fat metabolism i’m not fat, i’ve just got a lot of potential energy!
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Fat Metabolism
I’m not fat, I’ve just got a lot of potential energy!
Digestion, Mobilization, and Transport
• http://courses.cm.utexas.edu/emarcotte/ch339k/fall2005/Lecture-Ch17-1/Slide2.JPG
Emulsification
• Fats are not water soluble
• Made into bile salts that are
• Absorbed as micelles in small intestines
Chylomicron Carriers
• proteins that carry fats
• stored in adipose tissue
Role of Hormones
• Can mobilize from adipose
• Release as Fatty acids
• Epinephrene and glucagon release cAMP– make fatty acids and glycerol– mobilizes fat
Animation of Process
• http://www.wiley.com/legacy/college/boyer/0470003790/animations/fatty_acid_metabolism/fatty_acid_metabolism.htm
• FUN!
Activation and Transported to Mitochondria
• FA + CoASH --> ATP = FA-SCoA + AMP + Ppi
• Driven by breakup of Ppi• Acyl CoA Synthetase• -32.5 kJ• Transported through inner mitochondrial
membrane via carnitine– uses specific acyl carnitine transporter
Carnitine
N+
CH2CH3
CH3
CH3
CH CH2
OH
CO
O
Formation of acyl carnitine
N+
CH2CH3
CH3
CH3
CH CH2
OH
CO
OCoAS C R
O
carnitine acyl CoA
N+
CH2CH3
CH3
CH3
CH CH2
O
CO
O
C
R
O
CoASH
acyl carnitine
+ +
• Can get transported across inner mitochondrial membrane
Animation of Process
• http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/carnitine/carnitine1.html
Beta Oxidation
• Breakdown of fats into – Acetyl coenzyme A --> Krebs Cycle
– FADH2 --> Oxidative Phosphorylation
– NADH--> Oxidative Phosphorylation
• Breaks off two carbons at a time to acetyl CoA– Remaining goes another round
Reactions DiagramCH2R CH2 CH2 C
O
S-CoA
FAD
FADH2
CHR CH CH2 C
O
S-CoA
Acyl-CoA Dehydrogenase
acyl-CoA
beta-enoyl CoA
OH2
enoyl-CoA hydratase
NAD+
NADHbeta-hydroxyacyl-CoA
dehydrogenase
CH2R C CH2 C
O
S-CoA
O
thiolaseHSCoA
CH3 C
O
S-CoA
beta-ketoacyl CoA
acetyl CoA
CH2 C
O
S-CoAR
CH2R CH CH2 C
O
S-CoA
OH
beta hydroxyacyl CoA
Reactions of Beta Oxidation Acyl-CoA Dehydrogenase
CH2R CH2 CH2 C
O
S-CoA
FAD FADH2
Acyl-CoA Dehydrogenase
acyl-CoA beta-enoyl CoA
CHR CH CH2 C S-CoA
O
– Puts in a ß double bond• Oxidizes C-C bond to double bond
– Produces FADH2
Reactions of Beta oxidationEnoyl CoA Hydratase
CHR CH CH2 C
O
S-CoA
beta-enoyl CoA
OH2
enoyl-CoA hydratase
CH2R CH CH2 C
O
S-CoA
OH
beta-hydroxyacyl CoA
• adds water– forms ß-hydroxy product
Reactions of Beta Oxidation ß-hydroxylacyl-CoA dehydrogenase
CH2R CH CH2 C
O
S-CoA
OH
beta-hydroxyacyl CoA
NAD+ NADH
beta-hydroxyacyl-CoAdehydrogenase
CH2R C CH2 C
O
S-CoA
O
beta-ketoacyl CoA
• oxidizes secondary alcohol to ketone– Oxygen-containing group
– Produces NADH
Reactions of Beta Oxidation Acyl-CoA acetyltransferase (thiolase)
CH2R C CH2 C
O
S-CoA
O
thiolase
HSCoA
CH3 C
O
S-CoA
beta-ketoacyl CoA
acetyl CoA
CH2 C
O
S-CoAR
acyl CoA
• Uses another CoA• Produces Acetyl CoA• Acyl CoA can go another round
Overall Per Beta Oxidation cycle
• 1 FADH2…………………………1.5 ATP
• 1 NADH………………………….2.5 ATP• 1 Acetyl CoA to Krebs
– 3 NADH X 2.5 ATP / NADH………7.5 ATP
– 1 FADH2…………………………….1.5 ATP
– 1 GTP………………………………..1.0 ATP
Total = 14.0 ATP
Beta Oxidation on 16 C fatty Acid
CH2 CO
O
CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2
CH2CH3
Beta Oxidation on 16 C fatty Acid
CH2 CO
O
CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2
CH2CH3
12
34567
1 2 3 4 5 6 78
• 7 rounds of Beta oxidation (bottom numbers)• Form 8 acetyl Co A (top numbers)
Beta Oxidation on 16 C fatty Acidtotals
• 7 rounds of beta oxidation7 rounds X FADH2 X 1.5 ATP = 10.5 ATP
round FADH2
7 rounds X NADH X 2.5 ATP = 17.5 ATP round NADH
8 acetyl CoA8 Krebs
8 Krebs X 3 NADH X 2.5 ATP = 60 ATP Krebs NADH
8 Krebs X FADH2 X 1.5 ATP = 12 ATP Krebs FADH2
8 Krebs X GTP X 1 ATP = 8 ATPKrebs GTP
1 ATP used to activate = - 1 ATP
Total 107 ATP
Unsaturated Fat Metabolism
• special enzymes needed to convert cis bonds in fatty acids to trans bonds
Regulation of Fat Metabolism
• Transport is rate-limiting
• Regulation of carnitine acyl transferase– off by fat synth products– high NADH
Ketone Bodies
• Starvation causes accumulation of acetyl CoA– not enough carbohydrates to keep Kreb’s Cycle
going– acetyl CoA forms acetoacetate, b-
hydroxybutyrate, and acetone.
• http://www.biocarta.com/pathfiles/ketonebodiesPathway.asp
Diabetes and Ketone Bodies
• When there is not enough insulin in the blood and it must break down fat for its energy.
• Ketones build up in the blood and then spill over into the urine so that the body can get rid of them. Acetone can be exhaled through the lungs. This gives the breath a fruity odor. Ketones that build up in the body for a long time lead to serious illness and coma. (Diabetic ketoacidosis)
Comparison of Fat Metabolism per gram and CHO per gram
• Fats provide about 9 kilocalories per gram and carbohydrates provide about 4 kilocalories per gram.
• Using nutritional units, that is 9 Calories/gram for fats and 4 Calories/gram for carbohydrates.
• CHO provide energy more quickly• Fats are good fuel for endurance events, but
not sprints
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