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+ BIOL 370 > Lecture 9.1 and 9.2: Muscle Energy Metabolism > Flashcards

Lecture 9.1 and 9.2: Muscle Energy Metabolism Flashcards

1
Q

Energy Transfer

Moving System Toward vs. Away From Equilibrium

A
  • move system toward equilibrium: energy is produced
  • move system away from equilibrium: energy is required (work)
  • low thermodynamic stability in products and reactants
  • high thermodynamic stability (lower energy) at equilibrium
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2
Q

Steady State Conditions

A → B

A
  • there is a way to replenish ‘A’ at the same rate it is converted to ‘B’
  • there is a way to remove ‘B’ at the same rate it is produced from ‘A’
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3
Q

In living cells, do reactions ever ‘finish’?

A

no – kept from reaching equilibrium

  • reactions are always at some point away from equilibrium, but moving towards equilibrium
  • if equilibrium is reached, cell dies
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4
Q

ATP Hydrolysis

ATP + H2O → ADP + Pi + H+

A
  • amount of energy is proportional to the difference in thermodynamic stability of all reactants and all products
  • hydrolysis products are more strongly bonded than reactants
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5
Q

ATP Hydrolysis

What is resonance stabilization?

A

there is greater resonance stabilization in products than reactants

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6
Q

ATP Hydrolysis

What are charge repulsion effects?

A

there is more ‘bond weakening’ by charge effects in reactants than in products

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7
Q

What are the 2 mechanisms through which ATP is generated?

A
  • substrate level phosphorylation (SLP)
  • oxidative phosphorylation (Ox Phos)
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8
Q

What are the 3 main substrates used for substrate level phosphorylation (SLP)?

A
  • creatine phosphate
  • glucose/glycogen
  • lipid
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9
Q

How is ATP generated via SLP with creatine phosphate?

A

ATP generated via removal of phosphate, which can then be used in muscle contraction

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10
Q

How is ATP generated via SLP with glucose/glycogen?

A

ATP generated via oxidation

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11
Q

How is ATP generated via SLP with lipids?

A

ATP generated via oxidation

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12
Q

Describe the ATP yield for glucose oxidation.

A

glucose is converted into 2 pyruvate via glycolysis in cell cytosol

  • produces 2 ATP
  • substrate level phosphorylation

pyruvate is converted into 2 acetyl-CoA in mitochondrial matrix

  • acetyl-CoA enters TCA cycle and produces 2 ATP
  • substrate level phosphorylation (pyruvate is phosphorylated)

other products of glycolysis are used in electron transport in mitochondrial inner membrane

  • produces various amounts of ATP
  • oxidative phosphorylation
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13
Q

What is the actual vs. theoretical yield for glucose oxidation? Why?

A

actual ATP yield (32) is lower than the theoretical yield (36) due to involvement of H+ in pyruvate and ADP transport

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14
Q

Amount of Available Substrate in White Muscle (Fast Contraction)

A

creatine phosphate > glycogen > lipid > ATP > glucose

  • ATP: muscle [ATP] = < 5 mmol/kg
  • creatine phosphate: muscle [CrP] = around 40 to 50 mmol/kg
  • glucose/glycogen: muscle glucose = 2 mmol/kg, muscle glycogen = 25 to 30 mmol/kg
  • lipid: muscle triacylglycerol = 20 mmol/kg
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15
Q

Where are the sources of the main substrates that support ATP production?

A

muscles have stored sources for ATP production, or sources get transported through blood to muscle tissue

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16
Q

Source of Main Substrates that Support ATP Production

Where are carbohydrate sources?

A
  • glucose from muscle stores of glycogen – main store
  • glucose from blood
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17
Q

Source of Main Substrates that Support ATP Production

Where are lipid sources?

A
  • fatty acids are stored in muscle and adipose tissues as triacylglycerol
  • fatty acids from lipoproteins from the blood
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18
Q

What does mitochondrial beta-oxidation do?

A

breaks fatty acids into 2 carbon acetyl-CoA, which enter TCA and produce ATP

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19
Q

What substrate does glycolysis use?

A

only carbohydrates

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20
Q

What substrate does oxidative phosphorylation use?

A

can oxidize carbohydrates or lipids (or amino acids)

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21
Q

Carbohydrates vs. Lipids

Which substrate can be more rapidly mobilized?

A

glycogen

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22
Q

Carbohydrates vs. Lipids

Which substrate is a more dense source of energy?

