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Chapter 24A
Nutrition, Metabolism,
Body Temperature
Slides by Barbara Heard and W. Rose.
figures from Marieb & Hoehn 9th ed.
Portions copyright Pearson Education
Nutrition
• Most ingested nutrients used for metabolic
fuel
• Some for cell structures and molecular
synthesis
• Energy value measured in kilocalories
(kcal)
– Heat needed to raise temperature of 1 kg H2O
by 1C
• What happens to absorbed nutrients?
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Nutrition
• Nutrient - substance in food for growth,
maintenance, repair
• Major nutrients – bulk of ingested food
– Carbohydrates, lipids, and proteins
• Other nutrients – required in small
amounts
– Vitamins and minerals
• Water required so technically a nutrient
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Nutrition
• Food groups
– Fruits
– Vegetables
– Grains
– Protein
– Dairy
• Eat less overall; plenty of fruits,
vegetables, whole grains; avoid junk food;
exercise
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Nutrition
• Liver can convert many molecules into
those needed
• Essential nutrients
– Diet must provide; liver cannot synthesize
– Possibly 50 molecules
• Non-essential nutrients vital to life as well
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Carbohydrates
• Dietary sources – primarily from plants
– Starch (complex carbohydrates) in grains and
vegetables
– Sugars (mono- and disaccharides) in fruits,
sugarcane, sugar beets, honey and milk
– Fiber: not a source of calories cuz we can’t
digest - cellulose in vegetables; provides
roughage
• ~4 kcal / g
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Carbohydrates: Uses in Body
• Glucose - fuel used by cells to make ATP
– Some cells use fats for energy
• Neurons and RBCs ~ entirely on glucose; neurons
die quickly without glucose
• Excess glucose converted to glycogen or
fat and stored
• Fructose and galactose converted to
glucose by liver
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Carbohydrates
Dietary recommendations
• Recommended intake - 45–65% of total calorie
intake; mostly complex carbohydrates
– Whole grains and vegetables
• At least 130 g/day (male & female)
Source: 2010 Dietary Guidelines for Americans
http://www.health.gov/dietaryguidelines/dga2010/dietaryguidelines2010.pdf
Lipids
• Dietary sources
– Triglycerides (neutral fats)
• Saturated fats in meat, dairy foods, and tropical
oils; hydrogenated oils (trans fats)
• Unsaturated fats in seeds, nuts, olive oil, and most
vegetable oils
– Cholesterol in egg yolk, meats, organ meats,
shellfish, and milk products
• Liver makes ~85% cholesterol despite intake
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Triglyceride
Cholesterol
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Testosterone
Estradiol
Lipids
• Liver can interconvert many fatty acids
• Essential fatty acids
– Linoleic acid
– Linolenic acid
Found in most vegetable oils
Linolenic 18C
Linoleic 18C
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Lipids: Uses in Body
• Help absorb fat-soluble vitamins
• Major fuel of hepatocytes and skeletal muscle
• Phospholipids essential in myelin sheaths and
all cell membranes
• Adipose tissue  protection, insulation, fuel
storage
• Cholesterol stabilizes membranes; precursor of
bile salts, steroid hormones
• ~9 kcal / gram
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Lipids
• Dietary guidelines*
– Fats: 20-35% of total caloric intake
– Saturated fats: <10% of calories (0% is OK)
– Cholesterol: < 300 mg/day (0 mg is OK)
• Goal
– Keep cholesterol < 200 mg/dl
• Typical American diet : Fats provide
approx. 35% of calories*
* 2010 Dietary Guidelines for Americans.
No minimum lipid intake determined
by Food & Nutrition Board, Inst. Of Med., 2002/2005.
Proteins
• Dietary sources
– Eggs, milk, fish, most meats, soybeans
contain complete proteins
• Contain all needed amino acids
– Legumes, nuts, and cereals contain
incomplete proteins (lack some essential
amino acids)
– Legumes and cereal grains together contain
all essential amino acids
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Proteins: Uses in Body
• Structural materials
– Keratin (skin); collagen and elastin
(connective tissue); muscle proteins
• Functional molecules
– Enzymes, some hormones
• Amino acids can be burned for energy
• ~4 kcal / gram
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Proteins: Use of Amino Acids
• All-or-none rule
– All amino acids needed must be present for
protein synthesis to occur; if not all present
amino acids used for energy
• Adequacy of caloric intake
– Protein used as fuel if insufficient
carbohydrate or fat available
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Proteins: Use of Amino Acids
• Nitrogen balance
– Rate of protein synthesis equals rate of
breakdown and loss
– Positive nitrogen balance - synthesis exceeds
breakdown (normal in children, pregnant
women, tissue repair)
– Negative nitrogen balance - breakdown
exceeds synthesis (e.g., stress, burns,
infection, injury, poor dietary proteins,
starvation)
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Figure 24.2 Essential amino acids.
