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Cellular Respiration – Chapter 8
I. Cellular Respiration Basics
A. Importance
1. Breakdown of high energy
molecules to release energy
2. All living organisms require
energy to maintain life
processes
3. aerobic respiration = requires
oxygen
4. anaerobic respiration = does
not require oxygen (yeast,
bacteria)
5. some organisms produce their
own “high energy” food
molecules (autotrophic –
“producers – plants, some
bacteria) while other obtain
their food molecules from other
sources (heterotrophic –
animals, fungi)
B. Coenzymes – smaller, non
protein organic molecules that
act as “shuttle” molecules
carrying substances from one
enzyme catalyzed reaction to
another
1. some carry electrons (FAD,
NAD+, FMN, coenzyme Q)
2. ATP carries phosphate groups
3. H carrying coenzymes (NAD+)
II. Chemical Reactions of Cellular
Respiration
A. Overall reaction
C6H12O6 + O2  CO2 + H2O + Energy (ATP)
1. four sets of reactions
2. occurs in the cytoplasm and
mitochondria (cristae – inner
membrane)
3. oxidation/reduction reaction
(LEO goes GER!!!)
4. exergonic – energy releasing
(products are at a lower energy
than the reactants)
B. Glycolysis (breakdown of glucose
into 2 pyruvate molecules =
C3H4O3)
1. occurs in the cytoplasm
2. does not require oxygen
3. occurs in 8 different reactions
4. net production of 2 pyruvates, 2
molecules of ATP, 2NADH)
5. input of glucose and 2 ATP and 2
NAD+)
C. Transition (preparation for the
citric acid cycle) reaction
1. pyruvate is changed into acetyl
CoA, releasing CO2
2. Coenzyme A, pyruvate, and
NAD+ enter the reaction
3. Acetyl CoA (coenzyme A) =
C2H3O + CO2 + NADH leave
the reaction
D. Kreb’s cycle or Citric Acid cycle
1. a series of enzyme mediated
reactions linked to each other in
which several carbon chain
intermediates are produces (C6,
C5, C4)
2. First intermediate formed is
Citrate (Citric acid cycle)
3. Acetyl Co-A enters the cycle and
bonds with oxaloacetate (C4) 
C6
4. 9 separate reactions
5. cycle occurs twice for each
glucose metabolized
6. each cycle produces 2 CO2
molecules and 2 ATP (substrate
level phosphorylation – enzyme
controlled)
7. each cycle releases 3 NADH + H
and 1 FADH2
8. occurs in the mitochondrial
matrix
E. Electron transport and
chemiosmotic ATP synthesis
1. occurs in the cristae membrane
2. NADH and FADH2 shuttle their
H atoms and release them at the
membrane
3. H+ are pushed through the
membrane into the space between
the outer and inner membrane
(H+ reservoir)
4. e- move from one carrier to
another in the cristae membrane
5. final e- pair acceptor is O2
6. when the proper pH is reached,
the ATP synthase complex opens
– H+ rush through – energy is
harnessed to make ATP
III. Anaerobic cellular respiration –
without oxygen
A. Alcoholic fermentation
1. C6H12O6  2C2H5OH
(ethanol) + 2CO2 + 2ATP
2. yeast – fungus (unicellular)
B. Lactic acid fermentation
1. C6H12O6  2C3H6O3 +
2ATP
2. bacteria, human muscles
IV. Alternate metabolic pathways
A. Carbohydrates are metabolized
first, then lipids, then proteins
last
1. Lipids contain at least 2x
more energy than
carbohydrates
B. Lipids
1. lipids are broken down into
their monomers: glycerol
and fatty acids
2. glycerol  enter glycolysis
through several of the
intermediates
3. fatty acids may be converted
into acetyl-CoA
C. Proteins
1. proteins are broken down
into their monomers: amino
acids
2. amino acids may be
deaminated and then
converted into: pyruvate,
acetyl-CoA, various
intermediates of the Citric
Acid cycle
D. Catabolism vs Anabolism
1. catabolism – break down of
large, high energy molecules
to release energy (exergonic)
2. anabolism – synthesizing
large, high energy molecules
from simpler components
(requires energy –
endergonic)
3. Catabolism drives anabolism
4. Metabolic pool