A

lipids

  • cell can produce approximately 10x more ATP from triglyceride droplets than from the same volume of glycogen granules
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23
Q

Carbohydrates vs. Lipids

Which substrate is associated with mitochondria?

A
  • triglyceride droplets are always associated with mitochondria
  • only some glycogen granules are associated with mitochondria, while others are dispersed within myofibrils
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24
Q

Carbohydrate Pathway: How are carbohydrates converted into ATP?

A
  1. glycogen is broken down into glucose 1-P by glycogen phosphorylase
  2. glucose 1-P is converted into pyruvate via glycolysis and yields ATP
  3. pyruvate is transported into mitochondria
  • pyruvate dehydrogenase converts pyruvate into acetyl-CoA
  • pyruvate may also sometimes be converted into lactate
  1. acetyl-CoA enters TCA cycle, which yields electrons that are used in oxidative phosphorylation to make ATP that is used in muscle contraction
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25
Q

Phosphocreatine Pathway: How is phosphocreatine converted into ATP?

A
  1. converted into creatine
  2. generates ATP molecule that can be used for muscle contraction
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26
Q

Lipid Pathway: How are lipids converted into ATP?

A
  1. fatty acids can be transported to mitochondria with the help of carnitine
  2. beta-oxidation produces acetyl-CoA
  3. acetyl-CoA enters TCA cycle, which yields electrons that are used in oxidative phosphorylation to make ATP that is used in muscle contraction
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27
Q

Which substrate pathway is used during physical activity?

A

all three pathways are often used in combination to meet the energy demands of varying exercise intensities and durations

  • choice of which pathway predominates depends on the specific requirements of the exercise and the availability of substrates and oxygen
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28
Q

What are the sources of acetyl-CoA production during muscle metabolism?

A

carbohydrates, fatty acids, and amino acids

  • amino acids can be converted into pyruvate and then acetyl-CoA, OR can be converted directly into acetyl-CoA and be used as a source during muscle metabolism – depends on type and duration of exercise, etc. which determines which pathway is used
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29
Q

What are the advantages of phosphocreatine hydrolysis to replenish ATP during muscle activity?

A
  • speed – provides rapid energy for short bursts of high-intensity exercise
  • anaerobic – no oxygen requirement
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30
Q

What are the disadvantages of using glycolysis to replenish ATP during muscle activity?

A
  • inefficient ATP production
  • lactic acid production/muscle soreness
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31
Q

What are the advantages of using oxidative phosphorylation to replenish ATP during muscle activity?

A
  • efficiency in ATP production/extended period of time/no lactic acid production
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32
Q

What are the 3 main categories of enzymes?

A
  • near equilibrium
  • allosteric
  • flux generating
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33
Q

What are near equilibrium enzymes?

A
  • obeys Michaelis-Menten kinetics
  • operates a near equilibrium
  • high muscle enzyme concentration and kcat
  • small changes in substrate concentration ( [P]/[S] ) affects flux through enzyme
  • ie. aldolase
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34
Q

What are allosteric enzymes?

A
  • classic sigmoidal shape
  • operates far from equilibrium
  • lower enzyme concentration in muscle tissue
  • binding of +/- modulators to enzyme at sites other than active sites affect enzyme function – affects relationship between [S] and VO, shifts sigmoidal curve
  • ie. phosphofructokinase, hexokinase
35
Q

When are hexokinase and phosphofructokinase allosterically regulated?

A

in the preparatory phase of glycolysis

36
Q

What does phosphofructokinase do?

A

catalyzes phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate (in glycolysis)

37
Q

What are the positive and negative regulators of phosphofructokinase?

A
  • positive regulators: binding AMP and ADP, fructose 2,6-bisphosphate when cell is in low energy level
  • negative regulators: ATP, citrate
38
Q

What does hexokinase do?

A

catalyzes phosphorylation of glucose by ATP to glucose-6-P (in glycolysis)

39
Q

What are flux generating enzymes?

A
  • operates in an ‘on/off’ type fashion
  • operates far from equilibrium
  • very low enzyme concentration
  • post-translational modification (ie. phosphorylation/dephosphorylation) transitions enzyme from on and off state
  • ie. pyruvate dehydrogenase
40
Q

What are the two main steps in ATP pathways that are controlled by flux generating enzymes?

A
  • glycogen breakdown/synthesis
  • pyruvate to acetyl-CoA
41
Q

What does glycogen synthase do?
What is it stimulated and inhibited by?

