Module 7

• Energy


  Power derived from food to perform cellular work (physical activities, physiological activities, general maintenance and repair, food processing)
• Basal Metabolic Rate (BMR)


  Minimum kcal required for basic functions at rest
• Resting Metabolic Rate (RMR)

  Measured kcal required for basic functions at rest, typically 10-20% higher than BMR
• Factors affecting RMR


  • Body composition (more lean)
  • Increasing age (older adults)
  • Growth (kids, pregnancy)
  • Environmental temp
  • Body temperature (fever)
  • Fasting/starvation
  • Sex (females)
  • PA (during & 24h after)
• Physical Activity (PA)


  Metabolic cost of external work (job-related, transportation, domestic, exercise)
• Thermic Effect of Food (TEF)


  Energy required to process food (digest, absorb, transport, metabolize, store), estimated at 10% of Total Energy Expenditure (TEE)

  
• Components of Total Energy Expenditure (TEE)

  • Resting Metabolic Rate (RMR)
  • Physical Activity (PA)
  • Thermic Effect of Food (TEF)

  
• Metabolism


  Chemical (metabolic) processes by which the human body converts food and drink into energy
• Anabolism


  Building larger molecules from smaller ones, fueled by energy from catabolic reactions
• Catabolism


  Breaking down larger molecules into smaller ones, resulting in release of energy
• Under normal circumstances human cells rely on glucose, fat, protein metabolism
• Cells in the central nervous system are more dependent on glucose
• Metabolic Pathway


  Biochemical reactions that bring raw material to final product
• Adenosine Triphosphate (ATP)


  High-energy phosphate molecule, energy from catabolism of food used to build ATP, then broken down and energy released to power cellular work

  
• Mitochondria


  Organelles that synthesize most of the ATP that cells need to function, catabolize macronutrients and transfer energy released to ATP

  
• Adequate oxygen = aerobic metabolism, Inadequate oxygen = anaerobic metabolism
• Oxidation of Glucose to Produce ATP

  1. Glycolysis

  2. Acetyl CoA formation

  3. Citric Acid Cycle

  4. Electron Transport Chain
• Coenzyme


  Unlocks action of enzymes, analogy: car keys to car (enzyme)
• Citric Acid Cycle


  1. Acetyl CoA enters CAC & binds to oxaloacetate

  2. Citrate converted to intermediate compound (alpha-ketoglutarate), loses C in form of CO2

  3. Alpha-ketoglutarate loses CO2 and succinyl-CoA formed

  4. One ATP forms from GTP; succinate and fumarate release H+ ions picked up by FAD and NAD+

  5. End point -- 4C oxaloacetate is formed; available to bind with the next acetyl CoA so the cycle can repeat
• NAD+ and FAD


  Coenzymes that shuttle electrons and hydrogen ions
• Electron Transport Chain


  1. Coenzymes NADH and FADH2 carry H+ and high energy electrons from Citric Acid Cycle to ETC

  2. Electrons pass through chain with iron-containing cytochromes

  3. Cytochrome c facilitates bonding of 2 H+ with O, forming H2O

  4. Energy released during electron transfer; used to attach P to ADP, forming ATP
• Other Sources of Glucose

  • Other monosaccharides (fructose & galactose)
  • Glycogenolysis (glycogen --> glucose)
  • Gluconeogenesis (non-CHO precursor --> glucose)
• Fructose


  Broken down into glyceraldehyde --> converted to glycerol (backbone of triglycerides), only liver can use fructose for energy
• Galactose


  Converted in a two-step process into glucose (mainly in liver), catabolized via glycolytic pathway
• Glycogenolysis


  Breakdown of glycogen into glucose, coenzyme pyridoxal phosphate (PLP) needed
• Gluconeogenesis


  Synthesis of glucose from non-CHO precursors: glycerol, lactate, pyruvate and many amino acids, not the reverse of glycolysis
• Triglycerides


  Most energy-dense macronutrient group, body can extract energy from dietary fat or fat stored in fat tissue, adipocytes use hormone sensitive lipase (HSL) to facilitate lipolysis (removing three fatty acids from glycerol backbone)
• Glycogenolysis


  1. Breakdown of glycogen into glucose

  2. Coenzyme pyridoxal phosphate (PLP) needed
• Gluconeogenesis


  1. Synthesis of glucose from non-CHO precursors: glycerol, lactate, pyruvate and many amino acids

  2. Not the reverse of glycolysis; some steps in glycolytic pathway flow in only one direction (towards CAC)
• Triglycerides


  • Most energy-dense macronutrient group (more energy stored in triglycerides vs. glycogen)
  • Body can extract energy from dietary fat or fat stored in fat tissue
  • Adipocytes use hormone sensitive lipase (HSL) to facilitate lipolysis (removing three fatty acids from glycerol backbone)
• Glycerol removal from blood

  1. Liver converts glycerol to pyruvate or glucose (gluconeogenesis)

  2. Fatty acids used for energy
• Fatty acid preparation for catabolism

  1. Binding to coA (requires 2 ATP) in cytoplasm

  2. Pass through outer and inner mitochondrial membranes with help of carnitine

  3. Beta-oxidation in mitochondria
• Beta-Oxidation


  1. Fatty acids transported inside mitochondria

  2. Beta-oxidation breaks 16C palmitic acid into 2C units (forms 8 molecules of acetyl CoA, 7 NADH, 7 FADH2 (~28 ATP))
• Insufficient oxaloacetate


  Forms ketone bodies (ketogenesis)
• Glycerol (3C chain) can be used to produce ATP or small amounts of glucose
• If O2 & CHO are available

  Acetyl CoA enters CAC
• Lot's of ATP!! & H2O produced (106 ATP from 16C palmitic acid compared to 30-32 ATP from 6C glucose)

  
• Oxaloacetate


  Molecule derived from CHO
• Ketone bodies


  • Acetoacetate
  • Beta hydroxybutyric
  • Acetone
• Ketones can be used as energy (heart, muscle, kidney) and can even cross the blood-brain barrier and be used by the brain for half its energy needs (the other half still needs glucose – and it PREFERS GLUCOSE!)