Fatty acids undergo beta-oxidation in the mitochondria to break them down into acetyl-CoA units for energy production. There are four main steps: 1) activation by adding CoA, 2) transport into the mitochondrial matrix using carnitine, 3) repeated oxidation reactions that remove two-carbon acetyl-CoA units, and 4) regulation by malonyl-CoA and feedback inhibition when ATP levels are high. Unsaturated and odd-numbered fatty acids require additional enzymes for isomerization or conversion into intermediates that can enter the citric acid cycle.

1. Fatty Acid Catabolism
(Oxidation of Fatty Acids):
1.Saturated fatty acids
2.Unsaturated fatty acids
3.Ketogenesis

2. Overview of Fatty Acid Metabolism

3. Triacylglycerols Are a Major Form of Stored Energy
in Animals
*triacylglycerol lipase
(also called hormone-sensitive lipase)

4. Degradation of Dietary Fatty Acids
Occurs Primarily In the Duodenum Page 699

5. Page 700

6. Fatty acid oxidation
3 steps to break down fatty acids to make energy
1.Fatty acid must be activated: bound to
coenzyme A
2.Fatty acid must be transported into
mitochondrial matrix: uses a shuttle mechanism
3.Fatty acid repeatedly oxidized, cycling thru 4
reactions: produces Acetyl CoA, FADH2, &
NADH

7. Reactions of the
fatty acid spiral for
an
18:0 fatty acid
(stearic acid).
Repeats as a
spiral because
each section
becomes shorter
by 2 carbons

8. Fatty Acid oxidation
• Major Pathway
– β-oxidation
• Minor Pathway
– α-oxidation
(branch-chain FA,e.g. Phytanic acid)
– ω-oxidation

9. β-oxidation Pathway
• Oxidation of fatty acids takes place in
mitochondria where the various enzymes
for fatty acid oxidation are present close to
the enzymes of the electron transport
chain.
• Fatty acid oxidation is a major source of
cell ATP
• Oxidation of FAs occur at the β-carbon
atom resulting in the elimination of the two
terminal carbon atoms as acetyl CoA
leaving fatty acyl CoA which has two
carbon atoms less than the original fatty
acid.
• β-oxidation has 4 steps:
1-Dehydrogenation (FAD-dependent)
2- Hydration
3-Dehydrogenation (NAD-dependent)
4-Cleavage (Remove 2C as acetyl CoA)

10. Activation of
Fatty Acids

12. Summary of fatty acid activation:
fatty acid + ATP  acyl-adenylate + PPi
PPi  2 Pi
acyladenylate + HS-CoA  acyl-CoA + AMP
Overall:
fatty acid + ATP + HS-CoA  acyl-CoA + AMP + 2 Pi
Thiokinase

13. The longer chain F.A.s cannot diffuse across
mitochondrial membrane - must be transported.
Uses a carrier protein:
carnitine (derivative of amino acid lysine)
Found in red meats & dairy products,
can also be synthesized by the body.
Reminder: an acyl group is
derived from a carboxylic acid
(like a fatty acid) with its
–OH group removed

15. Transport into the Mitochondrion
(Carnitine-Acylcarnitine
Translocase)

16. Carnitine Shuttle

17. Long chain fatty acids are transported across the inner
mitochondrial membrane in the form of acyl carnitine.
People with
low carnitine
levels often
have lipid
deposition in
the muscles,
become
irritable &
weak.
Severe
disorders can
be fatal!
Companies
selling
nutritional
products
promote
carnitine as
an important
dietary
supplement.

18. b-oxidation
• Mitochondrial matrix
• Oxidizes fatty acyl CoA’s at the
b carbon
• Sequentially cleaves off acetyl
CoAs
• Acetyl CoA is processed
through Krebs and ETC

19. Page 701
b oxidation

20. Regulation of fatty acid β-
oxidation
1- The level of ATP in the cell :If it is high in the cell, the rate of β-
oxidation will decrease (Feed back inhibition)
2- Malonyl-CoA
* (which is also a precursor for fatty acid synthesis) inhibits Carnitine
Palmitoyl Transferase I and thus, inhibits β-oxidation
* Malonyl-CoA is produced from acetyl-CoA by the enzyme Acetyl-CoA
Carboxylase

21. Reaction Steps
Oxidation
Hydration
Oxidation
Cleavage

22. Reaction 1: Oxidation
Three isozymes of
acyl-CoA
dehydrogenase:
Long chain (12-18C)
Medium chain (4-14C)
Short chain (4-8C)