A

converts glucose 1-P into glycogen

  • stimulated by dephosphorylation – insulin activates protein phosphatase, which dephosphorylates glycogen synthase and stimulates glycogen synthesis
  • inhibited by phosphorylation – glucagon and epinephrine increase the cAMP levels, which activates protein kinase A, which phosphorylates glycogen synthase and inhibits glycogen synthesis
42
Q

What does glycogen phosphorylase do?
What is it stimulated and inhibited by?

A

converts glycogen into glucose 1-P

  • stimulated by glucagon and epinephrine
  • inhibited by insulin
43
Q

What does pyruvate dehydrogenase do?

A

forms acetyl-CoA from pyruvate

44
Q

What regulates pyruvate dehydrogenase?

A

two other enzymes

  • PDH phosphatase: removes phosphate, results in high PDH enzyme activity
  • PDH kinase: adds phosphate, results in low PDH enzyme activity
45
Q

What is the main factor that causes activation of pyruvate dehydrogenase upon initiation of muscle contraction?

A

Ca2+

  • Ca2+ is released from SR, high concentration in muscle cells
  • Ca2+ activates PDH phosphatase
46
Q

High-Intensity Exercise – Rainbow Trout

What muscles power intense exercise in rainbow trout?

A

white, type IIb muscle (fast twitch, fast contraction)

47
Q

High-Intensity Exercise – Rainbow Trout

What does very intense exercise result in?

A
  • decreases in white muscle [ATP], [creatine phosphate], and glycogen
  • increases in lactate to high levels, and small increases in other glycolytic intermediates (pyruvate)
48
Q

High-Intensity Exercise – Rainbow Trout

What is their exercise fuel?

A
  • first 10 seconds of intense exercise is fueled around 50:50 with CrP hydrolysis and glycolysis
  • glycolysis contributes to ATP production throughout the bout of intense exercise
  • oxidative phosphorylation also contributes to a small degree, and peaks later
49
Q

High-Intensity Exercise – Rainbow Trout

What is glycogen phosphorylase (PHOSa)?

A

enzyme that breaks down glycogen to glucose 1-P

  • activated very quickly during intense exercise
50
Q

High-Intensity Exercise – Rainbow Trout

What is pyruvate dehydrogenase (PDHa)?

A

enzyme that converts pyruvate to acetyl-CoA in mitochondria

  • slow to activate during intense exercise
51
Q

High-Intensity Exercise – Rainbow Trout

There is a difference in rate/regulation between glycogen phosphorylase (PHOSa) and pyruvate dehydrogenase (PDHa). What does this cause?

A

results in lactate accumulation in white muscle

  • PDH is slow to activate during intense exercise
  • mitochondrial content, and therefore PDH capacity, are low in white muscle
  • white muscle (~2% mitochondria)
  • red muscle (~20% mitochondria)
52
Q

High-Intensity Exercise – Rainbow Trout

Is white muscle limited in O2 during intense ‘so-called anaerobic’ exercise?

A
  • mitochondria from white muscle becomes progressively oxidized (higher NAD+) over the course of exhaustive exercise
  • NADH can only be oxidized by the mitochondria via functioning electron transfer system, with the terminal electron acceptor O2

O2 is available for mitochondria during intense exercise

  • indicated by the fact that NAD+/NADH ratio is increasing over time consistently – more NAD means there is no limit of oxygen
  • limitation of oxygen is NOT an issue
52
Q

High-Intensity Exercise – Fish vs. Humans

In both trout and humans, what is high-intensity exercise fueled by?

A
  • initially by PCr hydrolysis and glycolysis (yielding lactate)
  • glycolysis supports ATP production throughout
  • contributions from oxidative phosphorylation increase over time
53
Q

High-Intensity Exercise – Rainbow Trout

What causes lactate accumulation in white muscle during intense exercise?

A

due to metabolic inertia

  • PHOS is fast to activate allowing glucose to enter glycolysis
  • PDH is slow to activate, but does fully activate and supply acetyl-CoA to an oxygenated mitochondria
  • mitochondrial content is low in white muscle
  • the only option to allow continued functioning of glycolysis is for lactate to be produced
54
Q

High-Intensity Exercise – Fish vs. Humans

What generates ATP the fastest?

A

PCr can generate ATP the fastest at nearly 2.5 mmol/kg/s

  • want this in fast twitch muscle
55
Q

High-Intensity Exercise – Fish vs. Humans

What generates ATP the slowest?

A

fat oxidation generates ATP the slowest

  • explains why fat is not really a source of ATP here
56
Q

High-Intensity Exercise

How does cellular pH change?

