Chapter 9
Biology
Sixth Edition
Raven/Johnson
(c) The McGraw-Hill Companies, Inc.
Cellular respiration is the step-wise release of energy
from molecules (usually carbohydrates) used to
synthesize ATP molecules.
Oxidation of glucose is an exergonic reaction
(releases energy) which drives ATP synthesis - an
endergonic reaction (energy is required).
Overall reaction for cellular respiration:
Drives ATP synthesis
NAD+ and FAD
• Each step of cellular respiration requires a
separate enzyme
• Some enzymes use the oxidation-reduction
coenzyme NAD+ or the coenzyme FAD.
The NAD+ cycle
Remember:
When NAD+  NADH it
has been reduced.
Remember:
When NADH  NAD+ it
has been oxidized.
4 Phases of Complete Glucose
Breakdown
•
•
•
•
Glycolysis - yields 2 ATP
Pyruvate oxidation – oxidation reaction
Krebs cycle – yields 2 ATP
Electron transport chain – yields 32-34 ATP
• Net ATP produced from respiration: 36-38
Outside the Mitochondria: Glycolysis
Universally found in all organisms.
Does not require oxygen.
Overview of Glycolysis
Glucose (6-C sugar)
2 ATP
2 ADP
6-C sugar diphosphate
3-C sugar-phosphate
2 ADP
3-C sugar-phosphate
2 ADP
2 ATP
2 NAD+
2 ATP
2 NAD+
2 NADH
2 NADH
3-C pyruvate
3-C pyruvate
Glycolysis summary
Inputs:
Glucose
2 NAD+
2 ATP
4 ADP + 4 P
Outputs:
2 pyruvate
2 NADH
2 ADP
4 ATP (2 net gain)
Pyruvate
(Oxygen present)
(Oxygen not present)
Cellular Respiration
Fermentation
Fermentation inputs and outputs per glucose
molecule
Inputs:
glucose
2 ATP
4 ADP + 4 P
Outputs:
2 lactate or 2 alcohol
and 2 CO2
2 ADP
4 ATP (2 net gain)
2-carbon molecule + 1
CO2
3-carbon molecule + 0
CO2
Pyruvate oxidation: if oxygen is present
2 NAD+
2Pyruvate + 2CoA
2 NADH + H+
2 Acetyl-CoA + 2CO2
Pyruvate is converted to a C2 acetyl group
attached to coenzyme A (CoA), and CO2 is
released. This occurs in the cytoplasm if
oxygen is present.
Krebs Cycle
• The Krebs cycle is a cyclical metabolic
pathway located in the matrix of the
mitochondria.
• At the start of the citric acid cycle, CoA
carries the C2 acetyl group to join a C4
molecule, and C6 citrate results.
Acetyl-CoA
(2 C)
C6
C4
NAD+
NADH
CO2
NADH
NAD+
Krebs cycle
C5
FADH2
NAD+
NADH
FADH
C4
CO2
ATP
ADP
+P
Krebs cycle inputs and outputs
per glucose molecule
Inputs:
2 acetyl groups
6 NAD+
2 FAD
2 ADP + 2 P
Outputs:
4 CO2
6 NADH
2 FADH2
2 ATP
Electron Transport Chain
• The electron transport chain located in the
cristae of mitochondria is a series of protein
carriers
• Electrons carried by NADH and FADH2 enter
the electron transport chain.
• As a pair of electrons is passed from carrier
to carrier, energy is released and is used to
form ATP molecules by oxidative
phosphorylation.
Oxygen receives energyspent electrons at the end
of the electron transport
system then combines
with hydrogen to form
water:
½ O2 + 2 e - + 2 H+ → H 2O
Glucose + O2  CO2 + H2O + ATP
Glycolysis
NAD+
Transition
Electron
Reaction
Transport
NADH
Chain
Krebs
Cycle
Remember: Electrons = Energy
Feedback
mechanisms
Acidic group
R-group
Amino group
H group
With Beta-oxidation
the last two carbons of
a fatty acid chain enter
the Krebs cycle.
This process is
repetitive until the
entire fatty acid chain
is consumed.
A 6 Carbon fatty acid
molecule produces
more ATP than a
glucose (based on the
amount of NADH and
FADH2 produced.
When PEP transfers a phosphate group to ADP, pyruvate is
formed. This is called substrate level phosphorylation.
ADP and PEP are substrates and an enzyme facilitates the
transfer of a phosphate group from PEP to ADP to create
ATP. The energy in the bond is conserved.
The End.