23. Reaction 2:
hydration

24. Reaction 3:
oxidation

25. Reaction 4: thiolytic
cleavage

26. Beta Oxidation
Fatty Acyl CoA
Dehydrogerase

27. Beta Oxidation
Enoyl CoA Hydratase

28. Beta Oxidation
Beta Hydroxyacyl CoA
Dehydrogenase

29. Beta Oxidation
Thiolase

30. Beta Oxidation

31. Beta Oxidation

32. β Oxidation of Saturated
Fatty Acid (cont’)
• Oxidation
– Acyl CoA dehydrogenase
• Forms trans double bond between C2 and C3
• FADH2 produced electrons enter ETC
– Electron-transferring flavoprotein (ETF)
– ETF:ubiquinone reductase
– Ubiquinone reduced to ubiquinol (of ETC)
• Three forms
– Long chain works on Acyl Co A containing 18 – 12 carbons
– Medium chain 14 -4 carbons
– Short 4 – 6 carbons
• Hydration
– Enoyl CoA hydratase
• Stereospecific hydration of double bond
• Oxidation
– L-3-hydroxyacyl CoA dehydrogenase
• C 3 hydroxyl oxidized to keto group
• Thiolysis
– β-ketothiolase
• Co A cleaves molecule at C3 releasing Acetyl Co A

33. 2 Systems for b-
oxidation
• ≥ 12 carbons:
• TFP – last 3 enzymes
in multienzyme complex
• < 12 carbons
• 4 soluble matrix
enzymes

34. • Palmitate weighs ~256 g/mol (about 42% more than
glucose)
• Oxidation yields 108 ATPs, versus 32ish for glucose (about
340% more)

35. Fatty Acid Oxidation Is an Important Source of
Metabolic Water for Some Animals
1 acetyl -CoA: 1FADH2+3NADH+1ATP=1x1.5+3x2.5+1=10

36. Beta Oxidation

37. Monounstaurated
Fatty Acids
• Need one extra
enzyme
• Converts double bond
1

38. Oxidation of Unsaturated
Fatty Acid
• Slightly more complicated Requires additional enzymes
• Oxidation of unsaturated FAs produce less energy than that
of saturated FAs (because they are less highly reduced,
therefore, fewer reducing equivalents can be produced from
these structures)

40. Oleoyl CoA undergoes three cycles of β-oxidation like normal
saturated fatty acids to yield 3 molecules of acetyl CoA and
results in the formation of 12-carbon fatty acyl-CoA with a cis
double bond now between carbon 3 and 4. This product is
known as cis-Δ3-Dodecenoyl-CoA.
The above product formed has a cis double bond and cannot
further participate in β-oxidation. Thus by the action of Δ3,Δ2-
enoyl-CoA isomerase, cis-Δ3-Dodecenoyl-CoA is converted
to trans-Δ2-Dodecenoyl-CoA. This is the significance of
the isomerase enzyme in the β-oxidation of unsaturated fatty
acids.
trans-Δ2-Dodecenoyl-CoA now is acted upon by the enzymes
of β-oxidation pathway in five continuous cycles to yield
another 6 molecules of acetyl CoA.
The acetyl-CoA molecules now enter the Kreb’s cycle.

41. Unsaturated fatty acids, while
prominent in our diets, are more
complicated to metabolize than
saturated ones. In addition to the
reactions required for the degradation
of saturated fatty acids, the
degradation of unsaturated fatty acids
calls for two supplementary enzymes:
an isomerase and a reductase.

42. cis-Δ3-enoyl CoA is not a substrate for acyl CoA
dehydrogenase. As seen in the picture, there is a double
bond between C3 and C4 which prevents a double bond from
forming between C2 and C3. This obstacle in degradation is
overcome by shifting the position and configuration of the cis-
Δ3 double bond to a trans-Δ2 double bond; this new reaction
is facilitated by cis-Δ3-Enoyl CoA isomerase. Now that the
double bond is between C2 and C3, the rest of the reactions
relevant to saturated fatty acid oxidation can be done on
trans-Δ2-enoyl CoA.

