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Chapter 3
Bioenergetics
Objectives
Discuss the function of cell membrane,
nucleus, & mitochondria
Define: endergonic, exergonic, coupled
reactions & bioenergetics
Describe how enzymes work
Discuss nutrients used for energy
Identify high-energy phosphates
Objectives
Discuss anaerobic & aerobic production of
ATP
Describe how metabolic pathways are
regulated
Discuss the interaction of anaerobic &
aerobic ATP production during exercise
Identify the rate limiting enzymes
Introduction
Metabolism: total of all chemical reactions that
occur in the body
– Anabolic reactions - Synthesis of molecules
– Catabolic reactions - Breakdown of molecules
Bioenergetics
– Converting foodstuffs (fats, proteins, carbohydrates)
into energy
Substrate – Substance used by body in
metabolism
Metabolite – Byproduct of metabolism
Energy Forms
Energy originates in the sun
– Chemical
– Light
– Mechanical
– Electrical
– Heat
– Nuclear
Photosynthesis
Energy from the sun
– Solar energy from sun converted to chemical
energy in plants
– Plants use energy + water and carbon dioxide
– Byproduct is oxygen
– Build food molecules
Thermodynamics
1st Law
– Conservation of energy-energy cannot be
created or destroyed.
– They can be interchanged
– Our bodies transform energy into a form that
we can used.
Biological Energy Cycle
Food + O2 → CO2 + H2O + energy
Chemical
Mechanical
60-70% of this energy is heat
The rest is used for
– Muscle contraction
– Cellular operations (respiration)
Digestion and absorption
Synthesis of new compounds
Glandular function
Biological Energy Cycle
Chemical energy transformation to
mechanical energy
Food (Chemical energy) is used for
muscular contraction (Mechanical energy)
Elements
Basic chemical substances
–
–
–
–
Oxygen
Carbon
Hydrogen
Nitrogen
Minor elements
– Sodium, Iron, Zinc, Potassium, Magnesium, Chloride,
Calcium
Organic substances – contain carbon
Inorganic substances - do not contain carbon
Cell Structure
Cell membrane
– Protective barrier between interior of cell and
extracellular fluid
– Maintains ion concentrations (unequal)
Nucleus
– Contains genes that regulate protein
synthesis
Cell Structure
Cytoplasm
– Fluid portion of cell
– Contains organelles (mitochondria)
– Glycolysis – enzymes
– Mitochondria
Structure of a Typical Cell
Fig 3.1
Cellular Chemical Reactions
Endergonic reactions
– Require energy to be added
– Photosynthesis – solar energy to chemical
energy
Energy stored
Exergonic reactions
– Release energy
– Breakdown of cellular bonds
The Breakdown of Glucose:
An Exergonic Reaction
Fig 3.3
Coupled Reactions
Fig 3.4
Cellular Chemical Reactions
Coupled reactions
– Liberation of energy in an exergonic reaction
drives an endergonic reaction
– Breakdown of glucose-exergonic
– Formation of ATP-endergonic
Oxidation-Reduction Reactions
Oxidation: removing an electron
– Removing a negative charge = + >
– (oxygen not required)
Reduction: addition of an electron
– Adding a negative charge = - >
Oxidation and reduction are always
coupled reactions
Oxidation-Reduction Reactions
Reducing agent: molecule that donates an
electron
Oxidizing agent: molecule that accepts an
electron
Oxidation-Reduction Reactions
In cells often involve the transfer of
hydrogen atoms rather than free electrons
– Hydrogen atom contains one electron
– A molecule that loses a hydrogen also loses
an electron, and therefore is oxidized
Transfer of H+ and eMajor transport molecules in bioenergetics
– Nicotinamide adenine dinucleotide
– Niacin (B3)
– NAD – oxidized form
– NADH – reduced form
Transfer of H+ and eMajor transport molecules in bioenergetics
– Flavin adenine dinucleotide
– Riboflavin (B2)
– FAD – oxidized form
– FADH – reduced form
Enzymes
Catalysts that regulate the speed of
reactions
– Lower the energy of activation
Energy required to initiate the reaction
– Speed up the rate of the reaction
– Increase the rate of product formation
Enzymes Lower the
Energy of Activation
Fig 3.6
Enzymes
Factors that influence enzyme activity
– Temperature
Optimum temperature – most active
Slight increase increases activity of most enzymes
Useful for muscular contraction
– pH
Optimum pH
Altered pH reduces enzyme activity
High intensity exercise (LA) - ↓ pH
Decreases ability to produce energy (ATP)
Extreme acidity is a limiting factor in exercise.
