Chapter 27 (continued)
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Transcript of Chapter 27 (continued)
![Page 1: Chapter 27 (continued)](https://reader035.fdocuments.in/reader035/viewer/2022081519/56813678550346895d9e06ed/html5/thumbnails/1.jpg)
Chapter 27 (continued)Chapter 27 (continued)
Specific Catabolic Specific Catabolic Pathways:Pathways:Carbohydrate, Lipid & Carbohydrate, Lipid & Protein MetabolismProtein Metabolism
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1.
2. 3.
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Fatty Acids and EnergyFatty 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.
C6H12O6 + 6O2
CH3(CH2)14COOH + 23O2
6CO2 + 6H2O
16CO2 +16H2OPalmitic acid
Glucose
Energy(kcal•mol-1)
Energy(kcal•g-1)
686 3.8
2,340 9.3
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• five enzyme-catalyzed reactions• cleaves carbon atoms two at a time from the carboxyl end of a fatty acid.
-Oxidation-Oxidation
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-Oxidation-Oxidation
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-Oxidation-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.
R-CH2-CH2-C-OHO
ATP CoA-SH
R-CH2-CH2-C-SCoAO
AMP 2Pi
+ +
+ +
A fatty acid
An acyl CoA
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-Oxidation-Oxidation• Reaction 2: Reaction 2: oxidation of the , carbon-carbon single bond to a carbon-carbon double bond.
R-CH2-CH2-C-SCoAO
An acyl-CoA
+FADO
HC C
C-SCoA
R H
+ FADH2
A trans enoyl-CoA
acyl-CoA dehydrogenase
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-Oxidation-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.
+ H2O
An L--hydroxyacyl-CoA
C
OH
CH2-C-SCoARH
Oenoyl-CoAhydrataseH
C CC-SCoA
R HA trans enoyl-CoA
O
C
OH
CH2-C-SCoAHR
ONAD+
R-C-CH2-C-SCoAO O
NADH H+
-Hydroxyacyl-CoA
-Ketoacyl-CoA
+
-hydroxyacyl-CoAdehydrogenase
+
+
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-Oxidation-Oxidation• Reaction 5:Reaction 5: cleavage of the carbon chain by a molecule of CoA-SH.
R-C-CH2-C-SCoA
OO
CoA-SH
R-C-SCoA
O O
CH3C-SCoA
-Ketoacyl-CoA
+
Coenzyme A
+
An acyl-CoA Acetyl-CoA
thiolase
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-Oxidation-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.
CH3(CH2)16C-SCoAO
8NAD+8CoA-SH
9CH3C-SCoAO
8FAD
8NADH8FADH2
Octadecanoyl-CoA(Stearyl-CoA)
+
+Acetyl-CoA
eight cycles of -oxidation
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Energy Yield from Energy Yield from --OxidationOxidation
• Yield of ATP per mole of stearic acid (C18). ATPStepChemical Step Happens
1
2
4
Activation (stearic acid -> stearyl CoA)
Oxidation (acyl CoA ->trans-enoyl CoA)produces FADH2Oxidation (hydroxy-
acyl CoA to ketoacyl
CoA) produces NADH +H+
Oxidation of acetyl CoAby the common metabolicpathway, etc.
Once
8 times
8 times
9 times
-2
16
24
108
TOTAL 146
Glycolysis TOTAL 36
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• IF lauric acid (1) is metabolized through -Oxidation,
• what are the products of the reaction after 3 turns of the spiral?
Challenge QuestionChallenge Question
(1)
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• Which C-18 fatty acid yields the greater amount of Energy:
• Saturated stearic acid?
• Monounsaturated oleic acid?
Confirming your knowledgeConfirming your knowledge
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Formation of Ketone bodiesFormation of Ketone bodies from lack of glucose from lack of glucose
• A little Glucose needed to fully run -Oxidation
ββ-Oxidation-Oxidation
Formation of Ketone Bodies for Energy(Low glucose levels)
headaches.. ?
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Ketone Bodies, see p. Ketone Bodies, see p. 677-8677-8
CH3-CH-CH2-COO-OH
CH3CCH2C-SCoA
O O
NADH
HS-CoA
CH3-C-CH3
O
NAD+ + H+
CH3-C-CH2-COO-
O
2CH3C-SCoAO
CO2
Acetyl-CoA Acetoacetyl-CoA
Acetoacetate -Hydroxybutyrate
AcetoneCH3-CH-CH2-COO-
OH
CH3CCH2C-SCoA
O O
NADH
HS-CoA
CH3-C-CH3
O
NAD+ + H+
CH3-C-CH2-COO-
O
2CH3C-SCoAO
CO2
Acetyl-CoA Acetoacetyl-CoA
Acetoacetate -Hydroxybutyrate
Acetone
CH3-CH-CH2-COO-OH
CH3CCH2C-SCoA
O O
NADH
HS-CoA
CH3-C-CH3
O
NAD+ + H+
CH3-C-CH2-COO-
O
2CH3C-SCoAO
CO2
Acetyl-CoA Acetoacetyl-CoA
Acetoacetate -Hydroxybutyrate
Acetone
• 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
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• for example when:• intake is high in lipids and low in carbohydrates.• diabetes is not suitably controlled.• Starvation occurs.
Ketone Bodies are Ketone Bodies are formedformed
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Challenge QuestionChallenge Question• What happens to the oxaloacetate produced
from carboxylation of phosphoenolpyruvate?
(i.e. where does it go and or where is it needed?)
?
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Protein CatabolismProtein CatabolismFigure 27.7 Overview of Protein catabolism.
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Nitrogen of Amino Nitrogen of Amino AcidsAcids• A. -NH2 groups move freely by TransaminationTransamination• Amino acids transfer amino groups to -ketoglutarate
Glutamate . . .
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Nitrogen of Amino AcidsNitrogen of Amino Acids
• B. Oxidative Deamination nitrogens to be excreted are collected in glutamate, which is oxidized to -ketoglutarate and NH4
+.
• NH4+ then enters the urea cycle.
COO-
CH-NH3+
CH2
CH2
COO-
H2O
NAD+ NADHCOO-
C=O CH2
CH2
COO-
NH4+
Glutamate -Ketoglutarate
++
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The Urea Cycle – Overview The Urea Cycle – Overview • a cyclic pathway that produces urea from CO2 and NH4
+.
For step details see p. 681-683
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The Urea Cycle p.681-682The Urea Cycle p.681-682
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(Urine)
The Urea Cycle (cont.)The Urea Cycle (cont.)
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Challenge QuestionChallenge 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?
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Challenge Question 2Challenge Question 2• What are the molecular sources of Nitrogen in Urea?
Hint: see Urea Cycle ReactionsSteps 1-2 and 3
p.681-682
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Heme CatabolismHeme 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. . .
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Final Challenge Final Challenge QuestionQuestion• Why is High bilirubin content in the
blood an indication of liver disease?