43. Polyunsaturated Fatty Acids
• Need two extra enzymes
• Reduce conjugated double bonds to a
single double bond
1
2
1

44. Polyunsaturated Fats
Both an
isomerase
and a
reductase
are
necessary.

48. β Oxidation of Unsaturated Fatty
Acids
• The enzymes required to oxidize an unsaturated
fatty acid are determined by the location of the
double bond.
– Fatty acids with a double bond beginning at an odd
number carbon.
• E.g. C3 – C4
• Isomerase ONLY
– cis-Δ 3 Enoyl Co A isomerase
– Fatty acids with a double bond beginning at an even
number carbon.
• E.g.C4 – C5
• Reductase AND Isomerase
– 2,4-dienoyl Co A reductase
– cis-Δ 3 Enoyl Co A isomerase

49. cis-Δ 3 Enoyl Co A isomerase
• Shifts the position
of a “odd
numbered
carbon” double
bond in a fatty
acid from C3=C4
to C2=C3.
This molecule is NOT a
substrate for acyl Co A
dehydrogenase
because of the location
of the double bond.

51. 2,4-dienoyl Co A reductase
• Uses
NADPH
to
reduce
“even
number”
double
bond

52. Excess polyunsaturated fatty acids (ones with more than one
double bond) are degraded via beta-oxidation and are important
to humans as precursors for signal molecules. There is another
obstacle to be overcome when dealing with polyunsaturated
fatty acids, however, which can be discerned by looking at the
oxidation of the 18-carbon polyunsaturated fatty acid linoleate
(pictured). Linoleate has cis-Δ9 and cis-Δ12 double bonds; when
the cis-Δ3 double bond is formed after 3 rounds of beta-
oxidation, it is converted into a trans-Δ2 double bond by the
same isomerase mentioned in the palmitoleate degradation.
After another round of beta-oxidation, the acyl CoA produced
contains a cis-Δ4 double bond. When this species is
dehydrogenated by acyl CoA dehydrogenase it yields a 2,4-
dienoyl intermediate.

53. This intermediate is not a substrate for the next enzyme in
the beta-oxidation pathway, so 2,4-dienol CoA reductase is
employed to convert the intermediate into trans-Δ3-enoyl
CoA. 2,4-dienol CoA reductase does this by using NADPH
to reduce the 2,4-dienoyl intermediate to trans-Δ3-enoyl
CoA. cis-Δ3-enoyl CoA isomerase can then convert the
trans-Δ3 into the trans-Δ2 form, which is an acceptable
intermediate in the beta-oxidation pathway.

54. Linolenic acid is an unsaturated fatty acid with two cis double bonds. Like
saturated fatty acids the polysaturated fatty acid undergoes three cycles of β-
oxidation to yield three molecules of acetyl CoA along with a 12 carbon
chain fatty acyl-CoA with cis double bonds at position 3 and 6 (cis-Δ3,cis-Δ6).
Since the mitochondrial enzymes cannot break down cis double bonds, Δ3,Δ2-
enoyl-CoA isomerase converts it to (trans-Δ2,cis-Δ6) fatty acyl-CoA. The
latter product now undergoes one more cycle of β-oxidation to yield
the fourth molecule of acetyl CoA and the remaining product left behind
is cis-Δ4 fatty acyl-CoA.
By the action of acyl-CoA dehydrogenase, the first step of β-oxidation is
achieved, resulting in formation of a double bond at position 2 forming the
product (trans-Δ2,cis-Δ4) fatty acyl-CoA. The newly formed product is now
acted upon by the enzyme 2,4-dienoyl CoA-reductaseto form trans-Δ3 fatty
acyl-CoA which on further action by enoyl-CoA isomerase gives trans-
Δ2 fatty acyl-CoA.
trans-Δ2 fatty acyl CoA now undergoes four cycles of β-oxidation to yield
another five molecules of acetyl CoA.
The acetyl-CoA molecules now enter the Kreb’s cycle.

55. Oxidation of Odd Numbered
Fatty Acid
• Requires three additional extra
reactions.
• Odd numbered lipids are present
in plants and marine organisms
• Fatty acids with odd number of
carbon atoms are also oxidized
by the same process β-oxidation
as even chain FAs, removing 2
carbons as acetyl CoA in each
round of the oxidative process
BUT the final round of β-
oxidation of a fatty acid with an
odd number of C atoms yields
acetyl-CoA & propionyl-CoA
(3C).

56. Oxidation of Odd-Chain Fats
Propionyl-CoA is
the last piece
released.
Propionyl-CoA
undergoes
conversion to
succinyl-CoA, which
enters TCA.

