Energy Expenditure Flashcards
Sarcomeres
- What are sarcomeres
- Striations
- Z discs
- M line
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
Myosin & Actin
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
Muscle Contraction
- 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
Muscle Contraction - relaxed muscle
- 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
The sliding Filament Theory
- Myosin head split ATP and become reoriented and energized
- Myosin heads bind to actin forming crossbridges
- Myosin heads rotate toward center of the sarcomere (power stoke)
- 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
Energy
- Exergonic
- Endergonic
- Gibbs free energy
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
Rate of bioenergetic
- Enzymes
- Enzymes & co-enzymes function as
- Factors influencing enzyme function
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
Adenosine Triphosphate (ATP)
- Energy currency of cell
- When the high energy bonds break, energy is produced
- yields:
31 KJ 7.3kcal.mol
Re-synthesis of ATP for muscle force generation
- ATP in skeletal muscle
- Anaerobic
- Aerobic
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
Phosphocreatine (PCr) or Phosphogen System (ATP-PC)
- PCr in skeletal muscle
- Disadvantages
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
ATP and PCr
- Adenylate kinase
- Formation of AMP
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)
Phosphogen system by-products and what they stimulate
By-products
- Pi
- AMP
- ADP
By-products stimulate
- Glycogenolysis
- Glycolysis
- Respiration pathways of mitochondria
Energy for activity lasting more then a few seconds
- Glycogen
- Glycolysis
- Fate of pyruvate
- 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
Aerobic metabolism
- Process
- Amount of ATP produced
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
Forms of Energy
- Physiology
- Heat as a by-product
- 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
Energy expenditure
- Expressed
- 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
Energy content in food
- Bomb Calorimeter
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
Measuring Energy Expenditure
- Direct
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
Measuring Energy Expenditure -> Indirect
- Closed circuit spirometry
- Open circuit spirometry
- Respiratory chamber
- Douglas bag
- Breath by breath system
- 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
Components of energy expenditure
- RMR
- DIT
- Exercise related energy expenditure
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
