Lehninger Principles of Biochemistry

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Transcript Lehninger Principles of Biochemistry

David L. Nelson and Michael M. Cox
LEHNINGER
PRINCIPLES OF BIOCHEMISTRY
Sixth Edition
CHAPTER 17
Fatty Acid Catabolism
© 2013 W. H. Freeman and Company
Triacylglycerols
(fats or triglycerides)
Three fatty acids
ester-linked to a
glycerol molecule
Used as energy storage
molecules in eukaryotes
Stored in adipocytes
Advantages of using triacylglycerols for energy storage
1. Fats are highly reduced hydrocarbons with a large energy
of oxidation.
2. Fats are insoluble molecules that aggregate into droplets.
They are unsolvated and no storage mass is water.
3. Fats are chemically inert. They can be stored without fear
of unfavorable reactions.
Disadvantages of triacylglycerols as energy storage
1. Fats must be emulsified before enzymes can digest them.
2. Fats are insoluble in the blood and must be carried in the
blood as protein complexes.
Extraction of energy from fatty acids
Step 1. Oxidation of fatty acids to acetyl-CoA. This
generates NADH and FADH2.
Step 2. Oxidation of acetyl-CoA to CO2 in the citric
acid cycle. This generates NADH, FADH2 and
GTP (ATP).
Step 3. Transfer of electrons from NADH and FADH2 to O2.
This results in the synthesis of ATP.
Lipoproteins
Lipoproteins are large complexes of lipids and proteins designed to
transport lipids in the blood. The lipoproteins are classified
by particle density.
1. Chylomicrons (transport dietary cholesterol to tissues)
2. Very low density lipoprotein (VLDL) transport cholesterol
3. Intermediate density lipoprotein (IDL)
produced by the liver to
4. Low density lipoprotein (LDL)
tissues
5. High density lipoprotein (HDL) (transport cholesterol from tissues
to liver)
Molecular Structure of a Chylomicron
Utilization of stored triacylglycerols
Metabolic fate of
the glycerol
backbone of
triacylglycerols
Fatty acyl-CoA
synthetases
Fatty acid entry into mitochondria
Beta oxidation of
oleate 18:1Δ9
Beta oxidation of
linoleate 18:2Δ9,12
b-oxidation of
fatty acids with
an odd number of
carbons produces
propionyl-CoA.
Propionyl-CoA
is converted to
succinyl-CoA
for entry into
the citric acid cycle.
Ketone bodies can be formed from acetyl-CoA
resulting from b-oxidation of fatty acids.
Ketone bodies are exported from the liver to other
tissues to be used as fuel.
Starvation
increases synthesis
of ketone bodies