system to deliver oxygen to the muscle
2) ability of muscles to use oxygen to produce ATP aerobically
what is the primary fuel for low intensity exercise (<30% VO2 max)?
fats
what is the primary fuel used for high-intensity exercise (>70% VO2 max)?
carbs
describe the crossover concept
the shift from fat to carb metabolism as exercise intensity increases
why does the crossover concept happen?
1) recruitment of fast muscle fibers that are better equipped to metabolize carbs than fats
2) increasing blood levels of Epi stimulate glycogenolysis
how does training affect the crossover concept?
increases utilization of fat and sparing of plasma glucose and muscle glycogen (crossover shifts right)
what is the lactate threshold?
work rate at which blood lactic acid rises systematically during graded exercise
where does the lactate threshold appear for untrained subjects?
50-60% VO2 max
where does the lactate threshold appear for trained subjects?
65-85% VO2 max
what may contribute to the sudden increase in blood lactate levels?
accelerated glycolysis, recruitment of fast-twitch fibers, and reduced rate of lactate removal
how is lactate threshold useful in planning training programs?
training near (just below) lactate threshold is effective in shifting the lactate threshold to the right
how can you use lactate threshold to estimate a 10k race time?
1) plot blood lactate vs VO2, determine VO2 at Lactate threshold
2) plot VO2 vs running speed, determine speed at lactate threshold
3) race pace at 5 m/min above LT
4) 10k time (min) = 10,000m/ (speed at LT m/min + 5 m/min)
what is the underlying issue in McArdle’s disease
cannot synthesize enzyme glycogen phosphorylase, inability to breakdown muscle glycogen
do lactate levels rise in McArdle’s patients?
no
why can’t McArdle’s patients oxidize more fat?
reduced rate of glycolysis —> reduced production of pyruvate —> reduced Krebs cycle intermediates —> reduced fat oxidation
when is the highest rate of fat oxidation reached?
just before lactate threshold
what is excess post-exercise oxygen consumption (EPOC)
O2 consumed > O2 demand
factors contributing to the rapid portion of EPOC
resynthesis of PC in muscle & restoration of muscle and blood oxygen stores
factors contributing to the slow portion of EPOC
lactate conversion to glucose, elevated body temp, post-exercise elevation of HR and breathing, elevated hormones
