ch3 - bioenergetics of exercise and training Flashcards
what is catabolism associated with?
release of energy
are exergonic reactions catabolic or anabolic or neither?
catabolic
what do endergonic reactions include?
anabolic processes and the contraction of muscle
through what intermediate molecule are exergonic and endergonic reactions derived?
ATP
what is atp composed of?
adenosine and three phosphate groups
adenosine is the combination of what chemicals?
adenine (a nitrogen-containing base) and ribose (a five-carbon sugar)
the breakdown of one molecule of ATP to yield energy is known as?
hydrolysis, because it requires one molecule of water
what is the hydrolysis of ATP catalyzed by?
an enzyme called adenosine triphosphatase (ATPase)
what is crossbridge recycling?
the process that occurs after myosin ATPase catalyzes ATP hydrolysis
what other enzymes catalyze ATP at other locations?
calcium ATPase for pumping calcium into the sarcoplasmic reticulum, sodium-potassium ATPase for maintaining the sarcolemmal concentration gradient after depolarization
what equation depicts the reactants (left), enzyme (middle), and products (right) of ATP hydrolysis
ATP + H2O ADP + Pi + H+ + Energy
hydrolysis of ADP does what?
cleaves the second phosphate group and yields adenosine monophosphate
how does ATP store energy?
in the chemical bonds of the two terminal phosphate groups, which classifies it as a high-energy molecule
where do ATP-producing processes occur?
in the cell
how does the glycolytic system depend on oxygen?
it doesn’t, neither does the phosphagen system
where do the glycolytic and phosphagenic systems occur?
in the sarcoplasm of a muscle cell
where do the oxidative and aerobic mechanisms occur in muscle cells?
in mitochondria
what do mitochondria require for aerobic mechanisms?
oxygen as the terminal electron acceptor
which of the three macronutrients can be metabolized for energy without oxygen?
carbohydrate, which is critical during anaerobic metabolism
which energy system is active during anaerobic exercise?
all three energy systems are active at any given time, it’s an issue of contribution percentage (modulated by intensity and duration)
what chemical process does the phosphagen system rely on?
hydrolysis of ATP and breakdown of another high-energy phosphate molecule called creatine phosphate (CP), also called phosphocreatine (PCr)
what enzyme catalyzes the synthesis of ATP from CP and ADP?
phosphocreatine / creatine kinase
what is the reaction for catalyzing the synthesis of ATP from CP and ADP?
ADP + CP
what does creatine phosphate do for the ADP–>ATP process
supplies a phosphate group that combines with ADP to replenish ATP, a reaction that provides energy at a high rate
what is the downside of the PCr reaction?
because CP is stored in relatively small amounts, the phosphagen system cannot be the primary supplier of energy for continuous, long-duration activities
how much ATP does the body store?
approximately 80 to 100 g (about 3 ounces) of ATP at any given time, which does not represent a significant energy reserve for exercise
what’s the lowest ATP a body can have?
not zero, because ATP stores cannot be completely depleted due to the necessity for basic cellular function
how much ATP does the body store?
80 to 100 g (about 3 ounces) of ATP at any given time
what are the implications of the amount of stored ATP?
it does not represent a significant energy reserve for exercise, and ATP stores cannot be completely depleted due to the necessity for basic cellular function.
When muscle fatigue causes ATP to be reduced by 50-60% of preexercise levels, how does phosphagen system fix this?
by using the creatine kinase reaction to maintain the concentration of ATP; under normal circumstances, skeletal muscle concentrations of CP are four to six times higher than ATP
which type of muscle fibers contain higher concentrations of CP?
type II, therefore individuals with higher percentages of Type II fibers may be able to replenish ATP faster through the phosphagen system
what is the adenylate kinase reaction?
2ADP ATP + AMP
why is the adenylate kinase reaction important?
because a product of the adenylate kinase (myokinase) reaction is AMP, and AMP is a powerful stimulant of glycolysis
what are the reactions of the phosphagen system controlled by?
the law of mass action / mass action effect
what does the law of mass action / mass action effect control?
the reactions of the phosphagen system
what is a consequence of the phosphagen system having enzyme-mediated reactions?
the rate of product formation is greatly influenced by the concentrations of the reactants
as ATP is hydrolyzed to yield the energy necessary for exercise, there is a transient increase in what?
