Nutrition and Metabolism

I. Nutrition

A. Overiew

• Classes of nutrients: Carbohydrates, Lipids, Proteins, Water, Vitamins, Minerals
• Essential versus non-essential nutrients
  
• 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
• Food Pyramid Diagram

B. Carbohydrates

• 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

C. Lipids

• 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

D. Proteins

• 20 amino acids
• Used in synthesis of enzymes, antibodies, hemoglobin, muscle, etc...
• Complete or incomplete depending if the source has all amino acids needed byb 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

E. Vitamins

• Two classes
  • Fat soluble - A, D, E, K
  • Water soluble - C and B (thiamine, riboflavin, nicotinamide, pyridoxine, biotin, cyanocobalamin, folic acid)
• Uses
  • Antioxidants (A,C&E),
  • Hormone synthesis (D)
  • Required for clotting proteins (K)
  • Coenzymes (B vitamins)
• RDA varies with each vitamin

F. Minerals

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

G. Water (discussed in fluid and electrolyte chapter)

II. Metabolism

A. Metabolism

• 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
• Metabolism overview  Diagram Diagram

B. Carbohydrate Metabolism Diagram

i. 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 Diagram

• 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

iv. Krebs Cycle Diagram

• 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

v. Electron Transport Chain Diagram

• 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

vi. Chemiosmosis Diagram

• Hydrogen ion concentration gradient used to synthesis many ATP molecules
• ATPsynthase in the membrane uses the kinetic energy of hydrogen ion diffusion to bond phosphate to ADP, thereby creating ATP molecules

viii. Glucogenesis and Glycogenolysis

• Glycogenolysis - glycogen stored in liver and muscles is lyzed into individual glucose molecules
• Gluconeogenesis - glycerol and amino acids are used to synthesize glucose

C. Lipid and Protein Metabolism

i. Lipid Metabolism Diagram

• Lipogenesis - triglyceride synthesis (when cellular ATP and glucose levels are high)
• Lipolysis - lysis of trigylcerides into glycerol and fatty acids (when cellular ATP and glucose levels are low) and these products are used to synthesize molecules used in glycolysis and Kreb cycle (e.g., use of fattyc acids to produce Acetyl CoA and ketone bodies)

ii. Protein metabolism Diagram

• Tissue protein structure doesn't last long
• Amino acids consumed are used to replace lysed denatured proteins
• If amino acids are in excess the are converted into molecules used in glycolysis and Krebs cycle

D. Overview of Process

• Diagram