2 The body fat is our major source of stored energy.
Our adipose tissue is made of fat cells adipocytes.
A typical 70 kg (150 lb) person has about 135000 kcal of energy stored as fat 24000 kcal as protein 720 kcal as glycogen reserves and 80 kcal as blood glucose.
The energy available from stored fats is about 85 of the total energy available in the body.
3 Digestion of Triacylglycerols
In the digestion of fats (triacylglycerols)
Bile salts break fat globules into micelles in the small intestine.
Pancreatic lipases hydrolyze ester bonds to form monoacylglycerols and fatty acids which recombine in the intestinal lining.
Lipoproteins form and transport triacylglycerols to the cells of the heart muscle and adipose tissues.
Brain and red blood cells cannot utilize fatty acids because fatty acids cannot diffuse across the blood-brain barrier and red blood cells have no mitochondria where fatty acids are oxidized. (Glucose and glycogen are the only source of energy for the brain and red blood cells.)
4 Digestion of Triacylglycerols 5 Fat Mobilization
Breaks down triacylglycerols in adipose tissue to fatty acids and glycerol.
Occurs when hormones glucagon and epinephrine are secreted into the bloodstream and bind to the receptors on the membrane of adipose cells activating the enzymes within the fat cells that begin the hydrolysis of triacylglycerols.
Fatty acids are hydrolyzed initially from C1 or C3 of the fat.
Triacylglycerols 3H2OGlycerol 3Fatty acids
6 Metabolism of Glycerol.
Using two steps enzymes in the liver convert glycerol to dihydroxyacetone phosphate which is an intermediate in several metabolic pathways including glycolysis and gluconeogenesis.
1st step glycerol is phosphorylated using ATP to yield glycerol-3-phosphate.
2nd step the hydroxyl group is oxidized to yield dihydroxyacetone phosphate.
The overall reaction for the metabolism of glycerol
Glycerol ATP NAD Dihydroxyacetone phosphate ADP NADH H
7 Fatty Acid Activation
Fatty acid activation
Allows the fatty acids in the cytosol to enter the mitochondria for oxidation.
Combines a fatty acid with CoA to yield fatty acyl CoA that combines with carnitine.
8 Fatty Acid Activation
Fatty acyl-carnitine transports the fatty acid into the matrix.
The fatty acid acyl group recombines with CoA for oxidation.
9 Fatty Acid Activation
Fatty acid activation is complex but it regulates the degradation and synthesis of fatty acids.
10 Beta-Oxidation of Fatty Acids
In reaction 1 oxidation
Removes H atoms from the and carbons.
Forms a trans CC bond.
Reduces FAD to FADH2.
11 Beta-Oxidation of Fatty Acids
In reaction 2 hydration
Adds water across the trans CC bond.
Forms a hydroxyl group (OH) on the carbon.
12 Beta ()-Oxidation of Fatty Acids
In reaction 3 a second oxidation
Oxidizes the hydroxyl group.
Forms a keto group on the carbon.
13 Beta ()-Oxidation of Fatty Acids
In Reaction 4 acetyl CoA is cleaved
By splitting the bond between the and carbons.
To form a shortened fatty acyl CoA that repeats steps 1 - 4 of -oxidation.
14 Beta ()-Oxidation of Myristic (C14) Acid 15 Beta ()-Oxidation of Myristic (C14) Acid (continued) 7 Acetyl CoA 6 cycles 16 Cycles of -Oxidation
The length of a fatty acid
Determines the number of oxidations and
The total number of acetyl CoA groups.
Carbons in Acetyl CoA -Oxidation Cycles
Fatty Acid (C/2) (C/2 1)
12 6 5
14 7 6
16 8 7
18 9 8
17 -Oxidation and ATP
Activation of a fatty acid requires
One cycle of oxidation of a fatty acid produces
1 NADH 3 ATP
1 FADH2 2 ATP
Acetyl CoA entering the citric acid cycle produces
1 Acetyl CoA 12 ATP
18 ATP for Lauric Acid C12
ATP production for lauric acid (12 carbons)
Activation of lauric acid -2 ATP
6 Acetyl CoA
6 acetyl CoA x 12 ATP/acetyl CoA 72 ATP
5 Oxidation cycles
5 NADH x 3ATP/NADH 15 ATP
5 FADH2 x 2ATP/FADH2 10 ATP
Total 95 ATP
19 Oxidation of Unsaturated Fatty Acids.
Oxidation of monounsaturated fatty acyl-CoA requires additional reaction performed with the help of the enzyme isomerase.
Double bonds in the unsaturated fatty acids are in the cis configuration and cannot be acted upon by enoyl-CoA hydratase (the enzyme catalyzing the addition of water to the trans double bond generated during ß-oxidation.
Enoyl-CoA isomerase repositions the double bond converting the cis isomer to trans isomer a normal intermediate in ß-oxidation.
20 Oxidation of polyunsaturated fatty acids.
Requires two additional reactions and a second enzyme reductase in addition to isomerase.
NADPH-dependent 24-dienoyl-CoA reductase converts trans-2 cis-4-dienoyl-CoA intermediate into the trans-2-enoyl-CoA substrate necessary for ß-oxidation.
21 Oxidation of odd-chain fatty acids.
Odd-carbon fatty acids are oxidized by the same pathway as even-carbon acids until three-carbon propionyl-CoA is formed.
After that three additional reactions are required involving three enzymes.
Propionyl-CoA is carboxylated by propionyl-CoA carboxylase (with the cofactor biotin) to form the D stereoisomer of methylmalonyl-CoA (The formation of the carboxybiotin intermediate requires energy from ATP).
D-methylmalonyl-CoA is changed into L-methylmalonyl-CoA by methylmalonyl-CoA epimerase.
L-methylmalonyl-CoA undergoes an intramolecular rearrangment to form succinyl-CoA which enters the citric acid cycle. This rearrangment is catalyzed by methylmalonyl-CoA mutase which requires coenzyme B12 derived from vitamin B12 (cobalamin).
22 (No Transcript) 23 (No Transcript) 24 (No Transcript) 25 (No Transcript) 26 (No Transcript) 27 (No Transcript) 28 (No Transcript) 29 (No Transcript) 30 Overview of Metabolism
Catabolic pathways degrade large molecules.
Anabolic pathway synthesize molecules.
Branch points determine which compounds are degraded to acetyl CoA to meet energy needs or converted to glycogen for storage.
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