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Metabolism of Lipids I - Coggle Diagram
Metabolism of Lipids I
Fats Provide Efficient Fuel Storage
long-term (months) energy needs
slow delivery
good storage
Dietary Fatty Acids Are Absorbed in the
Vertebrate Small Intestine
Hormones Trigger Mobilization
of Stored Triacylglycerols
Lipases are activated by hormones glucagon and epinepherine.
Glycerol from Fats Enters Glycolysis
Transport or Attachment to Phospholipids Requires Conversion to Fatty Acyl-CoA
Fatty Acid Transport into Mitochondria
Fats are degraded in the cytoplasm of adipocytes
Fatty acids are transported through the blood.
Small (< 12 carbons) fatty acids diffuse freely
Larger fatty acids are transported via acyl-carnitine/carnitine transporter
Fatty Acid Oxidation Occurs in the
Mitochondria in Three Stages
Stage 1
B oxidation
Step 1
Dehydrogenation of Alkane to Alkene
on the inner-mitochondrial membrane
trans double bond
acyl-CoA dehydrogenase (AD)
Step 2
Hydration of Alkene
enoyl-CoA hydratas
trifunctional complex
Water adds
Step 3
Dehydrogenation of Alcohol
B-hydroxyacyl-CoA dehydrogenase
NAD cofactor as the hydride acceptor
Only L-isomers of hydroxyacyl CoA act as substrates
Step 4
Transfer of Fatty Acid Chain and Release of Acetyl-CoA
acyl-CoA acetyltransferase (thiolase)
• The net reaction is thiolysis of the carbon-carbon bond
Stage 2
citric acid cycle
Stage 3
generates ATP from NADH and FADH2 via the respiratory chain.
Fatty Acid Oxidation is Performed by a
Single Trifunctional Protein
Hetero-octamer
four a subunits
four B subunits
allow substrate channeling between enzymes
Associated with inner-mitochondrial membrane
Processes fatty acid chains with 12 or more carbons
Shorter chains processed by soluble enzymes in the
matrix
Oxidation of Unsaturated Fatty Acids
cis double bonds
isomerase
converts cis double bonds starting at carbon 3 to trans double bonds
reductase
reduces cis double bonds not at carbon 3
Monounsaturated fatty acids
isomerase
Polyunsaturated fatty acids
isomerase+reductase
Oxidation of Odd-Numbered Fatty Acids
Propionyl-CoA (3-carbon compound) forms during
final cycle of B oxidation of odd-numbered fatty acids.
Ketone Bodies
When oxaloacetate is depleted
Three forms of ketone bodies can leave the liver
acetone
acetoacetate
B-hydroxybutyrate
Formation of Ketone Bodies
Generating Free CoA
Degradation of HMG-CoA
as Fuel