A

white muscle becomes acidotic during intense exercise – many studies have demonstrated an association between lactate accumulation and acidosis

57
Q

High-Intensity Exercise

What might be the cause of acidosis in muscle?

A

lactic acid is produced when lactate reacts with H+, which is very acidic – can explain acidosis in muscle

source of H+:

  • X generation of ATP via creatine phosphate consumes H+
  • X glycolysis produces H+, but they are balanced throughout the reaction (not available)
  • ✓ ATP hydrolysis
58
Q

High-Intensity Exercise

How is ATP hydrolysis the source of H+ contributing to acidosis in muscle?

A
  • ATP hydrolysis (which supports muscle during high-intensity exercise) is the main source of metabolic acid
  • during high-intensity exercise, rate of ATP hydrolysis to support cellular work exceeds the capacity of mitochondrial oxidative phosphorylation
  • produced much faster than can be used
  • ADP and Pi from ATP hydrolysis are recycled during ATP production via glycolysis but the accumulation of H+ is not, resulting in acidosis
59
Q

High-Intensity Exercise

Why doesn’t the cell become acidotic during low-intensity exercise?

A

because ATP is hydrolyzed at appreciable rates during ‘aerobic’ exercise

  • no accumulation of H+ or Pi
60
Q

Recovery from High-Intensity Exercise

What occurs during recovery?

A
  • replenish energy stores – ATP, phosphocreatine, glycogen
  • re-establish ion gradients, Ca2+ stores, and pH
  • these aspects of recovery are achieved using ATP produced by oxidative phosphorylation
61
Q

Recovery from High-Intensity Exercise

Describe how the rate of oxygen consumption changes during and after exercise.

A
  • exercise causes a rapid increase in the rate of oxygen consumption
  • once exercise stops, respiration declines but remains elevated above the resting rate for extended periods
  • duration of this elevated post-exercise oxygen consumption (oxygen debt) depends on intensity of exercise, and varies among species
62
Q

Recovery from High-Intensity Exercise – Rainbow Trout

What happens during recovery in white muscle?

A
  • creatine phosphate (CrP) recovers very quickly
  • ATP takes 2-4 hrs to recover
  • glycogen is very slow to recover
  • lactate recovers between 2-4 hrs
63
Q

Recovery from High-Intensity Exercise – Rainbow Trout

What are the two possible options of where ATP comes from to support recovery from intense exercise?

A
  • X lactate → pyruvate → oxidative phosphorylation
  • ✓ lipids
64
Q

Recovery from High-Intensity Exercise – Rainbow Trout

Explain why ATP does NOT come from lactate → pyruvate → oxidative to support recovery.

A
  • immediately upon completing high-intensity exercise, glycogen synthase is 80% activated and remains activated for 8 hrs post-exercise
  • pyruvate dehydrogenase is high immediately post-exercise, but is inactivated within 15 mins of recovery
  • intramuscular lactate is converted into pyruvate and shuttled toward glycogen synthesis by inactivation of PDH – this means that the source of ATP cannot come from lactate
65
Q

Recovery from High-Intensity Exercise – Rainbow Trout

Explain why ATP comes from lipids to support recovery.

A
  • during recovery there is an increase in white muscle acetyl-CoA
  • rapid inactivation of white muscle PDH during recovery shuttles lactate toward glycogen synthesis – lactate is therefore not oxidized during recovery to generate ATP, meaning that the source of acetyl-CoA cannot be lactate or pyruvate

immediately post-exercise, the increase in white muscle acetyl-CoA comes from digestion of lipids and fatty acids

  • free carnitine in the white muscle decreases during the early part of recovery, suggesting that they may be used for fatty acid transport
  • long-chain fatty acyl carnitine (and acetyl-carnitine) accumulate, suggesting higher fat transport into the mitochondria during recovery
  • could explain the level of acetyl-CoA and PDH being inactivated
66
Q

Recovery from High-Intensity Exercise – Rainbow Trout

How is lactate removed?

A
  • some muscles can convert lactate to glucose to replenish glycogen stores
  • other muscles release lactate into the blood which transports it to the liver or oxidative tissues such as the heart
  • glucose taken up from the blood is used to replenish muscle glycogen stores
67
Q

Recovery from High-Intensity Exercise – Rainbow Trout

How does the liver remove lactate?

A

converts lactate to glucose (gluconeogenesis) – some of this glucose can be shuttled back towards to Cori cycle for further generation of glycogen

68
Q

Recovery from High-Intensity Exercise – Rainbow Trout

How do oxidative tissues (such as the heart) remove lactate?

