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Chapter 5
Cell Respiration & Metabolism
5-1
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Chapter 5 Outline
Glycolysis
Aerobic
Respiration
Fat & Protein Metabolism
5-2
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Metabolism
Is
all reactions in body that involve energy
transformations
Divided into 2 categories:
Catabolism breaks down molecules & releases
energy
Is primary source of energy for making ATP
Anabolism makes larger molecules & requires
energy
Source of body’s large energy-storage
compounds
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Glycolysis
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Glycolysis
Is
metabolic pathway by which glucose is converted to
2 pyruvates
Does not require oxygen
Overall net equation is:
glucose + 2NAD + 2ADP + 2Pi  2 pyruvates +
2NADH + 2 ATP
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Glycolysis continued
 Glycolysis
is exergonic - produces net of 2ATPs & 2NADHs
 However, glucose must be activated with 2ATPs
(phosphorylation) before energy can be obtained
 Phosphorylation traps glucose inside cell
 Below can see 2ATPs added & 4 are produced for a net gain of
2 ATP
Fig 5.1
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Glycolysis continued
Fig 5.2
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Lactic Acid Pathway
To
avoid end-product inhibition, NADHs produced in
glycolysis need to give Hs away
In absence of O2, NADH gives its Hs to pyruvate
creating lactic acid (anaerobic respiration)
Makes muscles feel fatigued
Fig 5.3
5-8
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Lactic Acid Pathway continued
RCCs
don't have mitochondria; use only lactic acid
pathway
Occurs in skeletal & heart muscle when oxygen supply
falls below critical level
During heavy exercise or vascular blockage
5-9
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Glycogenesis & Glycogenolysis
For
osmotic reasons cells can't store many free
glucoses
Instead store glucose as glycogen (glycogenesis)
Skeletal muscle & liver store lots of glycogen
Glycogenolysis clips glucose out of glycogen as
glucose 6-phosphate
Phosphate groups trap molecules in cells
5-10
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Glycogenesis & Glycogenolysis continued
 Skeletal
muscles use
trapped glucose-6phosphate for own
energy needs
 Only liver has glucose-6phosphatase that
removes phosphate
groups
 So glucose can be
secreted
Fig 5.4
5-11
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Cori Cycle
 Some
skeletal muscle lactic acid goes to liver
 Where it is converted back through pyruvate to glucose &
glycogen
 Called gluconeogenesis
 Also can happen with amino acids & glycerol
Fig 5.5
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Aerobic Respiration
5-13
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Aerobic Respiration
 Begins
when pyruvate formed by glycolysis enters mitochondria
 C02 is clipped off pyruvate forming acetyl CoA (coenzyme A
is a carrier for acetic acid)
 C02 goes to lungs
 Energy in acetyl CoA is extracted during aerobic
respiration in mitochondria
Fig 5.6
5-14
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Krebs Cycle
Fig 5.7
 Begins
with acetyl
CoA combining with
oxaloacetic acid to
form citric acid
 In a series of
reactions citric acid
converted back to
oxaloacetic acid to
complete the
pathway
5-15
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Krebs Cycle continued
 Produces
1 GTP, 3 NADH, & 1 FADH2
 NADH & FADH2 carry electrons to Electron Transport Chain
(ETC)
5-16
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Krebs Cycle continued
Fig 5.8
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Electron Transport & Oxidative
Phosphorylation
 The
electron transport chain is a linked series of proteins on the
cristae of mitochondria
 Proteins are FMN, coenzyme Q, & cytochromes
Fig 3.10
5-18
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Electron Transport & Oxidative
Phosphorylation continued
NADH
& FADH2 from Krebs carry electrons to ETC
Which are then shuttled in sequence through ETC
NAD & FAD are regenerated to shuttle more
electrons from Krebs Cycle to ETC
5-19
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Electron Transport & Oxidative
Phosphorylation continued
 As
each protein in ETC
accepts electrons it is
reduced
 When it gives
electrons to next
protein it is oxidized
 This process is
exergonic
 Energy is used to
phosphorylate ADP
to make ATP
 Called oxidative
phosphorylation
Fig 5.9
5-20
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Chemiosmotic theory
 Energy
gathered by ETC
is used to pump H+s into
mitochondria outer
chamber
 Creating high H+
concentration there
 As H+s diffuse down
concentration & charge
gradient thru ATP
synthase, & back into
inner chamber, their
energy drives ATP
synthesis
(Chemiosmotic theory)
Fig 5.10
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Function of Oxygen
Fig 5.10
 Electrons
added to
beginning of ETC are
passed along until reach
end
 Have to be given
away or would stop