57. Odd-numbered Fatty Acids
• Left with 3 carbons
• Add inorganic carbon
• Convert to succinate
• Throw into Krebs Cycle

61. malic enzyme
Succinyl-CoA
Page 713

62. β Oxidation Odd-Numbered Fatty
Acids
• Propionyl Co A (3 carbons) is the result of β oxidation of odd-numbered
fatty acids. Rearrangement of 3 carbons of Propionyl Co A leads to
these carbons entering Kreb’s cycle following
– carboxylation by propionyl CoA carboxylase
• Uses biotin as coenzyme
– isomerization by methylmalonyl CoA mutase
• Uses vitamin B12 (Cobalamin)

63. Vitamin B12 (Cobalamin)
• Corrin ring with central cobalt
atom
– Cobalt forms 6 coordinate bonds
• 4 to N of pyrrole units
• 1 to 5’deoxyadenosyl unit
• 1 to dimethylbenzimidazole unit
(usual) or cyano, methyl or other
ligand.
• Used in
– Intramolecular interactions
– Methylations
• Synthesis of methionine
• Reduction of ribonucleotides into
deoxyribonucleotides.
• Two enzymes in mammals use
this coenzyme
– methylmalonyl CoA mutase
– Methionine synthase
(aka homocysteine
methyltransferase)
• Synthesis of methionine

64. propionyl CoA carboxylase
• Carboxylates
propionyl CoA to D-
Methylmalonyl CoA
• Requires
– ATP
– Biotin

65. methylmalonyl CoA mutase
• Isomerization of D-methylmalonyl Co A to L-methylmalonyl
Co A
• Exchanges H and CO-S-CoA using homolytic cleavage
reaction (one eletron on Co3+, other electron on C of CH2۬·
radical)
• Requires
– Vitamin B12
• Forms
– CH2۬· radical
• Abstracts a H from substrate.

66. methylmalonyl CoA mutase
(Cont’)

68. Pernicious Anemia
• B12 is produced only by several genera of bacteria, obtained
from animal food
• daily requirement is about 2-3 mg/day
• Gastric mucosa produces a protein called intrinsic factor
• Lack of intrinsic factor results in impaired B12 absorption,
pernicious anemia, death in 1-3 years
• Original treatment (1920’s) was ½ lb. of raw liver daily
• Concentrated liver juice (yum) became available in 1928
• B12 isolated in 1948, synthesized in 1973
• Now treated with large doses (several mg) B12
• Sources: fish, meat, poultry, eggs, milk, especially liver and
mollusks (clams, oysters, etc.)

69. (ACC = Acetyl CoA Carboxylase)
Regulation

70. Other Ways to Oxidize Fatty Acids
• Peroxisomal b-oxidation
• Branched-chain -oxidation
• -oxidation

72. Omega oxidation
• Minor pathway taking place in Microsomes.
• Need NADH and Cytochrome P-450.
• Omega oxidation is defective and dicarboxylic
acids ( 6C and 8C acids ) are excreted in urine
causing dicarboxylic aciduria.
• Omega oxidation occurs from omega end.

73. Ω-Oxidation
•ER of vertebrates
•Medium chain FAs

78. ω-Oxidation Pathway
• ω-oxidation is a minor
pathway and occurs in
the endoplasmic
reticulum of many
tissues rather than the
mitochondria, the site of
β-oxidation.
• This process occurs
primarily with medium
chain FAs of adipose
tissue which are
mobilized to the liver
under conditions of
ketosis

79. -oxidation Page 717

80. ω-oxidation is a subsidiary
oxidation pathway of β-
oxidation for the fatty acids
when the β-oxidation is
blocked.

81. Omega oxidation is a substitute for beta oxidation only in the
extreme case where, for whatever reason, beta oxidation isn't
working or is otherwise limited.
Consider the following scenario: beta oxidation is knocked out
at one or more points or knocked down so that there is a
bottleneck.
Omega oxidation then fulfills two distinct roles:
What can a cell do to process fatty acids or get a bare
minimum of energy if beta oxidation is blocked? It resorts to
omega oxidation, which allows it to gain a reducing equivalent
by oxidizing the omega carbon three times. It's a sub-optimal
solution, since beta oxidation will yield much more NAD(P)H
than omega oxidation, but it beats starving.
The resulting dicarboxylates from omega oxidation are water
soluble, which means that they can be more easily excreted.