ADP concentrations (as well as Pi/phosphorus) in the sarcolemma
transient sarcolemma increases in ADP produces what effect?
increases rate of the creatine kinase and adenylate kinase reaction to replenish the ATP supply
for how long will the ATP hydrolysis to increase the rate of ADP concentrations in sarcolemma continue?
the process will continue until (a) the exercise ceases or (b) the intensity is low enough that it does not deplete CP stores and it allows glycolysis or the oxidative system to become the primary supplier of ATP and rephosphorylate the free creatine
after ATP hydrolysis ends and the exercise ceases or glycolysis/oxidative can become primary supplier of ATP (and rephosphorylate the free creatine), what occurs?
the sarcoplasmic concentration of ATP will remain steady or increase, which will slow down or reverse the directions of the creatine kinase and adenylate kinase reactions. as a result, these reactions/equations are often referred to as near-equilibrium reactions that proceed in a direction dictated by the concentrations of the reactants due to the law of mass action
why is the ATP resynthesis rate during glycolysis is not as rapid as with the single-step phosphagen system?
because the process of glycolysis involves multiple enzymatically catalyzed reactions
why is the capacity to produce ATP higher in the glycolytic system than in CP?
due to a larger supply of glycogen and glucose compared to phosphagenic
what is the end result of glycolysis?
pyruvate
what are the two ways pyruvate may proceed?
- Pyruvate can be converted to lactate in the sarcoplasm. 2. Pyruvate can be shuttled into the mitochondria.
how does ATP resynthesis occur at a faster rate when pyruvate is converted into lactate?
via the rapid regeneration of NAD+
what is a limitation of the ATP resynthesis (during pyruvate–>lactate) due to rapid regeneration of NAD+?
limited in duration due to the subsequent H+ production and resulting decrease in cytosolic pH; this process is sometimes called anaerobic glycolysis (or fast glycolysis)
what process is aerobic or slow glycolysis?
when pyruvate is shuttled into the mitochondria to undergo the Krebs cycle, the ATP resynthesis rate is slower because of the numerous reactions, but can occur for a longer duration if the exercise intensity is low enough.
At higher exercise intensities, what happens to pyruvate and NADH?
they will increase above what can be handled by pyruvate dehydrogenase and will then be converted into lactate and NAD+
why might the term aerobic/anaerobic glycolysis be inaccurate?
because glycolysis itself does not depend on oxygen
how do energy demands affect the use of pyruvate?
the fate of pyruvate is ultimately controlled by the energy demands within the cell. if energy demand is high and must be transferred quickly, as during resistance training, pyruvate is primarily converted to lactate for further support of anaerobic glycolysis. if energy demand is not as high and oxygen is present in sufficient quantities in the cell, pyruvate can be further oxidized in the mitochondria.
what catalyzes the formation of lactate from pyruvate?
the enzyme lactate dehydrogenase
what is a mistaken belief about the formation of lactate from pyruvate?
that the end result is the formation of lactic acid.
why is lactate, rather than lactic acid, the product of the lactate dehydrogenase reaction?
due to the physiological pH (i.e., near 7) and earlier steps in glycolysis that consume protons
what are the functions of proton (H+) accumulation during fatigue?
reduces the intracellular pH, inhibits glycolytic reactions, and directly interferes with muscle’s excitation-contraction coupling
how might proton (H+ accumulation interfere with excitation-contraction coupling
possibly by inhibiting calcium binding to troponin or by interfering with crossbridge recycling
how does the decrease in pH affect cell energy systems?
inhibits the enzymatic turnover rate of the cell’s energy systems
what is exercise-induced decrease in pH referred to?
metabolic acidosis, and may be responsible for much of the peripheral fatigue that occurs during exercise, although the role of metabolic acidosis in peripheral fatigue has been questioned recently
what other factors might play a role in peripheral fatigue?
increased interstitial K+ concentration and Pi that impairs Ca++ release
what other mechanisms might be responsible for H+ accumulation?
the simple hydrolysis of ATP
what alternate theory has been posed toward lactate?
that lactate itself actually works to decrease metabolic acidosis rather than accelerate it
how is lactate used as an energy substrate?
in Type I and cardiac muscle fibers and in gluconeogenesis—the formation of glucose from noncarbohydrate sources—during extended exercise and recovery
what is the resting concentration of lactate in blood and in muscle?
normally there is a low concentration of lactate in blood and muscle. The reported normal range of lactate concentration in blood is 0.5 to 2.2 mmol/L at rest and 0.5 to 2.2 mmol for each kilogram of wet muscle (muscle that has not been desiccated).
what factors affect lactate production?
lactate production increases with exercise intensity and appears to depend on muscle fiber type. maximal rate of lactate production for Type II muscle fibers is 0.5 mmol•g−1•s−1 and for Type I muscle is 0.25 mmol•g−1•s−1 (so, type II = double type I)
what might be the reason type II fibers produce so much more lactate than type I?
a higher concentration or activity of glycolytic enzymes than in Type I muscle fibers
what is the highest lactate accumulation, and at what point does severe fatigue occur?
highest possible concentration of lactate accumulation is not known, and severe fatigue may occur at blood concentrations between 20 and 25 mmol/L; another showed blood lactate concentrations greater than 30 mmol/L following multiple bouts of dynamic exercise (so, between 20->30 mmol/L)
what other factors affect lactate accumulation besides exercise intensity and fiber type?
