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Exercise Nutrition > Energy Expenditure > Flashcards

Energy Expenditure Flashcards

1
Q

Sarcomeres

  • What are sarcomeres
  • Striations
  • Z discs
  • M line
A

What are sarcomeres

  • Smallest contractile unit or segment of muscle fibre, extends between 2 z-lines.
  • Actin - thin
  • Myosin - thick

Striations
- Myofibrils give the striated appearance under the microscope

Z discs
- The line that defines the borders of 2 sarcomere units

M line:

  • The attachment site for the thick filaments (myosin)
  • The centre of the sarcomere
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2
Q

Myosin & Actin

A

Myosin

  • Breakdown of ATP to ADP and inorganic phosphate by the myosin - ATPase provides the energy for muscle contraction
  • ATP binds to the myosin
Actin 
- Myosin binding site
-  Tropomyosin – covers myosin binding site (until ready for contraction)
- Troponin: 
    * 3 subunits: 
        \+ Binds to calcium 
        \+ Binds to actin 
        \+ Binds to tropomyosin
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3
Q

Muscle Contraction

A
  • Electrical excitation (action potential - along cell membrane (sarcolemma) down t-tubules
  • When there is sufficient ATP and calcium, actin and myosin attach forming actomyosin and then release pulling towards the M line
  • Activated myosin heads now bind to actin and pulls the thin filament towards the centre of the sarcomere -POWER STROKE of the cross bridge cycle
  • Simultaneously – ADP and inorganic phosphate are released from the myosin head
  • As a new ATP molecule binds to the myosin head at the ATPase activity site, the myosin cross-bridge detaches from the actin
  • Sliding filament theory continues as long as there is calcium available
  • Removal of the calcium causes tropomyosin to move and inhibit binding
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4
Q

Muscle Contraction - relaxed muscle

A
  • Excitation is inhibited by the arrival of a nerve impulse at the muscle membrane
  • Without calcium the myosin binding site on actin is blocked by tropomyosin
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5
Q

The sliding Filament Theory

A
  1. Myosin head split ATP and become reoriented and energized
  2. Myosin heads bind to actin forming crossbridges
  3. Myosin heads rotate toward center of the sarcomere (power stoke)
  4. As myosin heads bind ATP, the crossbridges detach from actin

Contraction cycle continues if ATP is available and Ca2+ level in the sarcoplasm is high

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6
Q

Energy

  • Exergonic
  • Endergonic
  • Gibbs free energy
A

Exergonic - Process that releases (frees up) energy into its surroundings. Releases energy that can be used to perform work
Endergonic - Stores or absorb energy

Gibbs Free Energy

* Tells us which way a reaction will go 
* Spontaneity of a reaction - Free energy of products MINUS Free energy of reactants

∆G < 0

  • Reaction will occur by itself (spontaneous)
  • Favored
  • Exergonic

∆G > 0

  • Reaction cannot occur by itself (Not spontaneous)
  • Not favored
  • Endogenic

∆G = 0

  • No free energy change
  • Reaction is in equilibrium
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7
Q

Rate of bioenergetic

  • Enzymes
  • Enzymes & co-enzymes function as
  • Factors influencing enzyme function
A

Enzymes

  • Protein that catalyzes a biological reaction
  • Makes sure the outcome is always the same
  • Enzymes work together to form longer pathways such as the citric acid cycle – which is a series of chemical reactions that help us get out energy from CHO

Enzymes & co-enzymes function as

  • Biological catalysts
  • Couplers
  • Regulators of metabolism

Factors influencing enzyme function

  • pH
  • Temperature
  • Availability of substrate and enzyme
    • Enzyme-substrate complex
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8
Q

Adenosine Triphosphate (ATP)

A
  • Energy currency of cell
  • When the high energy bonds break, energy is produced
  • yields:
    31 KJ 7.3kcal.mol
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9
Q

Re-synthesis of ATP for muscle force generation

  • ATP in skeletal muscle
  • Anaerobic
  • Aerobic
A

ATP in skeletal muscle

  • 4-5 mmol/kg wet weight of muscle
    • Enough energy to sustain a few seconds of intense exercise (5-10)
  • Re-synthesis occurs at a rate sufficient enough to prevent a fall in the level of intramuscular ATP concentration

Anaerobic

  • Occurs in the sarcoplasm without O2
  • PCr hydrolysis
  • Anaerobic Glycolysis

Aerobic

  • Occurs in the mitochondria with O2
  • Aerobic glycolysis
  • Krebs cycle
  • Electron transport chain
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10
Q

Phosphocreatine (PCr) or Phosphogen System (ATP-PC)

  • PCr in skeletal muscle
  • Disadvantages
A

PCr in skeletal muscle

  • 3-4 x greater then ATP
  • Rapid supply without the use of O2
  • Large amount of free energy is released
  • As ATP availability decreases PCr is broken down, releasing energy for restoration of ATP
  • 43kJ per mole PCr
  • PCr in the muscle is immediately available at the onset of exercise and can be used resynthesize ATP quickly

Disadvantages

  • Limit capacity
  • Total amount of energy available is small
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11
Q

ATP and PCr

  • Adenylate kinase
  • Formation of AMP
A

ATP + ADP < - >ATP + AMP (AK as catalyst)

  • Kinase reaction that utilizes of two molecules of ADP to generate one molecule of ATP (one molecule of AMP)
  • This reaction in catalyzed by the enzyme adenylate kinase
  • Important during high intensity activity
  • Limited energy

Formation of AMP

  • A potent activator of a number of enzymes involved in energy metabolism
  • AMP acts as a important regulator
    • Phosphorylase (Glycogenolysis)
    • Phosphofructokinase (PFK)
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12
Q