82. Consider a second scenario: there is a
shortage of carnitine or carnitine
acyltransferase, causing transport from
the cytoplasm to the mitochondria to be
bottlenecked. In that case, since omega
oxidation occurs in the endoplasmic
reticulum rather than in the
mitochondrion as beta oxidation does,
omega oxidation can be used to reduce
the accumulation of fatty acids in the cell.

83. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3832743/
The biological significance of ω-oxidation of fatty acids

84. • Branched chain FAs with branches at odd-number
carbons are not good substrates for b-oxidation
 -oxidation is an alternative
• Phytanic acid -oxidase decarboxylates with
oxidation at the alpha position
 b-oxidation occurs past the branch
Branched-chain -oxidation

85. α-Oxidation Pathway
• α-oxidation occurs in brain
tissue in order to oxidize short
chain FAs
• In α-oxidation, there is one
carbon atom removed at time
from α position
• It does not require CoA and
does not generate high- energy
phosphates
• This type of oxidation is
significant in the metabolism of
dietary FAs that are methylated
on β-carbon e.g. phytanic acid
(peroxisomes)

86. -oxidation
Herbivores consume a lot of chlorophyll. Chlorophylls have a
long hydrophobic tail. Those tails are split off as part of
digestion to form phytanates.

87. -oxidation
(Peroxisomes)
Phytanates have b-
methyl groups
Can’t do b-oxidation
Dietary phytanates
•Dairy
•Fish
•Animal fats

96. • Removing carbon atoms one at a time
• From the carboxyl end .
• Important in brain.
• Does not need activation.
• Occurs in the endoplasmic reticulum
• Does not require CoA,
• Does not generate energy.
• Alpha- oxidation is mainly used for Branch chain fatty
acids E.g. Phytanic acid.
• It is derived from milk and animal fat.

99. ‧Peroxisomes that carry out flavin-
dependent oxidations, regenerating
oxidized flavins by reaction with O2 to
produce H2O2
• Similar to mitochondrial b-oxidation, but
initial double bond formation is by acyl-
CoA oxidase
• Electrons go to O2 rather than e- transport
• Fewer ATPs result
Peroxisomal b-Oxidation

100. Peroxisomes
• b-Oxidation also occurs in peroxisomes (major site in
plants)

101. Very Long or Branched Chain
Predominantly in the
peroxisomes.
Similar, but not
identical, chemistry,
using several
auxiliary enzymes.

102. Peroxisomes Also Oxidize Fatty
Acids
• Peroxisomes oxidize long chain fatty acids to octanoyl CoA.
• Electrons transfered to O2 yielding H2O2
– H2O2 detoxified by catalase.
• Peroxisomes contain isozymes of the mitochondrial
enzymes
• Zellweger syndrome is due to abnormal function of
peroxisomes.

103. Catalase
Glucose
Acyl CoA
Dehydrogenase
Acyl CoA
Oxidase

104. Peroxisomes oxidize very long chain fatty acids
• Very long chain acyl-CoA synthetase facilitates the oxidation of
very long chain fatty acids (e.g., C20, C22)
• These enzymes are induced by high-fat diets and by
hypolipidemic drugs such as Clofibrate
• FAD is e- acceptor for peroxisomal acyl-CoA dehydrogenase,
which catalyzes the 1st oxidative step of the pathway
• Within the peroxisome, FADH2 generated by fatty acid oxidation is
reoxidized producing hydrogen peroxide:
FADH2 + O2  FAD + H2O2
• The peroxisomal enzyme Catalase degrades H2O2:
2H2O2 2H2O + O2
• These reactions produce no ATP
• ß-oxidation in the peroxisomes ends at octanoyl-CoA (C 8). It is
subsequently removed from the peroxisomes in the form of
octanoyl and acetylcarnitine and both are further oxidized in
mitochondria.

105. Contrary to mitochondrial β-oxidation,
polyunsaturated fatty acids are well
oxidized in peroxisomes and slowly
oxidized in mitochondria. Some of
these acids can even inhibit the fatty
acid β-oxidation in mitochondria.

106. In animal cells peroxisomes as well as mitochondria
are capable of degrading lipids via beta-oxidation.
Nevertheless, there are important differences
between the two systems.
1) The peroxisomal and mitochondrial beta-oxidation
enzymes are different proteins.
2) Peroxisomal beta-oxidation does not degrade fatty
acids completely but acts as a chain-shortening
system, catalyzing only a limited number of beta-
oxidation cycles.
3) Peroxisomal beta-oxidation is not coupled to
oxidative phosphorylation and is thus less efficient
than mitochondrial beta-oxidation as far as energy
conservation is concerned.

