BIOENERGETICS AND METABOLISM
Review of Essential Terms
Energy: ability to do work
oWork: ability to produce force or generate heat
Bioenergetics: study of energy transformations in living organisms
Catabolism: break down
Anabolism: build up
Exergonic reactions: release of energy
Endergonic reactions: store or absorb energy
ATP, ADP, AMP: break bonds between phosphates to yield energy processes
Energy production
1st law of thermodynamics
oEnergy cannot be created or destroyed as it transforms form one form to another
without being depleted
Metabolic rate = the rate at which the body uses energy
oBody doesn’t produce, consume or use up energy (transforms from one to
another)
Metabolism: sum of all chemical processes necessary to maintain the body
Energy is required to…
Fuel vital body functions
Build and breakdown tissue
Contract muscle
Conduct nerve impulses
Regulate body temperature
oEnergy stored in the chemical bonds of adenosine triphosphate (ATP) is used to
power muscular activity. The replenishment of ATP in human skeletal muscle is
accomplished by 3 basic energy systems
Phosphagen, glycolytic, and oxidative
Main fuel source
Adenosine triphosphate (ATP)
oMost basic form of energy in the body
oBreakdown last “P” to “release” energy
Only readily usable form of energy
Macronutrients convert to ATP
oCarbs and protein yield 4.1 kcals per gram when burned
oFats yield 9.4 kcals/gram
oProtein mainly structural
Untrained individual demand carbs first, then fat, then protein
Trained individual demands fat first, then carbs, then protein
Fuel storage and energy
Carbohydrates
oLiver glycogen
oMuscle glycogen
oGlucose in body fluids
Fat
oSubcutaneous and visceral fat
oIntramuscular
Fuel conversion processes
Glycolysis = breakdown of glucose to ATP
Gluconeogenesis = protein or fat is converted to glucose
Glycogenesis = converting glucose into glycogen
Glycogenolysis = glycogen to glucose
RER or RQ
oRespiratory exchange ratio
Rate VCO2 over VO2
The body’s energy systems
ATP-PCr system
oAka immediate energy system/phosphagen system
oATP and CP are source of fuel
oStored ATP lasts about 2-3 seconds
oPCr is phosphocreatine (lasts about 15-20 seconds
PCr stored in the muscle
Used to rebuild ATP in the body
Rapid energy and rapid ATP regeneration
oSummary: lasts from 0 to 30 seconds max
Anaerobic (Glycolysis)
oAka glycolytic system
oUsed at start of exercise or for high intensity exercise
o15-30 seconds up to 2-3 minutes
oCreates and provides ATP by breaking down (partial degradation) glucose or
glycogen
oO2 not required
oGenerates lactic acid via short term activity
oAverage person stores 2000-25000 kcals of glycogen (stored muscle and liver
glycogen
Aerobic (Oxidative Phosphorylation)
oAka oxidative system
oOccurs in mitochondria of cytoplasm
oProvides ATP at rest and low to moderate intensity exercise lasting longer than 2-
3 minutes
oRequires O2 to generate an abundance of ATP
oConsists of the following energy processes/cycles
Glycolysis (takes place in cytoplasm) – stage 1
For many tissues, the process of glycolysis provides “emergency
energy”
Sets the stage for “aerobic oxidation”
Glucose 2 pyruvate molecules (pyruvic acid)
4 ATP produced and 2 ATP consumed = 2 ATP
oIf glycogen is used, then net ATP will be 3 ATP due to by
stepping the glucose to glucose 6 phosphate stage”
Fast vs. slow glycolysis
oDuring fast glycolysis, pyruvate is converted to lactic acid
Provides ATP at a fats rate
Will not proceed to Kreb’s
High intensity, short duration exercise
oDuring slow glycolysis, pyruvate is transported to the
mitochondria for use in the oxidative system
Kreb’s cycle (takes place in mitochondria) – stage 2
Production of pyruvic acid, from glycolysis helps in the beginning
of the Kreb’s cycle
Aka citric acid cycle
oAfter 2 rotations, Acetyl CoA Is oxidized to 2 ATP
Doesn’t require oxygen and leads to metabolism of fats
Main roles are to spin off and produce FADH2 and NADH to be
used in ETC
oApproximately 20 hydrogen ions sent to ETC
Electron transport chain (takes place in mitochondria) – stage 3
Provides a great amount of energy, but requires the use of oxygen
(much longer process)
Hydrogen, released from glycolysis and Krebs, plays a major role
in ETC. combines FADH2 and NADH, carried to ETC and splits
apart into protons and electrons
Hydrogen will combine with oxygen to produce ATP and water (at
the end of ETC)
Electrons pass through a series of reactions and ultimately produce
energy for phosphorylation of ADP into ATP
Hence, glucose molecule will yield 32-33 ATP and the end
o2-3 ATP from glycolysis
o2 ATP from Krebs
o28 ATP from ETC
Oxidation of fat
Stored fat can provide 60,000 to 100,000 kcals
Triglycerides are stored in fat calls and between and within muscle fibers
oTriglycerides must be broken down to glycerol and 3 molecules of “free fatty
acids”
The process is lipolysis
FFA are the primary energy source
FFA can enter blood and be transported throughout the body, once it is
freed from glycerol
Increased FFA concentration forces FFA into muscle
Beta oxidation (breaking down fat into 2 small carbon chaisn) of FFA within
mitochondria, converts FFA to 8 acetic acids, which are then converted into Acetyl CoA
Acetyl CoA then enters into the Krebs
By products of beta are similar to breakdown of glucose, yet more carbon results, which
gives more acetyl CoA and causes more electrons to enter ETC
Protein metabolism
Through gluconeogenesis, some amino acids can be converted into glucose
Also, some amino acids can be converted into pyruvate and acetyl CoA
When amino acids are catabolized, some nitrogen is used to make new AA while some is
converted into urea, and then excreted
Lactic acid, energy use and metabolism
Use and production of lactate
As glycolysis speeds up, hydrogen production speeds up and accumulates
oWhen hydrogens accumulate, pyruvate can pick up a hydrogen and form lactate
oLactate will be used as a source of fuel, out of necessity, when enough hydrogen
carriers are not available
If intensity of exercise is high enough, lactate results, but when intensity becomes less,
lactate is transformed back to pyruvate
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