Phosphogen system by-products and what they stimulate

A

By-products

  • Pi
  • AMP
  • ADP

By-products stimulate

  • Glycogenolysis
  • Glycolysis
  • Respiration pathways of mitochondria
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13
Q

Energy for activity lasting more then a few seconds

  • Glycogen
  • Glycolysis
  • Fate of pyruvate
A
  • Glycolysis anaerobic metabolism

Glycogen

  • Liver
    • Reservoir for blood glucose and brain
  • Muscle
    • Does not release into blood - only used for muscle metabolism
    • Muscle glycogen is biochemically efficient

Glycolysis

  • 4 ATP produced
  • 2 ATP molecules are used in the glycolysis process
  • NET of 2 ATP

Fate of pyruvate
- Lactate
- Aerobic metabolism
(depend on exercise intensity and metabolism capacity of the tissue)

Lactate

  • Can accumulate
  • Associated hydrogen ions can cause pH to drop
  • Lactate can be used to produced glycogen
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14
Q

Aerobic metabolism

  • Process
  • Amount of ATP produced
A

Pyruvate -> Acetyl-CoA -> TCA cycle -> electron transport chain (NADH & FADH to produce ATP)

Amount of ATP produced

  • 36-38 ATP from cellular respiration
  • Glycolysis produced 2 pyruvate - so everything is going to be multiplied
  • only 30-32 ATP actually enter the cells cytoplasm
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15
Q

Forms of Energy

  • Physiology
  • Heat as a by-product
A
  • Light
  • Chemical
  • Mechanical

Physiology

  • Mechanical energy - the capacity to do work
  • Work = force x distance
  • Power = work / time

Heat
- Heat is a by-product of mechanical energy, therefor change in heat or heat transfer can be used to measure energy content

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16
Q

Energy expenditure

- Expressed

A
  • Energy expended expressed in calories or joules
  • 1 calorie expresses the quantity of energy needed to raise 1ml of water by 1 degree Celsius
  • 1 joule expresses the quantity of energy needed to move 1g at a velocity if 1m/s
17
Q

Energy content in food

- Bomb Calorimeter

A

Direct calorimetry

  • Measures the energy content of food
    • CHO - 4.2 kcals (17.6kJ)
    • Fat - 9.4 kcal (40.2kJ)
    • Protein - 5.7 kcals (23.7kJ)

Rounded to correct for digestion and absorption in the human body

  • CHO - 4 kcal
  • fat - 9 kcal
  • Protein - 4 kcal
18
Q

Measuring Energy Expenditure

- Direct

A

Direct (measures energy expenditure from heat loss during a given activity)

  • Direct calorimetry chamber
    • A subject is placed in a sealed chamber with a supply of oxygen. Because the chamber is well insulated, the heat produced by the body is absorbed by a known volume of water that circulates through pipes located in the chamber
    • Very expensive
    • Required specially trained personnel
  • Direct calorimetry suit
19
Q

Measuring Energy Expenditure -> Indirect

  • Closed circuit spirometry
  • Open circuit spirometry
  • Respiratory chamber
  • Douglas bag
  • Breath by breath system
A
  • Refers to the measure of O2 uptake and CO2 production
  • Rate of O2 consumed directly related to the rate of energy produced

Closed circuit spirometry

  • Resting energy expenditure
    • Breath through mouth piece into spirometer filled with 100% O2
    • Expired gas passes back through spirometer and CO2 is trapped
    • O2 is consumed ↓ O2 in spirometer
    • Change in volume is measured and O2 uptake is used to calculate EE

Open circuit spirometry

  • Inhales ambient air
  • EE is measured from O2 and CO2 content of inspired and expired air
    • Douglas bag
    • Respiratory chamber
    • Breath-by-breath

Respiratory chamber

  • Gas exchange not heat
  • Ventilation rate monitored CO2 and O2 concentration monitored
  • Energy balance - food
  • Extremely expensive

Douglas bag

  • Inspire room air - expires through a mouth piece connected to a high flow, low resistance valve into a large plastic bag
  • Measures
    • Duration of collection
    • Volume of air collected

Breath by breath system
- Measures:
*Volume at the mouth piece
* Small gas sample is collected at every expiration
* Analysis of O2 and CO2 concentration
- Advantage of these systems:
* Analyse every breath
* Instant feedback
* Accurate estimate of energy expenditure
Portable versions have also be developed

20
Q

Components of energy expenditure

  • RMR
  • DIT
  • Exercise related energy expenditure
A

Resting metabolic rate (RMR) (40-75 %)

  • Energy required for normal body functions and homeostasis under resting conditions
  • Factors affecting RMR
    • Sympathetic nervous system
    • Thyroid hormone activity
    • Sodium potassium pump activity
  • Different body tissue have different energy requirements
    • Skeletal muscle (20% RMR)
    • Adipose tissue (5% RMR)

Diet-induced thermogenesis (DIT) (10%)

  • Thermic effect of food and is the increase in energy expenditure above resting metabolic rate that occurs for several hrs after eating
  • Sympathetic nervous system plays an important role in DIT
  • Storing fat in adipose tissue (3%)
  • CHO as glycogen (7% is lost)
  • Synthesis and breakdown of protein (24% of the available energy)

Exercise related energy expenditure

  • Thermic effect of exercise. All energy expended above the RER (respiratory exchange ratio) and DIT
  • 30% daily up to 80% in extreme
  • Voluntary - exercise
  • Involuntary - shivering, fidgeting or postural control

Exercise Nutrition (9 decks)

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