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Introduction to Metabolism. What is a Nutrient?. Nutrients =any substance in food that is used by the body to promote normal growth, maintenance, and repair. Essential nutrients must be consumed in the diet. There are six classes of nutrients. Overview

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what is a nutrient
What is a Nutrient?
  • Nutrients=any substance in food that is used by the body to promote normal growth, maintenance, and repair.
  • Essential nutrients must be consumed in the diet.
  • There are six classes of nutrients.


  • Classes of nutrients: Carbohydrates, Lipids, Proteins, Water, Vitamins, Minerals
  • RDA - recommended dietary amounts
  • Energy value of foods - kilocalorie - amount of heat energy to raise the temperature of 1 kilogram of water 1 degree Celsius
  • Composed of C, H, O
  • Provide a major source of fuel for the body
  • Basic unit is glucose
  • Simple versus Complex
  • Energy yielding (4 kcal /gm)


  • Divided into simple carbohydrates and complex carbohydrates
  • Used in the process of ATP synthesis
  • Simple carbohydrates examples: soft drinks, candy, fruit, ice cream, pudding
  • Complex carbohydrates: bread, cereal, crackers, flour, pasta, nuts, rice, potatoes
  • RDA - 125-175 grams = 55-60% of total caloric intake


  • Classes: triglycerides, phospholipids, sterols
  • Used in cell membrane synthesis, energy production, vitamin storage
  • Animal sources: lard, meat, poultry, eggs, milk, milk products
  • Plants sources: chocolate, corn soy, cottonseed, olive oils, coconut, peanuts
  • Cholesterol sources: organ meats and egg yolks
  • RDA - 80-100 grams = 30% or less of total caloric intake


  • 20 amino acids 9 essential and 11 non-essential
  • Used in synthesis of enzymes, antibodies, hemoglobin, muscle, etc...
  • Complete or incomplete depending if the source has all amino acids needed by the body
  • Complete protein sources: eggs, milk meat (fish, poultry, pork, beef, lamb)
  • Incomplete protein sources: legumes, nuts and seeds, grains and cereals
  • RDA - 0.8g/kg of body weight = 10-15% of total caloric intake


  • Two classes
    • Fat soluble - A, D, E, K
    • Water soluble - C (ascorbic acid) and B

B1: thiamine

B2: riboflavin

B3: nicotinamide (niacin)

B5: pantothenic acid

B6: pyridoxine


B12 cyanocobalamin

Folic acid



    • Antioxidants (A,C&E),
    • Hormone synthesis (D)
    • Required for clotting proteins (K)
    • Coenzymes (B vitamins)
  • RDA varies with each vitamin


  • Seven required (calcium, phosphorus, potassium, sulfur, sodium. chloride, and magnesium)
  • Trace minerals needed (fluorine, cobalt, chromium, copper, iodine, iron, manganese, selenium, zinc)
  • Uses in bone formation, nerve transmission, cofactors of enzymes, protein synthesis, etc....


  • sum of all the reactions occurring in the body at any given time; a balance between catabolic and anabolic reactions
  • Catabolism – breakdown of complex organic compounds into simpler ones; reactions and are considered exergonic (gives off energy) and produces more energy than they consume
  • Anabolism – combining small organic compounds into larger ones; reactions are endergonic (requires energy) and consume more energy than they produce
  • Chemical reactions of living systems depend on efficiently transforming energy from one molecule to another. ATP (adenosine triphosphate) accomplishes this task.
  • ATP  ADP + P + ENERGY

Composed of three pathways: Glycolysis, Krebs cycle, and Electron transport chain

  • ii. Glucose actively transported in GI tract then insulin-mediated facilitated diffusion in body cells
  • iii. Glycolysis
  • Occurs in the cytosol
  • One six carbon glucose is split into two three carbon pyruvate
  • 2 ATPs are used but 4 are created
  • 2 nicotinamide adenine dinucleotide (NAD) are hydrogenated

Krebs Cycle

  • Pyruvate from glycolysis is converted into Acetyl CoA in cytosol (NAD is hydrogenated and carbon dioxide is released)
  • Acetyl CoA is shuttled into the mitochondria
  • Series of reactions takes place
  • One ATP is created (per Acetyl CoA)
  • 2 carbon dioxides are released
  • 3 NADs are hydrogenated
  • One flavin adenine dinucleotide (FAD) is hydrogenated

Electron Transport Chain

  • Occurs in the inner mitochondrial membrane
  • Electrons and hydrogens are released from NADs and FADs
  • Oxygen is the final electron acceptor -- if no oxygen present lactic acid produced from pyruvate and krebs does not occur -- referred to as anaerobic carbohydrate metabolism
  • Hydrogen ions form a concentration gradient
summary of carbohydrate metabolism1
Summary of Carbohydrate Metabolism
  • A total of 36 ATP are produced from the complete breakdown of a glucose molecule.
  • Water and carbon dioxide are released as by products.
  • Chemical Equation for the entire reaction:

C6H12O6 + 6O2 6H20 + 6CO2 + 36 ATP + heat

lipid metabolism
Lipid Metabolism
  • Lipogenesis= triglyceride synthesis
  • Lipolysis=

“fat splitting”

metabolic rate and heat production
Metabolic Rate and Heat Production
  • Metabolic rate=the body’s rate of energy output
  • Basal metabolic rate=the minimum energy expended in a fasting state (12 hours) to keep a resting, awake body alive in a warm, quiet environment.