Chemistry 451

Lecture #26: Lipid Metabolism: Digestion, Fatty Acid Oxidation and Ketone Bodies Read: pg. 563-564; 568-575; 580-581 (Ketone Bodies)

HW (Due Monday, Nov 20): pg. 609 (study exercises 1, 2, 3, 5 AND problem 2)

Optional Reading: pg. 566-567; Optional HW: pg. 609 (problems 3, 4)

Optional HW Make-up (a compromise between required HW and Extra Credit): Complete Student Satisfaction Inventory: Due Friday, in class or chem office by 11:00am. Pick up inventories in chem office if you did not get one in class.

For your Listening Pleasure: Beta-Oxidation (a great tune; Highly Recommended)!

Hang up posters BEFORE class on Friday

Review at least 1 poster during last 20 min of class on Friday

 

Objectives:

  1. Know that triacylglycerol mobilization depends on the emulsifying activity of bile acids and the activation of lipases (e.g. pancreatic lipase) at the lipid-water interface. After they are absorbed, the lipid digestion products are packaged in lipoproteins for transport to the tissues via the blood. Know the role of lipoprotein lipase in liberating fatty acids and monoacylglycerides for uptake into muscle and adipose cells.
  2. Fatty acids are released from triacylglycerols in their storage sites in adipose tissue by hormone-sensitive lipase and carried in the blood as albumin complexes to their sites of oxidation. Know the role of hormone sensitive lipase in mobilizing fatty acids for transfer from adipocytes to other tissues.
  3. Fatty acid oxidation begins with the activation of the acyl group by formation of a thioester with CoA. The acyl group is transferred to carnitine for transport into the mitochondria, where is reesterified to CoA.
  4. Beta oxidation chops 2 carbons off a fatty acid each time it goes around making the process look like a spiral. Each 2 carbon unit and the final carbon unit is acetyl CoA. (Fatty acids with odd numbers of carbon atoms are chopped into acetyl-CoA and one molecule of propionyl CoA). The acetyl-CoA is oxidized by the citric acid cycle and oxidative phosphorylation to generate ATP.
  5. Beta oxidation occurs in four reactions (note which are similar to three reactions starting with succinate in the Citric Acid Cycle):
  1. The liver uses acetyl Co-A to synthesize ketone bodies (acetoacetate and beta hydroxybutyrate). Tissues that use these ketone bodies for fuel convert them back to acetyl-CoA. (The brain can not use fatty acids as a fuel because the fatty acids do not cross the blood brain barrier, but during starvation, the small water soluble ketone bodies become the brain's major fuel source). During starvation (when glucose is low) the 2 carbon units (acetyl CoA) are converted to ketone bodies (they can’t enter the Kreb’s cycle because they need to combine with oxaloacetic acid. Oxaloacetic acid is sucked off for the production of glucose for the brain when glucose is low).
  2. Acetone (a ketone body) can be tasted and smelled on the breath during starvation (low blood sugar) and diabetes and after drinking ethanol.
  3. Know why ketosis is associated with metabolic acidosis.

Check out Olean (Olestra) the fat free "food"