107. 4) Peroxisomal beta-oxidation is not
regulated by malonyl-CoA and--as a
consequence--by feeding as opposed to
starvation.
5) Peroxisomes are responsible for the beta-
oxidation of very long chain (> C20) fatty
acids, dicarboxylic fatty acids, 2-methyl-
branched fatty acids, prostaglandins,
leukotrienes, and the carboxyl side chains of
certain xenobiotics and of the bile acid
intermediates di- and trihydroxycoprostanic
acids.

108. Long and medium chain-length unsaturated and saturated
fatty acids are well accepted as substrates by mitochondrial
and peroxisomal β-oxidations. There are, however, a set of
fatty acids and their derivatives which in mammals are
practically β-oxidized only by the peroxisomal pathway. These
compounds include long-chain dicarboxylic and very long-
chain monocarboxylic fatty acids. Others are certain
leukotriens and prostaglandins, carboxylic derivatives of
some xenobiotics, isoprenoid-derived fat soluble
vitamins, and pristanic acid, a product of the α-oxidation
of phytanic acid. These various compounds with long
aliphatic carbon chain, which are often poorly soluble in water,
are transformed to more polar metabolites in peroxisomal β-
oxidation thus facilitating their elimination.

109. Catalases
• Once again, a heme-containing enzyme
• Overall reaction: 2 H2O2 ⇄ O2 + 2 H2O
• First step: produces porphyrin cation radical
• Second step: HOOH acts as electron donor to produce O2 and
return enzyme to resting state.

110. Plants don’t store
much fat, but
seeds often do.

113. Ketone Body Generation
• During fasting or carbohydrate starvation,
oxaloacetate in the liver is used for
gluconeogenesis.
• Acetyl-CoA then doesn’t enter Krebs cycle.
• Acetyl-CoA converted in mitochondria to
ketone bodies,
• Ketone bodies are transported in the blood to
other cells
• Converted back to acetyl-CoA for catabolism
in Krebs cycle, to generate ATP.

114. Ketone bodies
Made in the
mitochondrial
matrix of liver
cells.

115. Ketone Bodies

116. Ketone Bodies

119. b-oxidation in
reverse

127. Acetoacetate “re”converted into 2
Acetyl CoA molecules in Two Steps
• Ketone bodies are
released from liver
because liver cells lack
this CoA transferase.

128. Ketone Bodies
• formed during fasting or diabetes from the Acetyl CoA produced during β
oxidation of fatty acids.
• Ketone bodies are Acetoacetate, D-3-hydroxybutyrate, and acetone found in the
blood.
• Synthesized in the liver
– 1. 3-ketothiolase
– 2. hydroxymethylglutaryl CoA synthase
– 3. hydroxymethylglutaryl CoA cleavage enzyme
– 4. D-3-hydroxybutyrate dehydrogenase
– 5* acetoacetate spontaneously decarboxylates to form acetone
HMG

129. Diabetic Ketoacidosis
• Primarily in Type 1 (insulin-dependent)
• Low insulin = low glucose transport into
cells
• Liver thinks it’s starving
• Ketone body production ramps up
• Blood pH drops into danger zone

130. Page 565
Ketone Bodies & Diabetes

131. Large Amounts of Ketone Bodies Are Produced
in Diabetes Mellitus
Type I diabetes(IDDM; insulin-dependent diabetes mellitus)
Type II diabetes(NIDDM; non-insulin-dependent diabetes mellitus)
*glucose transporter
*insulin resistance

133. • Malonyl CoA inhibits
• CPT-I, thus preventing the entry of long-chain acyl groups into
the mitochondrial matrix.
• Therefore, when fatty acid synthesis is occurring in the cytosol
(as indicated by the presence of malonyl CoA), the newly made
palmitate cannot be transferred into the mitochondria and
degraded.
• Fatty acid oxidation is also regulated by the acetyl CoA to CoA
ratio: As the ratio increases, the thiolase reaction decreases.

134. • Sources of carnitine:
• Carnitine can be obtained from the diet,
primarily in meat products.
• Carnitine can synthesized from lysine and
methionine in the liver and kidney..