A

oxidize lactate to produce ATP

69
Q

What is graded exercise?

A

exercise that starts slowly and gradually increases over time

70
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

Describe speed.

A
  • Ucrit = maximal ‘sustained’ swimming speed
  • speed increases over time, but there are periods of fatigue in between each increase in speed
  • electric potential being generated in muscle tissue for both red (sigmoidal) and white (exponential) muscle increases as Ucrit increases
71
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

At what speeds could swimming be sustained for long periods of time? How?

A

swimming under control conditions and at 30 and 60% Ucrit are sustainable for long periods of time

  • supported by O2 based metabolism – oxygen consumption increased over time
72
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

At what speeds were fish unable to sustain swimming for long periods of time?

A

swimming at 90% Ucrit only lasted for between 50 and 80 min, and then they were exhausted

73
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

What can ‘aerobic’ ATP turnover be calculated from?

A

can be calculated from O2 update rate

  • O2 consumption increases with increase in Ucrit
  • ADP:O2 ratio of 6
74
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

Describe white muscle changes.

A
  • good for short bursts of fast swimming
  • at 90% Ucrit, white muscle ATP, CrP, and glycogen are depleted, and lactate accumulates
  • very limited changes in white muscle metabolites during swimming at 30 and 60% Ucrit
75
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

Describe red muscle changes.

A
  • red muscle [ATP] does not change during submaximal exercise
  • CrP is depleted in red muscle at 90% Ucrit initially, but stabilized during swimming
  • remember steady state functioning of metabolism: lack of change in [ATP] and [CrP] during ongoing swimming does not mean there is no change in flux through pathways associated with ATP and CrP production and consumption – being used at the same rate as it is being replenished
  • red muscle glycogen depleted in fish at 90% Ucrit, with lactate accumulation
  • almost no changes in red muscle glycogen and lactate over 240 min swimming at 30 and 60% Ucrit
76
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

Red Muscle – When is pyruvate dehydrogenase activated?

A

activated early at all swimming speeds

  • within 15 min swimming at 30 and 60% Ucrit, PDH is inactivated
  • PDH remains active throughout 45 min of swimming at 90% Ucrit
  • explains glycogen is being used as a source, and is being shuttled towards acetyl-CoA and TCA cycle, especially at higher speeds
77
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

Red Muscle – What accumulates in red muscle? What is the source?

A

acetyl groups accumulate in red muscle in trout swimming at 60 and 90% Ucrit

  • amount of free carnitine is decreasing, while the amount of carnitine-conjugated fatty acids is increasing, suggesting that more lipids are being transported to the mitochondria, which could explain the increased level of acetyl-CoA
78
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

Red Muscle – How can the beta-oxidation pathway be kept ‘on’ during swimming to provide acetyl-CoA?

A

malonyl-CoA: allosteric inhibitor of carnitine palmitoyl transferase (CPT1)

  • concentration decreases in red muscle during swimming at all speeds
  • if you inhibit and inhibitor, the pathway continues – CPT1 remains activated, therefore more lipids can be transported to the mitochondria via carnitine to be used during beta-oxidation to provide more acetyl-CoA
79
Q

Graded Exercise – Fish Treadmill (Swim Tunnel)

What fuels red muscle?

A
  • swimming at 30 and 60% Ucrit is initially fueled by carbohydrate oxidation (2 min), but then by lipids – (source of lipids (plasma fatty acid/muscle TAG) is unknown)
  • as swimming speed increases (ie. 90% Ucrit), muscle glycogen contributes more substantially to support muscle contraction
  • at different speeds, different fuels are functioning
  • similar effects of running speed on human oxidation
80
Q

Hummingbirds

What do hummingbirds require to support their metabolic rate?

A

high caloric intake

81
Q

Hummingbirds

What is the source of food mainly used during hovering flight?

A

carbohydrates/sugar

  • ingested sugar from nectar is used to support flight muscle metabolism
82
Q

Hummingbirds

What is the source of food mainly used during rest periods?

A

lipids

83
Q

What is a respiratory quotient (ratio)?

A

volume of CO2 released over the volume of O2 absorbed during respiration

  • amount of O2 consumed by an animal compared with the amount of CO2 produced can tell us something about the fuels that are used
  • amount of O2 used and CO2 produced is different when using carbohydrates vs. lipids
  • around 0.7 = lipid
  • around 1.0 = carbohydrate

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