Chapter 17
Fat Catabolism
Fatty Acid Catabolism
Key topics: To Know
– How fats are digested in animals
– How fats are mobilized and transported in tissues
– How fats are oxidized as a source of energy
– How “ketone bodies” are produced and used
Oxidation of fatty acids is a major
energy source in many organisms
• About one-third of our energy needs comes from
dietary triacylglycerols
• About 80% of energy needs of mammalian heart and
liver are met by oxidation of fatty acids
• Many hibernating animals, such as grizzly bears, rely
almost exclusively on fats as their source of energy
• Some animals (camels) store fat as an eventual
source of water
Fats provide efficient fuel storage
• The advantage of fats over polysaccharides:
– Fatty acids carry more energy per carbon because they
are more reduced
– Fatty acids carry less water along because they are
nonpolar
• Glucose and glycogen are for short-term energy needs,
quick delivery
• Fats are for long-term (months) energy needs, good
storage, slow delivery
Fat Storage in White Adipose Tissue
Lipid Digestion
Chylomicron
Mobilization of Fat from Adipose Tissue
Guinea Pig Adipocytes
Entry of Glycerol into Glycolysis
Energetics of Glycerol as An Energy Source
Glycerol kinase
- ATP
Glycerol-3-P DH
+ NADH
3-P-Gyld DH
+ NADH
3-PGA Kinase
+ ATP
Pyr Kinase
+ ATP
Total
=
1 ATP + 2 NADH
Can GLYCEROL be FERMENTED?
Explain
Major Fatty Acid Oxidation = β-Oxidation
Occurs in the Mitochondrion
β-Oxidation
Overall Flow
One Round (a) and Further Rounds (b) of βOxidation
EOC Problem 4:
explores numbers of
round of β-oxidation.
EOC Problem 9:
Compartmentalization of
β-oxidation.
EOC Problem 3 Compares β-oxidation with the Citric Acid Cycle
Hibernating Animals Rely upon β-Oxidation for their
Sleep
EOC Problems 13, 26 and 28: Deals with Fat as Storage of
Water and Energy. Please keep in mind Prof Makemson spent
a good portion of his life in the Middle East…fat as storage of
water!!
Energetics of Oxidation of Palmitic Acid
*Assumes
1 NADH = 2.5 ATP, and 1 FADH2 = 1.5 ATP from
Respiratory Electron Transport
EOC Problems 1 and 2 deals with amount of energy stored in
fat and how long it can last?
Oxidation of Unsaturated Fatty Acids (Remember
they are cis!)
Multiple points of
unsaturation can require
energy to get them
through β-Oxidation
β-Oxidation of Odd Numbered Fatty Acids
Results in Propionyl-SCoA
Plant vs Animal
β Oxidation
Peroxisomes in
Animals – mainly
different in First Step
and Usually use >20 C
and branched chain
fatty acids.
Peroxisomes in Plants
are main fatty acid
oxidation (not in
mitochondria)
Seeds are Loaded with Fats and Oils
Arrangement of the β-Oxidation Enzymes
Eukaryotes Also have 2 Arrangements of these
Enzymes
ω-Oxidation in the ER of Liver Cells
Minor pathway in
mammals, more
important in invertebrates
ω = Omega, the
last letter in the
Greek alphabet
α-Oxidation of Branched Chain Fatty Acids Takes Place in
Peroxisomes
β-oxidation of Odd Numbered
Fatty Acids … last round
produces 1 Ac-SCoA and 1
Propionyl-SCoA
Formation of Ketone Bodies Occurs in the Liver
Isoprenes
and Steroids
Oxidation of Ketone Bodies by Non-hepatic Tissues
Requires
Glucogenic
Intermediates,
Glucose can
not be made
from Ac-SCoA
EOC Problem 16: About use of fatty acids in Diabetics.
Things to Know and Do Before Class
1. Review structure of fat, general concepts of digestion
of fat.
2. Role of glucagon to mobilize fat utilization.
3. Activation of fatty acids in cytoplasm for their oxidation
in the mitochondrion.
4. Know the steps of β-oxidation…and what is involved
for the complete oxidation of the fatty acids to CO2 and
water.
5. Know that unsaturated fatty acids are oxidized, but
energy output is different (which way?).
6. Know that other forms of fatty acid oxidation exist.
7. Know how ketone bodies are made and used.
8. EOC Problems: 1-4, 9, 10, 13, 16, 26, 28.