Enzymes
Structural characteristics
– Large proteins with 3 D shape
– Characteristic grooves and ridges
Active sites
– Interact with specific substrates
Lock and key model
EnzymeSubstrate
Interaction
Complex lowers energy of
activation
Reaction proceeds
Fig 3.7
Fuels for Exercise
Carbohydrates
– Glucose – C6H12O6 (4 kcal/gram)
Monosaccharide
Stored as glycogen (C6H12O6)n
– Disaccharides
Sucrose
– Polysaccharides
Cellulose
Starch
Fuels for Exercise
Fats
– Carbon, hydrogen, oxygen
– Groups
Fatty acids – energy source (9 kcal/gram)
– Stored as triglycerides-fat cells, skeletal muscle
– Lipolysis-fatty acids and glycerol
Phospholipids – not an energy source
– Structural component-cell membranes, myelin sheath
Steroids – not an energy source
– Structural component-cell membranes
– Synthesis of hormones
Fuels for Exercise
Proteins
– Not a primary energy source during exercise
– Amino acids
– Limited usage
Extreme exercise conditions
Adenosine Triphosphate
We convert food:
– Fat, Carbohydrate (CHO), Protein (limited)
Into energy:
– Adenosine TriPhosphate (ATP)
Adenosine is a complex structure
Phosphates (3 simpler structures)
Adenosine
(P) ≈ (P) ≈ (P)
Structure of ATP
Fig 3.8
Model of ATP as the Universal
Energy Donor
Fig 3.9
ATP
Adenosine
(P) ≈ (P) ≈ (P)
ATP + H2O → ADP + Pi
ATPase
7,000 to 12,000 calories or
7 to 12 kilocalories
Breakdown requires regeneration
Coupled reaction
Coupled Reaction
ATP + H2O ←→ ADP + Pi
ATPase
ADP + C~P ←→ ATP + C
Creatine kinase
Bioenergetics
Cells need constant supply of ATP
Minimal amounts stored for cellular processes
Muscular contraction-exercise
– Constant, large supply
Formation of ATP (3 metabolic pathways)
– 1. Phosphocreatine (PC) breakdown
ATP-PC system (phosphagen system)
– 2. Degradation of glucose and glycogen
Glycolysis (Glycolytic system)
– 3. Oxidative phosphorylation
Tricarboxylic cycle, Krebs cycle
Bioenergetics
Anaerobic pathways (do not involve O2)
– 1. ATP-PC breakdown
– 2. Anaerobic glycolysis
Aerobic pathway
– Requires O2
– 3. Oxidative phosphorylation
1. ATP-PC (Phosphagens)
Characteristics
– ATP and PC stored in the contracting mechanism of
the muscle
– Simplest and fastest way to produce ATP
ATP + H2O → ADP + Pi
ATPase
– Provides energy for short term, maximal exercise
5 sec
– High intensity activity
30 sec
1. ATP-PC (Phosphagens)
Characteristics (cont)
– At onset of exercise-rapid breakdown followed
by rapid resynthesis
ADP + C~P ←→ ATP + C
Creatine kinase
– ATP replenishment by PC maintains ATP
levels for awhile.
– PC replenishment continues activity about 30
sec
1. ATP-PC (Phosphagens)
Characteristics (cont)
– 3 times more CP than ATP stored in muscle
– Fastest rate of energy production, lowest stores
(capacity)
– Used during
Initial onset of exercise (oxygen deficit)
Short term, high intensity exercise (< 5 sec)
– Resynthesis only during recovery
– Activities (examples)
Sprints (< 30 sec)
High jumping
Weight lifting
E nerg y T ran sfer S ystem s an d E xercise
10 0%
% Capacity of Energy System
A naero bic
G lycolysis
A erobic
E nergy
S ystem
ATP - CP
10 sec
30 se c
2 m in
5 m in +