exercise duration, state of training, and initial glycogen levels
what chemical state does blood lactate concentration reflect?
the net balance of lactate production and clearance as a result of bicarbonate (HCO3−) buffering
how does HCO3 − minimize the disruptive influence of H+ on ph?
by accepting the proton (H2CO3)
how do methods of oxidation involve lactate?
lactate can be transported in the blood to other muscle fibers to be oxidized or it can be cleared by oxidation within the muscle fiber in which it was produced
what is a hepatic method to clear lactate, what does it convert to, and what is this called?
lactate can be transported in the blood to the liver, where it is converted to glucose. this process is referred to as the Cori cycle
how long do blood lactate concentrations typically return to preexercise values?
within an hour after activity, depending on the duration and intensity of exercise, training status, and type of recovery (i.e., passive versus active)
what is the effect of light activity on lactate during the postexercise period?
clears lactate faster; light activity during the postexercise period has been shown to increase lactate clearance rates. (for example, an active recovery following a 200-yard (182.9 m) maximal-effort swim resulted in the greatest lactate clearance in comparison to a passive recovery in competitive swimmers. in addition, both aerobically trained and anaerobically trained athletes have faster lactate clearance rates than untrained people.)
when do peak blood concentrations occur?
approximately 5 minutes after the cessation of exercise, a delay frequently attributed to the time required to buffer and transport lactate from the tissue to the blood
given two scenarios: high intensity intermittent and low-intensity continuous, which would result in greater blood lactate accumulation?
greater following high-intensity, intermittent exercise (e.g. resistance training, sprinting) than following lower-intensity, continuous exercise
how would you infer that resistance training results in alterations of lactate response similar to those from aerobic training?
trained people experience lower blood lactate concentrations than untrained people when exercising at an absolute workload (same resistance); these alterations include (1) lower blood lactate concentration at a given workload in trained individuals (2) higher blood lactate concentrations in trained individuals during maximal exercise
what is the net reaction for glycolysis when pyruvate is converted to lactate?
Glucose + 2Pi + 2ADP –> 2Lactate + 2ATP + H2O
when would pyruvate not be converted into lactate?
when oxygen is present in sufficient quantities in the mitochondria; pyrvuate is then transported there along with two molecules of reduced nicotinamide adenine dinucleotide (NADH) produced during glycolytic reactions (reduced refers to the added hydrogen)
how does acetyl coenzyme A enter mitochondria?
from pyruvate, which converts to acetyl CoA through the pyruvate dehydrogenase complex
what is a consequence of the pyruvate –> acetyl CoA conversion?
the loss of a carbon as CO2, and acetyl-CoA can then enter the Krebs cycle for further ATP resynthesis
what happens after acetyl CoA enters the Krebs cycle?
the NADH (nicotinamide adenine dinucleotide) molecules enter the electron transport system, where they can also be used to resynthesize ATP
the net reaction for glycolysis when pyruvate is shuttled to the mitochondria may be summarized as what?
Glucose + 2Pi + 2ADP + 2NAD+ –> 2Pyruvate + 2ATP + 2NADH + 2H2O
what are the two primary mechanisms for resynthesizing ATP during metabolism?
- Substrate-level phosphorylation 2. Oxidative phosphorylation
what is phosphorylation?
the process of adding an inorganic phosphate (Pi) to another molecule
ADP + Pi –> ATP is what?
the phosphorylation of ADP to ATP
the resynthesis of ATP in the electron transport chain is also called what?
oxidative phosphorylation
substrate-level phosphorylation refers to what?
direct resynthesis of ATP from ADP during a single reaction in the metabolic pathways.
in glycolysis, what are the two steps that result in substrate-level phosphorylation of ADP to ATP?
I. 1,3-bisphosphoglycerate + ADP + Pi phosphoglycerate kinase –> 3-phosphoglycerate + ATP II. Phosphoenolpyruvate + ADP + Pi + Pyruvate kinase—> Pyruvate + ATP
what is the gross number of ATP molecules that are resynthesized as a result of substrate-level phosphorylation during glycolysis?
four
in glycolysis, the reaction that converts fructose-6-phosphate to fructose-1,6-bisphosphate is catalyzed by what?
the enzyme phosphofructokinase [PFK]
in glycolysis, what is required for the reaction that converts fructose-6-phosphate to fructose-1,6-bisphosphate to occur?
the hydrolysis of one ATP molecule.
in glycolysis, what are the two possible sources of glucose?
blood glucose and muscle glycogen
what are the requirements for when blood glucose enters the muscle cell?
- it must be phosphorylated to remain in the cell and to maintain the glucose concentration gradient 2. the phosphorylation of one molecule of blood glucose, which is catalyzed by hexokinase, also requires the hydrolysis of one ATP