Tryptophan
Methionine
(Cysteine)
Tryptophan
Valine
Methionine
Threonine
Total
protein
needs
Valine
Phenylalanine
(Tyrosine)
Threonine
Leucine
Phenylalanine
Isoleucine
Leucine
Lysine
Histidine
(Infants)
Beans
and other
legumes
Corn and
other grains
Isoleucine
Lysine
Arginine (Infa
nts)
Essential amino acids
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Vegetarian diets providing the eight essential
amino acids for humans
Proteins
• Dietary requirements
– Needs reflect age, size, metabolic rate,
nitrogen balance
– 0.66 gram per kg body weight per day*
– i.e. approx. 1.5 ounce protein/day for 155 lb
person
– American diet provides more than needed
*Dietary Reference Intakes, Food & Nutrition Board,
Institute Of Medicine (USA), 2002/2005, for adults.
Recommended daily protein intake per kg is higher for
children & pregnant & lactating women.
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Vitamins
•
•
•
•
Organic compounds
Crucial in helping body use nutrients
Most function as coenzymes
Vitamins D (skin), some B and K
synthesized by intestinal bacteria; betacarotene (carrots) converted in body 
vitamin A
• Rest must be ingested
• No one food group contains all vitamins
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Vitamins
• Water-soluble, fat-soluble
• Water-soluble vitamins
– B complex and C are absorbed with water
– B12 absorption requires intrinsic factor
– Not stored in the body
• Any not used within an hour or so is excreted
• Therefore megadoses offer little or no value
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Vitamins
• Fat-soluble vitamins
– A, D, E, and K absorbed with lipid digestion
products
– Stored in body, except for vitamin K
• Pathologies due to excess
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Vitamins
• Free radicals generated during normal
metabolism
– Vitamins C, E, A, and mineral selenium 
antioxidants
• Neutralize free radicals
• Broccoli, cauliflower, brussels sprouts good
sources of vitamins A and C
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Minerals
• Seven required in moderate* amounts
– Calcium, phosphorus, potassium, sodium,
chlorine, magnesium, sulfur
• Others required in trace amounts
– Fe, Zn top the list at 8-18 mg/day
• Work with nutrients to ensure proper body
functioning
• Uptake and excretion balanced to prevent
toxic overload
* 0.3 to 4 g/day in adults. No DRI for S since adequate
protein intake will yield enough. See DRI Tables, Food &
Nutrition Board, IOM, 1997-2011.
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Minerals
• Examples
– Calcium, phosphorus, and magnesium salts
harden bone
– Iron essential for oxygen binding to
hemoglobin
– Iodine necessary for thyroid hormone
synthesis
– Sodium and chloride major electrolytes in
blood
• Mineral-rich foods
– Vegetables, legumes, milk, some meats
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Metabolism
• Metabolism - biochemical reactions inside
cells involving nutrients
• Two types of reactions
– Anabolism - synthesis of large molecules
from small ones
• Ex. Amino acids  proteins
– Catabolism - hydrolysis of complex structures
to simpler ones
• Ex. Proteins  amino acids
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Metabolism
• Cellular respiration
– Catabolism of food fuels  capture of energy
to form ATP in cells
• Enzymes shift high-energy phosphate
groups of ATP to other molecules
(phosphorylation)
• Phosphorylated molecules activated to
perform cellular functions
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Stages of Metabolism
• Three stages in processing nutrients
– Digestion, absorption, and transport to tissues
– Cellular processing (in cytoplasm)
• Synthesis of lipids, proteins, and glycogen, or
• Catabolism (glycolysis) into pyruvic acid and
acetyl CoA
– Oxidative (mitochondrial) breakdown of
intermediates into CO2, water, and ATP
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Cellular Respiration
• Goal  trap chemical energy in ATP
– Energy also stored in glycogen and fats
– Oxidation of food for fuel
• Step by step removal of pairs of hydrogen atoms
(and electron pairs) from substrates  only CO2
left
• Includes glycolysis, Krebs cycle,
oxidative phosphorylation
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Figure 24.3 Three stages of metabolism of energy-containing nutrients.