ETC
 O2 accepts these
electrons & combines
with 4H+s
 O2 + 4 e- + 4 H+  2 H20
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ATP Formation
ATP
can be made 2 ways:
Direct (substrate-level) phosphorylation
Where ATP is generated when bonds break
Both ATPs in glycolysis made this way
2 ATPs/glucose in Kreb's made this way
Oxidative phosphorylation in Kreb's
Where ATP generated by ETC
30-32 ATPs made this way
5-23
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ATP Formation continued
3H+s
pass thru ATP synthase to generate 1 ATP
This yields 36-38 ATPs/glucose
However some of these are used to pump ATPs
out of mitochondria
So net yield is 30-32 ATPs/glucose
Really takes 4H+s to generate 1 exported ATP
5-24
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Production of ATP by ETC
2.5 ATP
produced for each pair of electrons NADH
donates
1.5 ATP produced for each pair of electrons FADH2
donates
Net of 26 ATP produced in ETC
5-25
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Net Production of ATP
26 ATP
produced in ETC
2 from glycolysis
2 from direct phosphorylation in Kreb’s
For total of 30 ATPs for each glucose
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5-27
Fat & Protein Metabolism
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Fats & Proteins as Energy Sources
Fats
can be hydrolyzed to glycerol & fatty acids
These can be modified to run thru Kreb's
Proteins can be broken down to amino acids
Which can be deaminated & run thru Kreb's
These pathways can be used to interconvert
carbohydrates, fats, & proteins
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Energy Storage
When
more
energy is taken in
than consumed,
ATP synthesis is
inhibited
Glucose
converted into
glycogen & fat
Fig 5.11
5-30
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Acetyl CoA
Is
a common substrate for energy & synthetic
pathways
Fig 5.12
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Fat Synthesis (Lipogenesis)
Acetyl
CoAs can be linked together to form fatty acids
Fatty acids + glycerol = Fat (triglycerides)
Occurs mainly in adipose & liver tissues
Fat is major form of energy storage in body
Yields 9 kilocalories/g
Carbs & proteins yield only 4/g
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Lipolysis
Is
breakdown of fat into fatty acids & glycerol
Via hydrolysis by lipase
Acetyl CoAs from free fatty acids serve as major
energy source for many tissues
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Acetyl CoA from Fat --Beta-Oxidation
Beta-oxidation
clips acetyl CoAs
off fatty acid
chains
Which can be
run thru Kreb's
giving 10ATPs
each
Plus oxidation itself
yields 4 ATPs
Fig 5.13
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Brown Fat
Amount
of brown fat greatest at time of birth
Major site for thermogenesis in the newborn
Brown fat produces uncoupling protein, causing H+ to
leak out of inner mitochondrial membrane
Less ATP produced, causes electron transport
system to be more active
Heat produced instead of ATP
5-35
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Ketone Bodies
Triglycerides
are continually broken down &
resynthesized
Ensures blood will contain fatty acids for aerobic
respiration
During fasting & diabetes lots of fat is broken down
Causes high levels of ketone bodies
Fat metabolites
Gives breath an acetone smell
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Amino Acid Metabolism
Nitrogen
(N) ingested primarily as protein
Which is used in body as amino acids
Excess is excreted mainly as urea
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Nitrogen (N) Balance
Nitrogen
balance = N ingested minus N excreted
Positive N balance: more N ingested than excreted
Negative N balance: less N ingested than excreted
In healthy adults amount of N excreted = amount
ingested
Excess amino acids can be converted into carbos & fat
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Essential & Non-essential Amino Acids
 20
amino acids used to build proteins
 12 can be produced by body
 8 must come from diet (= essential amino acids)
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Transamination
New
amino acids can be obtained by transamination
Which is addition of -NH2 to pyruvate or Kreb's cycle
ketones to make a new amino acid
Catalyzed by transaminase
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Fig 5.14
Transamination continued
5-41
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Oxidative Deamination
Is
process by which excess amino acids are eliminated
-NH2 is removed from glutamic acid, forming keto acid
& ammonia
Ammonia is converted to urea & excreted
Keto acid goes to Kreb’s or to fat or glucose
Fig 5.15
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Gluconeogenesis
Occurs
when amino acids are converted to Keto acids,
then pyruvate, then glucose
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Uses of Different Energy Sources
Different
cells have different preferred energy
substrates
Brain uses glucose as its major source of energy
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