Chapter 27 (continued) Specific Catabolic Pathways: Carbohydrate, Lipid & Protein Metabolism

Fatty Acids and Energy Fatty acids in triglycerides are the principal storage form of energy for most organisms. The energy yield per gram of fatty acid oxidized is greater than that per gram of carbohydrate oxidized.

five enzyme-catalyzed reactions cleaves carbon atoms two at a time from the carboxyl end of a fatty acid.  -Oxidation

Reaction 1:Reaction 1: the fatty acid is activated by conversion to an acyl CoA; activation is equivalent to the hydrolysis of two high-energy phosphate anhydrides.

 -Oxidation Reaction 2:Reaction 2: oxidation of the ,  carbon-carbon single bond to a carbon-carbon double bond.

 -Oxidation Reaction 3:Reaction 3: hydration of the C=C double bond to give a 2° alcohol. Reaction 4:Reaction 4: oxidation of the  alcohol to a ketone.

 -Oxidation Reaction 5:Reaction 5: cleavage of the carbon chain by a molecule of CoA-SH.

 -Oxidation This cycle of reactions is then repeated on the shortened fatty acyl chain and continues until the entire fatty acid chain is degraded to acetyl CoA.  -Oxidation of unsaturated fatty acids proceeds in the same way, with an extra step that isomerizes the cis double bond to a trans double bond.

Energy Yield from  -Oxidation Yield of ATP per mole of stearic acid (C 18 ). Glycolysis TOTAL 36

IF lauric acid (1) is metabolized through  -Oxidation, what are the products of the reaction after 3 turns of the spiral? Challenge Question (1)

Which C-18 fatty acid yields the greater amount of Energy: Saturated stearic acid? Monounsaturated oleic acid? Confirming your knowledge

Formation of Ketone bodies from lack of glucose A little Glucose needed to fully run  -Oxidation β-Oxidation Formation of Ketone Bodies for Energy (Low glucose levels) headaches.. ?

Ketone Bodies, see p e.g. e.g. acetone, B-hydroxybutyrate, and acetoacetate; are formed principally in liver mitochondria. can be used as a fuel in most tissues and organs. occurs when acetyl CoA builds up (due to limited glucose levels) vs the amt. of oxaloacetate available to react with it + take it into the Citric Acid Cycle

for example when: intake is high in lipids and low in carbohydrates. diabetes is not suitably controlled. Starvation occurs. Ketone Bodies are formed

Challenge Question What happens to the oxaloacetate produced from carboxylation of phosphoenolpyruvate? (i.e. where does it go and or where is it needed?) ?

Protein Catabolism Figure 27.7 Overview of Protein catabolism.

Nitrogen of Amino Acids Transamination A. -NH 2 groups move freely by Transamination Amino acids transfer amino groups to  -ketoglutarate  Glutamate...

Nitrogen of Amino Acids B. Oxidative Deamination nitrogens to be excreted are collected in glutamate, which is oxidized to  -ketoglutarate and NH 4 +. NH 4 + then enters the urea cycle.

The Urea Cycle – Overview a cyclic pathway that produces urea from CO 2 and NH 4 +. For step details see p

The Urea Cycle p

(Urine) The Urea Cycle (cont.)

Challenge Question NH3 and NH4 are both H2O soluble and could easily be excreted in urine. Why does the body convert them to Urea rather then excreting them directly?

Challenge Question 2 What are the molecular sources of Nitrogen in Urea? Hint: see Urea Cycle Reactions Steps 1-2 and 3 p

Heme Catabolism When red blood cells are destroyed: globin is hydrolyzed to amino acids to be reused. iron is preserved in ferritin, an iron-carrying protein, and reused. heme is converted to bilirubin in spleen  removed from blood (liver) then transferred to gallbladder (stored in the bile) finally excreted in the feces. When balance upset  [high bilirubin] in blood  jaundice: (yellowing of face and eyes) indicates Liver, spleen or gallbladder complications...

Final Challenge Question Why is High bilirubin content in the blood an indication of liver disease?