Stage 1 Digestion in GI tract
lumen to absorbable forms.
PROTEINS
Transport via blood to
tissue cells.
CARBOHYDRATES
FATS
Glucose and
other sugars
Glycerol Fatty acids
Amino acids
Stage 2 Anabolism
(incorporation into
molecules) and
catabolism of nutrients to
form intermediates within
tissue cells.
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Glycogen
Pyruvic acid
Infrequent
Stage 3 Oxidative breakdown
of stage 2 products occurs in
mitochondria of tissue cells. CO2
is liberated, and H atoms removed are
ultimately delivered to molecular oxygen,
forming water. Some energy released is
used to form ATP.
Catabolic reactions
Anabolic reactions
Glycolysis
Glucose
Proteins
Acetyl CoA
Krebs
cycle
Oxidative
phosphorylation
(in electron
transport chain)
Fats
ATP Synthesis
• Two mechanisms
– Substrate-level phosphorylation
• A small contribution, in cytoplasm
– Oxidative phosphorylation
• The majority of ATP made this way; in
mitochondria
• Chemiosmotic process
• ATP synthase
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Mechanisms of phosphorylation: Oxidative phosphorylation
High H+ concentration in
intermembrane space
Membrane
Proton
pumps
(electron
transport
chain)
ATP
synthase
Energy
from food
Low H+ concentration
in mitochondrial matrix
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Carbohydrate Metabolism
Glucose enters cell by facilitated diffusion
Complete glucose catabolism requires three
pathways
• Glycolysis (cytoplasm)
• Krebs cycle (mitochondrial matrix)
• Electron transport chain and oxidative
phosphorylation (mitochodrial inner membrane)
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ATP formation by cellular respiration, in cytosol and mitochondria.
Chemical energy (high-energy electrons)
Chemical energy
Glycolysis
Glucose
Cytosol
Electron transport
chain and oxidative
phosphorylation
Krebs
cycle
Pyruvic
acid
Inner
mitochondrial
membrane (cristae)
Mitochondrion
Via oxidative
phosphorylation
Via substrate-level
phosphorylation
1 Glycolysis, in the cytosol,
breaks down each glucose
molecule into two molecules of
pyruvic acid.
2 The pyruvic acid then enters
the mitochondrial matrix, where
the Krebs cycle decomposes it to
CO2. During glycolysis and the
Krebs cycle, substrate-level
phosphorylation forms small
amounts of ATP.
3 Energy-rich electrons picked up
by coenzymes are transferred to the
electron transport chain, built into
the cristae membrane. The electron
transport chain carries out oxidative
phosphorylation, which accounts
for most of the ATP generated by
cellular respiration.
Carbohydrate Metabolism
Net result of complete oxidation of glucose
(aerobic: with O2)
C6H12O6 + 6O2
6H2O + 6CO2 + ~30 ATP + heat
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Carbohydrate Metabolism
Glycolysis: Initial stage of glucose breakdown
• Occurs in cytoplasm
• Does not require oxygen
1 glucose + 2 ADP +2 Pi + 2 NAD+
2 pyruvate + 2 ATP + 2 NADH
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Carbohydrate Metabolism
Glycolysis requires NAD+ to work
After glycolysis (2 pyruvate + 2 ATP + 2
NADH):
• If there’s O2:
– Pyruvates enter TCA cycle
– NADH gets oxidized with the help of the electron
transport chain (oxidative phosphorylation)
• If there’s NOT O2:
– NADH reacts with pyruvate to make NAD+ and lactic acid
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Glycolysis
• Fate of lactic acid:
– Some leaves cell and goes to liver
• May be converted to glucose-6-phosphate (G6P)
• G6P stored as glycogen or de-phosphorylated to
make glucose
• Prolonged anaerobic metabolism causes
acid build-up: lactic acidosis
• Glycolysis: makes ATP faster than aerobic
respiration; yields much less ATP
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Krebs Cycle
• Occurs in mitochondrial matrix
• Fueled by pyruvic acid and fatty acids
• Transitional phase converts each pyruvic
acid to acetyl CoA in three steps
• Decarboxylation - removal of 1 C to produce acetic
acid and CO2
• Oxidation – H atoms removed from acetic acid; picked
up by NAD+  NADH + H+
• Forms acetyl CoA: Acetic acid + coenzyme A  acetyl
coenzyme A (acetyl CoA)