135. ATP production from Fatty Acid Oxidation
How does energy output compare to glucose
oxidation?
All turns (except last) of the F.A. spiral make:
one NADH & one FADH2
One Acetyl CoA forms at each turn,
& two Acetyl CoA form at last step.
These are processed in Krebs cycle, E.T.C. and
oxidative phosphorylation.

136. Hibernating Animals Rely upon
β-Oxidation for their Sleep

138. An 18C stearic fatty acid will create:
9 acetyl CoA, which form 90 ATP
8 FADH2 which form 12 ATP
& 8 NADH which form 20 ATP
Total = 122 ATP (-2 ATP for F.A. activation)
=120 ATP!
ATP production from
Fatty Acid Oxidation

139. Each round of the TCA produces 1 ATP directly, 3
NADH and 1 FADH2.
Different text books have different yields of ATP from
the oxidation of each NADH and FADH2. Many
books say the yield is 3 ATP for each NADH oxidized
and 2 ATP for each FADH2 oxidized. So, using those
values, you would produce 12 ATP for each acetyl-
CoA oxidized.
Other books have more correct values of 2.5 and
1.5. Using those values, you would obtain 10 ATP for
each acetyl-CoA oxidized.

140. So, for an even-numbered saturated fat (C2n) ("C" indicating
the number of carbon atoms and noted 2n is in the subscript), n
- 1 oxidations are required, and the final process yields an 1
more acetyl CoA i.e. for palmitate if 2n=16 then n=8, which
required n-1 oxiation i.e 7, so there will be 7 FAD, 7 NADH and
8 acetyl COA which will produce 1.5 ATP, 2.5 ATP and 10 ATP
respectively and cumulatively it will be calculated 108 where 2
ATP were used in the initial activation of fatty acid so 2 ATP will
be subtracted and total number of ATP will become 106. But if
you go with the thereotical yields and have larger production
ATP source then values of NADH, FAD and ATP produced by
the full rotation of citric acid cycle will produce 3, 2, 12 ATPs.
Together ATP number will become 131 and 2 will be subtracted
as required for initial activation of fatty acid so you will remain
with 129 !!!!!!!!!

141. An 18C stearic fatty acid will create:
9 acetyl CoA, which form 90 ATP
8 FADH2 which form 12 ATP
& 8 NADH which form 20 ATP
Total = 122 ATP (-2 ATP for F.A. activation)
=120 ATP!
ATP production from
Fatty Acid Oxidation

142. Well first - What is NADH? It's an electron carrier. NADH
releases its 2 electrons into the Electron Transport Chain.
These 2 electrons pass through all 5 electron carriers.
Everytime an electron passes through an electron carrier, 1
Proton is pumped from the Matrix to the intermembrane space.
Because there are 2 electrons and they are passed in total 5
times, 10 Protons are pumped through per NADH.
To phosphorylate ADP + Pi -> ATP requires the pumping of 3
Protons. However, 1 Proton is needed to transport Cytosolic Pi
into the Mitrochondrial Matrix. Therefore, 4 Protons are "used
up" per ATP molecule created.
Since each NADH yields 10 Protons - 5 ATP molecules are
created per 2 NADH (or 2.5 ATP per).

144. FADH2 doesn't release its electrons to the first
carrier of the ETC (NADH Dehydrogenase).
Instead it releases its electrons to the ETC carrier,
Ubiquione. As a result, it yields a total of 6 Protons
per FADH and ultimately results in the creation of
3 ATP molecules per 2 FADH or (1.5 ATP per).

146. To pass the electrons from NADH to last Oxygen
acceptor, a total of 10 protons are transported
from matrix to inter mitochondrial membrane. 4
protons via complex 1,4 via complex 3 and 2 via
complex 4. And to make 1 ATP ,4 protons move
from inter mitochondrial membrane to matrix via
ATPase. Thus for NADH— 10/4=2.5 ATP is
produced actually.
Similarly for 1 FADH2, 6 protons are moved so
6/4= 1.5 ATP is produced.

147. An 18C stearic fatty acid will create = 120 ATP
1 Glucose will = 32 ATP
1 Stearic acid will = 120 ATP
3x 6C Glucose = 18 Carbons
32 ATP x 3 =96 ATP
Lipids are 25% more efficient at energy storage!

