Bioenergetics

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Bioenergetics

• Nutrient Role
• in Bioenergetics

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Bioenergetics

• Bioenergetics refers to the flow of energy within
  a living system.
• Energy is the capacity to do work.

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Energy and Laws of Thermodynamics

• First law Energy is neither created nor
  destroyed, but instead, transforms from one state
  to another without being used up.
• There are six forms of interchangeable energy
  states.
• Chemical
• Light
• Electric
• Mechanical
• Heat
• Nuclear

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Bioenergetics

• The bodys capacity to extract energy from food
  and transfer it to the contractile elements in
  skeletal muscle determines capacity to exercise
  at high intensity.

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Bioenergetics

• Energy transfer occurs through chemical reactions
  utilizing a mixture of nutrients and the use of
  oxygen.
• Aerobic describes such oxygen-requiring energy
  reactions.
• Anaerobic chemical reactions generate energy
  rapidly for short durations without oxygen.

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Bioenergetics

• Anaerobic and aerobic breakdown of ingested
  nutrients provides the energy for synthesizing
  the chemical fuel that powers all forms of
  biologic work.

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Energy Extraction

• The energy from nutrients is harnessed to perform
  many complex biologic functions.
• Muscular activity
• Digestion, absorption, and assimilation of food
  nutrients
• Glandular function that secretes hormones
• Maintenance of electrochemical gradients across
  cell membranes
• Synthesis of new chemical compounds and tissues

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ATP The Energy Currency

• Potential energy from food is conserved within
  the bonds of ATP.
• In the degradation of one mole of ATP to
  adenosine diphosphate (ADP), the outermost
  phosphate bond splits and liberates approximately
  7.3 kCal of free energy.
• ATP is the compound that is directly used to fuel
  many chemical reactions.

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ATP The Energy Currency

• Food provides the major sources of potential
  energy to rejoin ADP and phosphate ion to form
  ATP.
• Some energy for ATP resynthesis, however, comes
  directly from the anaerobic splitting of a
  phosphate from phosphocreatine (PCr).

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Cellular OxidationReduction

• Dehydrogenase coenzymes catalyze hydrogens
  release from nutrient substrates.
• The coenzyme part of the dehydrogenase,
  nicotinamide adenine dinucleotide (NAD), or
  flavin adenine dinucleotide (FAD) accepts pairs
  of electrons from hydrogen.

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Oxidative Phosphorylation

• Three conditions must exist for the continual
  resynthesis of ATP from macronutrient catabolism.
• Availability of the reducing agents in the
  tissues
• Presence of an oxygen in the tissues
• Sufficient concentration of enzymes and
  mitochondria in the tissues

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Oxidative Phosphorylation

• A biochemical steady state exists when hydrogen
  atoms oxidize at their rate of formation.
• In strenuous exercise, inadequacy in oxygen
  delivery or its rate of use creates a relative
  imbalance between hydrogen release and its final
  acceptance by oxygen.

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Formation of Lactate

• During intense exercise, when hydrogen oxidation
  does not keep pace with its production, lactate
  forms as pyruvate and temporarily binds hydrogen.

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Lipid As a Fuel

• Stored fat represents the bodys most plentiful
  source of potential energy.
• The complete breakdown of a triacylglycerol
  molecule yields about 460 molecules of ATP.

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Lipid As a Fuel

• Numerous interconversions take place among the
  food nutrients.
• Fatty acids represent a noteworthy exception, as
  they cannot be synthesized to glucose.
• Fatty acid catabolism requires oxygen.

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Sources for Fat Catabolism

• Triacylglycerol stored within the muscle fiber
• Circulating triacylglycerol in lipoprotein
  complexes
• Hydrolyze catalyzed by lipoprotein lipase
• Circulating free fatty acids mobilized from
  adipose tissue

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Fatty Acids

• Beta (ß)-oxidation converts a free fatty acid to
  multiple acetyl-CoA molecules.
• Acetyl-CoA molecules are oxidized further in the
  citric acid cycle.
• The released hydrogens oxidize through the
  respiratory chain.
• Each 18-carbon fatty acid molecule generates 147
  molecules of ATP.

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Lipogenesis

• Lipogenesis is the formation of fat, mostly in
  the cytoplasm of liver cells.
• Excess glucose or protein converts into stored
  triacylglycerol.
• This process requires ATP energy and the B
  vitamins biotin, niacin, and pantothenic acid.

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Protein

• Protein serves as a potentially important energy
  substrate.
• Nitrogen is removed from the amino acid molecule
  via deamination.
• The remaining carbon skeletons enter metabolic
  pathways to produce ATP.

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Protein Breakdown

• Protein catabolism facilitates water loss.
• The amine group and other solutes from protein
  breakdown must be eliminated.
• This requires excretion of obligatory water as
  the waste products of protein catabolism leave
  the body dissolved in fluid (urine).
• For this reason, excessive protein catabolism
  increases the bodys water needs.

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