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Krebs Cycle
• Products of each turn of Krebs cycle
– 3 NADH + H+, 1 FADH2, 2 CO2, 1 ATP
• 1 glucose  2 pyruvic acid molecules 
two turns of Krebs cycle  final products
– 6 NADH + H+, 2 FADH2, 4 CO2, 2 ATP
• Adding products of transitional phase, final
products
– 8 NADH + H+, 2 FADH2, 6 CO2, 2 ATP
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Krebs Cycle
• Does not directly use O2
– NADH molecules must be oxidized in electron
transport chain for Krebs cycle to continue
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Electron Transport Chain and Oxidative
Phosphorylation
• Directly uses oxygen
• Overview
– NADH + H+ and FADH2 (from glycolysis and
Krebs cycle) deliver hydrogen atoms
– Hydrogen atoms combined with O2  water
– Released energy harnessed  ATP by
oxidative phosphorylation
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Electron Transport Chain and Oxidative
Phosphorylation
• Involves chain of proteins bound to metal
atoms (cofactors) on inner mitochondrial
membrane
– Some – flavins - derived from riboflavin
– Most – cytochromes – iron-containing
pigments
– Neighboring carriers form four respiratory
enzyme complexes
• Alternately reduced and oxidized as pick up and
pass electrons
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Electron Transport Chain and Oxidative
Phosphorylation
• Pumped H+ creates electrochemical
proton gradient
– Created pH gradient; voltage across
membrane
– H+ attracted to matrix side of membrane by
pH gradient and voltage
– H+ diffuses back to matrix via ATP synthase
 electrical current
– ATP synthase uses electrical current  ATP
PLAY
Animation: Electron Transport
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Electron Transport Chain and Oxidative
Phosphorylation
• Transfer of energy from NADH + H+ and
FADH2 to oxygen releases large amounts
of energy
• Energy released in controlled steps
through electron transport chain
• Electron pairs + oxygen atom  O–
– O– attracts H+  water
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Figure 24.8 Oxidative phosphorylation has two phases.
Glycolysis
Outer mitochondrial
membrane
Phase 1:
Electron transport creates the
proton gradient.
Phase 2:
Chemiosmosis uses
the proton gradient
to synthesize ATP.
Intermembrane
space
Inner
mitochondrial
membrane
(crista)
III
I
Electron transport
Krebs chain and oxidative
cycle
phosphorylation
IV
II
ATP
V
synthase
1 Reduced coenzymes
(NADH + H+ and FADH2)
deliver electrons picked
up during the oxidation
of food fuels to
respiratory enzyme
complexes I and II.
Mitochondrial
matrix
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2 The electrons are transferred from
one complex to another in the
membrane. Each complex is reduced
and then oxidized, releasing energy
that is used to pump H+ into the
intermembrane space. This creates an
electrochemical gradient between the
matrix and the intermembrane space.
Coenzyme Q (ubiquinone) and cytochrome c are mobile carriers that
shuttle between the larger complexes.
3 At respiratory
enzyme complex IV,
electron pairs
combine with two
protons (H+) and a
half molecule of O2,
forming water.
4 Complex V,
called ATP synthase,
harnesses energy of the
proton gradient to
synthesize ATP. As H+
flows back across the
membrane through ATP
synthase, the synthase
rotor spins, causing Pi to
attach to ADP, forming ATP.
Structure and
function of
ATP synthase
Intermembrane space
A rotor in the
membrane spins
clockwise when H+
flows through it
down the H+
gradient.
A stator anchored in
the membrane holds
the knob stationary.
As the rotor spins,
a rod connecting
the cylindrical rotor
and knob also
spins.
Mitochondrial matrix
The protruding,
stationary knob
contains three
catalytic sites that
join inorganic
phosphate to ADP
to make ATP when
the rod is spinning.
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ATP synthase animation. Shows H+ going from intermembrane space below to matrix above.
Source: www.bioc.aecom.yu.edu/labs/girvlab/ATPase/ATPsynthase.mov.
KAAP
ATP synthase animation. Makes 3 ATP / rev.