148. Example: Energy of palmitoyl ~Co
A (16 C) oxidation
• Number of cycles= n/2 -1 = 7 cycles
• Number of acetyl ~Co A = n/2 =8
 So, 7 NADH, each provide 3 ATP when oxidized in the
ETC 7X3=21 ATP
 7 FADH2 each provide 2 ATP when oxidized in the ETC
7x 2=14 ATP
 8 acetyl ~Co A , each provides 12 ATP when converted to
CO2& H2O by the TCA cycle 8x12= 96 ATP
So total energy yield of oxidation of palmitoyl ~Co A = 21 +
14 + 96 = 131 ATP
• As 2 molecules of ATP are used in the activation of a
molecule of fatty acid Therefore, there is a net yield of
129 molecules of ATP

149. Palmitic Acid -ATP Synthesis
• Palmitic Acid is C-16
• Initiating Step - requires 1 ATP (text says 2)
• Step 1 - FAD into e.t.c. = 2 ATP
• Step 3 - NAD+ into e.t.c. = 3 ATP
• Total ATP per turn of spiral = 5 ATP
Example with Palmitic Acid = 16 carbons = 8 acetyl
groups
• Number of turns of fatty acid spiral = 8-1 = 7 turns
• ATP from fatty acid spiral = 7 turns and 5 per turn = 35
ATP.
• NET ATP from Fatty Acid Spiral = 35 - 1 = 34 ATP

150. Palmitic Acid (C-16) -ATP Synthesis
ATP Synthesis form Acetyl Coa Through Citric Acid
Cycle
In Citric Acid Cycle
1 GTP = 1 ATP
3 NADH = 3 x 3 = 9 ATP
1 FADH = 2 x 1 = 2 ATP
Total ATP per Acetyl Coa in TCA cycle = 12
• 8 Acetyl CoA = 8 turns C.A.C.
• 8 turns x 12 ATP/C.A.C.= 96 ATP
• GRAND TOTAL = 35 – 1 + 96 = 130 ATP

151. In terms of energy from food:
Fatty acids yield > 2x the energy per gram.
1 gram of carbohydrates = 4 kcal (food calories)
1 gram of fat = 9 kcal of energy
Which fuel is the most commonly used?
Skeletal muscles at rest use fatty acids;
Active skeletal muscles use glucose
Cardiac muscles: 1st fatty acids,
then Ketone bodies, glucose, & lactate.
Liver prefers to use fatty acids
Brain only uses glucose & ketone bodies

152. “fats burn in the flame of
carbohydrates” Or why does an untreated diabetics
breath smell “fruity”
• Acetyl CoA from fatty acid oxidation enters Kreb’s cycle only if fat and
carbohydrate degradation are balanced.
– To enter Kreb’s cycle, Acetyl CoA from fatty acid oxidation must combine with
oxaloacetate.
• [oxaloacetate] is dependent on presence of carbohydrate oxidation.
• During fasting (or diabetes) oxaloacetate is “bleed off” and converted to pyruvate to
synthesize glucose in gluconeogenesis. During gluconeogenesis the rate of Kreb’s
Cycle slows.
• REMEMBER: humans lack the ability to synthesize glucose from Acetyl
CoA.

153. The Body
• Fat cell
– Storage of
triacylglycerol
– Release of fatty
acids / glycerol
• Mt of Liver cell
– β oxidation of fatty
acids
– Synthesis of Ketone
bodies
• Ketone bodies are
normal energy source
for certain tissue
– Acetoacetate for
• heart muscle
• Renal cortex
• High levels of ketone
bodies is life
threatening because
ketone bodies are
moderately strong
acids leading to
acidosis.
– Decrease in pH
impairs tissue
function.

154. Differences in the oxidation
and synthesis of FAs

155. Differences between Fatty Acid
Synthesis and Degradation
• Synthesis
– 1. Cytoplasm
– 2. Intermediates linked to
sulfhydryl of acyl carrier
protein (ACP)
– 3. Synthetic enzymes are
associated into fatty acid
synthase
– 4. Synthesized by sequential
addition of Acetyl CoA from
activated donor (malonyl
ACP)
– 5. Reductant = NADPH
– 6. Basic synthesis stops at
palmitate (C16)
• Oxidation
– 1. Mt matrix
– 2 Intermediates linked to
sulfyhdryl of CoA.
– 3. Oxidative enzymes are NOT
associated.
– 4. Fatty acids oxidized into
Acetyl CoA
– 5. Oxidant = NAD+ and FAD
– 6. we just looked at this for
degradation.