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Energy - Releasing Pathways
Starr/Taggart’s
Biology:
The Unity and Diversity of Life,
Chapter 8
9e
Key Concepts:
All organisms can release energy stored in
glucose and other compounds and use it in
ATP production
Glycolysis can occur with or without
oxygen
Fermentation is an anaerobic process and
occurs in the cytoplasm
Aerobic respiration yields more energy
from glucose and occurs in the
mitochondria
Key Concepts:
Aerobic respiration has three stages
Photosynthesis and aerobic respiration are
linked on a global scale
Sunlight -----> Photosynthesis
6CO2 + 6 H2O
Aerobic
Respiration
C6H12O6 + 6O2
How Cells Make ATP
Photosynthesis
Glycolysis
Aerobic Pathways
Anaerobic Pathways
Fermentation
Overview of Aerobic
Respiration
Most ATP produced
Yield of 36 ATP or more
Summary:
C6H12O6 + 6O2 ------> 6CO2 + 6 H2O
Glucose
Oxygen
Carbon
Dioxide
Water
Respiration
Glycolysis
In cytoplasm
Krebs Cycle
In mitochondria
Electron Transport
System
In mitochondria
Glycolysis
 Glucose to Pyruvate
2 ATP needed to
start process
Substrate-level
Phosphorylation
NAD+ ---> NADH
End-Product
2 molecules of
pyruvate
Glycolysis
Glycolysis
Second Stage of the Aerobic
Pathway
Pyruvate enters
mitochondria
Krebs Cycle
Inner compartment
Electron Transport
Inner membrane
Second Stage Reactions:
Preparatory Steps
Pyruvate is stripped of a carboxyl group
which departs as carbon dioxide
It also gives up hydrogen and electrons to
NADP+ to form NADPH
Coenzyme A joins with remaining twocarbon fragment to form acetyl-CoA
Krebs Cycle
 Acetyl-CoA transfers its two carbon fragment to
oxaloacetate to start the cycle
During the cycle NAD+ and FAD are reduced to NADH and FADH2
Phosphate-level phosphorylation produces
ATP
 Oxaloacetate is regenerated
Carbon dioxide is released
Electron Transport
Phosphorylation
Innner membrane
H+ concentration
and electrical
gradients
ATP Synthases
Formation of ATP
from ADP and Pi by
H+ flow
Summary of the Energy
Harvest
 Glycolysis
2 ATP by substrate-level phosphorylation
2 NADH (used to form 4 ATP during third
stage)
 Krebs Cycle
2 ATP by substrate-level phosphorylation
 Electron Transport Phosphorylation
28 ATP by electron transport phosphorylation
Anaerobic Routes of ATP
Formation
Fermentation
pathways
Bacteria, yeasts
and protistans
Glycolysis - first
step
Net yield of two
ATP
Final product is
lactate or ethanol
Lactate Fermentation
Muscle cells in
animals
Quick ATP
production
Some bacteria
Alcohol Fermentation
Acetaldehyde is
intermediate
product
Yeasts
Anaerobic Electron Transport
Some bacteria
Cycling of sulfur, nitrogen and others
In plasma membrane
Inorganic compound serves as final
electron acceptor
Alternative Energy Sources in
the Human Body
Carbohydrates
Production of ATP from metabolism
Excess stored as glycogen in liver and muscle
cells
Fats
Triglycerides
Stored in adipose tissue
Can be used for energy
Proteins
Growth, maintenance, repair
Can be used for ATP production
In Conclusion
 Aerobic respiration, fermentation, and
other pathways release energy that
produce ATP
 NAD+ is the main coenzyme. FAD also is
involved
 Oxidation - reduction reactions are
involved
 Glycolysis is the start to all the pathways
 Net yield of Glycolysis is 2 ATP
In Conclusion
 Aerobic respiration involves two more
stages: Krebs cycle and electron transport
phosphorylation
 These steps proceed in the mitochondria
 Oxaloacetate combines with Acetyl-CoA to
start the Krebs cycle
 The electron transport system involves
delivery of H+ by coenzymes
In Conclusion
 H+ accumulate and gradients form across
the membrane
 Energy released during H+ flow drives the
formation of ATP
 Oxygen combines with H+ to form water
 Aerobic respiration yields 36 ATP for each
glucose molecule metabolized
 Fermentation is an anaerobic process
 Lactate fermentation yields 2 ATP
In Conclusion
 Alcohol fermentation yields 2 ATP
 Some bacteria use anaerobic electron
transport with inorganic compounds as the
final electron acceptor
 In some animals, sugars, fats, and amino
acids can enter the ATP-producing
pathways

developed by M. Roig