Inytermembrane space below, matrix above. ATP=pink,
ADP=green, Pi=blue. H+ not shown. Source: MRC (UK).
KAAP
Summary of ATP Production
• Energy use at rest averages 100 kcal/hour
= 116 watts
– Huge demand on mitochondria
• 1 mole glucose = 686 kcal; 262 kcal
captured in ATP (rest lost as heat)
– 38% efficiency
– Man-made machines ~ 10–30% efficiency
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Summary of ATP Production
• Complete oxidation of 1 glucose molecule
• Glycolysis + Krebs cycle + electron
transport chain  CO2 + H2O  32
molecules ATP
– By both substrate-level and oxidative
phosphorylation
• But, energy required to move NADH + H+
generated in glycolysis into mitochondria
 final total ~ 30 molecules ATP
– Total not exact, partly due to unclear
stoichiometry of ATP synthase
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Energy yield during cellular respiration
Mitochondrion
Cytosol
Electron
shuttle across
mitochondrial
membrane
Glycolysis
Glucose
Pyruvic
acid
2
Acetyl
CoA
Krebs
cycle
Electron transport
chain and oxidative
phosphorylation
(4 ATP – 2 ATP
used for
activation
energy)
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Typical
ATP yield
per glucose
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by oxidative
phosphorylation
Glycogenesis and Glycogenolysis
• Glycogenesis
– Glycogen formation via glycogen synthase
when glucose supplies exceed need for ATP
synthesis
– Mostly in liver and skeletal muscle
• Glycogenolysis
– Glycogen breakdown via glycogen
phosphorylase in response to low blood
glucose
– Only by hepatocytes, some kidney and
intestinal cells
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Glycogenesis
and
glycogenolysis
Blood glucose
Cell exterior
Hexokinase
(all tissue cells)
Glucose-6phosphatase
(present in liver,
kidney, and
intestinal cells)
Glucose-6-phosphate
Glycogenolysis
Glycogenesis
Mutase
Mutase
Glucose-1-phosphate
Pyrophosphorylase
Glycogen
phosphorylase
Uridine diphosphate
glucose
Cell interior
Glycogen
synthase
Glycogen
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Athletes and Carbohydrates
• Complex carbohydrates  more glycogen
storage in muscle; more effective than
high-protein meal for intense muscle
activity
• Carbo loading
– Carbohydrate-rich diet for 3-4 days;
decreased activity  muscles store more
glycogen
–  improved performance and endurance
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Gluconeogenesis
• Glucose formed in liver from glycerol and
amino acids when blood glucose levels
drop
• Protects against damaging effects of
hypoglycemia
– Especially important for nervous system
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Lipid Metabolism
• Greater energy yield than from glucose or
protein catabolism
– Fat catabolism yields 9 kcal per gram versus
4 kcal per gram of carbohydrate or protein
• Most products of fat digestion transported
in lymph as chylomicrons
• Hydrolyzed by endothelial enzymes into
fatty acids and glycerol
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Lipid Metabolism
• Only triglycerides routinely oxidized for
energy
• Two building blocks oxidized separately
– Glycerol pathway
– Fatty acid pathway
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Lipid Metabolism: Glycerol
• Glycerol  glyceraldehyde 3-phosphate
(same as in glycolysis)
– Enters Krebs cycle
– ATP yield ~½ that of glucose  15
ATP/glycerol
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Lipid Metabolism: Fatty Acids
• Fatty acids undergo beta oxidation in
mitochondria 
– Fatty acid chains broken  two-carbon acetic
acid fragments and reduced coenzymes
• Acetic acid  acetyl CoA  Krebs cycle
• Reduced coenzymes  electron transport chain
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Lipogenesis
• Dietary glycerol and fatty acids not needed
for energy  stored triglycerides
• Triglyceride synthesis (lipogenesis) occurs
when cellular ATP and glucose levels high
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Lipolysis
• Reverse of lipogenesis
– Stored fat  glycerol and fatty acids for fuel
• Preferred by liver, cardiac muscle, resting skeletal
muscle
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Synthesis of Structural Materials
• Phospholipids for cell membranes and
myelin
• Cholesterol for cell membranes and
steroid hormone synthesis
• In liver
– Synthesis of transport lipoproteins for
cholesterol and fats
– Synthesis of cholesterol from acetyl CoA
– Use of cholesterol to form bile salts
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