BIOCHEM

• Triglycerides (fats and oils)


  are important dietary sources of energy.  Fat also functions as a major form of energy storage (9 cal/g).
• Lipids


  Because it is water-insoluble, fat can be stored in larger quantities than carbohydrates.
• Lipids

  Carbohydrate reserves are depleted after about 1 day without food,  but stored fat can provide needed calories for 30-40 days.
• Digestion of Triglycerides


  During digestion, triglycerides are hydrolyzed to glycerol, fatty acids,  and monoglycerides:
• Phosphoglycerides


  are also hydrolyzed to their component  substances (glycerol, fatty acids, phosphate groups, and  aminoalcohols).
• Chylomicrons


  The smaller molecules that are produced, along  with cholesterol.
• Chylomicrons

  • modified by the liver into  smaller lipoprotein particles.
  • phosphoglycerides, and cholesterol are complexed  with proteins to form lipoprotein aggregates
• • The concentration of plasma lipids increases after a meal, and returns  to normal as a result of storage in fat depots and oxidation to provide  energy.
  • The concentration of plasma lipids rises within 2 hours after a meals,  peaks after 4-6 hours, then drops to normal levels.
• Lipoproteins may be classified by density.
• Chylomicrons carry triglycerides from the intestines to the liver,  skeletal muscle, and adipose tissue.
• Very-low-density lipoproteins (VLDL)


  carry newly synthesized  triglycerides from the liver to adipose tissue.
• Low-density lipoproteins (LDL)


  carry cholesterol from the liver to cells  of the body or bad cholesterol
• High-density lipoproteins (HDL)


  collect cholesterol from the body’s  tissues, and bring it back to the liver or good cholesterol.
• Cholesterol


  is involved in the formation of cell membranes, the insulation of  nerves, the synthesis of a number of hormones, and the digestion of food.
• Resin drugs (Questran, Colestid)


  bind with bile acids in the digestive tract and  remove them from operation
• Lopid, or large doses of niacin


  reduce the production of triglycerides, whichare involved in the formation of LDL
• Statins (Mevacor, Zocor, Pravachol, Lipitor)


  block the synthesis of cholesterol  in the liver by inhibiting HMG-CoA reductase
• Brain cells do not obtain nutrients from blood.
• Red blood cells do not have mitochondria, and cannot do fatty acid  oxidation.
• Glycogen and Glucose Stores


  Carbohydrates from dietary sources and glycogen catabolism are used  preferentially for energy production
• Fat mobilization


  When cells need fatty acids for energy, the endocrine system  produces several hormones, including epinephrine which enter the bloodstream.
• In the blood, mobilized fatty acids form a lipoprotein with the plasma protein  called serum albumin.
• Fat Mobalization


  In this form, the fatty acids are transported to the tissue cells that need them.
• The glycerol is water soluble, so it dissolves in the blood and is also  transported to cells that need it.
• Glycerol Metabolism


  The glycerol hydrolyzed from triglycerides can provide energy to cells.  It is converted to dihydroxyacetone phosphate in two steps:
• Dihydroxyacetone phosphate is one of the chemical intermediates in  glycolysis. It is converted to pyruvate, and thus contributes to cellular  energy production.

  The pyruvate can also be converted to glucose through gluconeogenesis.
• Fatty Acid Oxidation


  Fatty acids that enter tissue cells cannot be oxidized to produce energy until they pass through the membrane of the mitochondria.  
• 1. Fatty Acid Oxidation
  2. This reaction is catalyzed by acyl CoA synthetase.
  3. This reaction is referred to as activation of the fatty acid because the  fatty acyl CoA is a high energy compound
• β-oxidation


  The fatty acyl CoA molecules that enter the mitochondria then undergo a catabolic process
• Plasma


  Liquid portion of the blood
• Blood Sugar


  glucose part in the blood
• RCBS - Erythrocytes


  no nucleus and mitochondria
• RCBS


  cannot do fatty acid oxidation (atp production)
• Four reaction

  1. Dehydrogenation
  2. Hydration
  3. Dehydrogenation
  4. Release of the acetyl unit
• β-oxidation of Fatty acids

  In the final step of b-oxidation (Step 4), the bond between the a- and b-  carbons is broken by reaction with coenzyme A.
• β-oxidation of Fatty acids

  A new fatty acyl CoA is  formed, which is two carbons shorter than the original molecule, and a  unit of acetyl CoA is released
• Thus, the breakdown of 18-C stearic acid requires 8 passes through  the spiral, and produces 9 acetyl CoA’s, but only 8 FADH2 ’s and 8  NADH’s.
• The activation of stearic acid by coenzyme A to form stearoyl CoA comes from the hydrolysis of 2 ATP’s
• As a stearoyl CoA molecule (18 C’s) passes through the b-oxidation spiral, 9 acetyl CoA’s, 8 FADH2 ’s, and 8 NADH’s are produced.
• Acetyl CoA can enter the citric acid cycle / electron transport chain and form 10 ATP’s = 90 ATP’s