Chapter 9: Cellular Respiration
Chemical Energy and Food

A calorie is the energy
required to raise 1g of
water 1˚C
–

1g of glucose releases
3811 calories
1 Calorie (capital “C”) on
food labels is actually a
kilocalorie (1000 calories)
–
1g of glucose releases
3.811 Calories
Using Chemical Energy


Plants and animals both use
glucose for metabolic fuel
Glucose is not directly usable
–
Must be converted into ATP
first
Cellular Respiration Overview



Converts glucose into ATP
Occurs in both plants and
animals
Cellular Respiration
Reaction:
–

C6H12O6 + 6O2 → 6CO2 + 6H2O
Opposite of photosynthesis
- 6CO2 + 6H2O → C6H12O6 + 6O2
Glycolysis


Series of reactions which break a 6-carbon glucose
molecule into two 3-carbon molecules called pyruvic
acid (a.k.a. pyruvate)
Occurs in the cytoplasm
Glucose
2 G3P
2 Pyruvate
to electron
transport chain
Glycolysis


Process is ancient
– all organisms from simple bacteria to humans perform
it the same way
Yields 2 ATP and 2 NADH per glucose molecule
Glucose
2 G3P
2 Pyruvate
to electron
transport chain
Glycolysis
Overview:
 Glucose is converted
into 2 pyruvic acid
molecules
–

A.K.A. pyruvate
Pyruvic acid is a
reactant in the Krebs
Cycle
Glycolysis
Step 1:
 The cell invests 2 ATP
to convert glucose  2
G3P
Glycolysis
Step 2:
 4 ATP molecules are
produced from the
conversion of 2 G3P 
2 pyruvic acid
 2 NADH molecules are
produced
–
Used in E.T.C.
Glycolysis
Aerobic Cellular Respiration


Oxygen required = aerobic
2 more sets of reactions which occur in a
specialized organelles called mitochondria
1. The Krebs Cycle
2. The Electron Transport Chain
The Krebs Cycle


AKA The Citric Acid Cycle
Completes the breakdown of glucose
–

Carbon and oxygen atoms end up in CO2 and H2O,
respectively
Produces only 2 more ATP
–
but produces electron carriers NADH and FADH2
which move to the 3rd stage (The Electron Transport
Chain)
The Krebs Cycle
Citric Acid
Production
The Krebs Cycle
Products (per glucose):
 6 CO2
 2 ATP
 8 NADH
to E.T.C.
 2 FADH2
Electron Transport Chain



Powered by electron carriers from the Kreb’s
Cycle
Produces a total of 32 ATP
Water is formed when oxygen combines with
protons
The Electron Transport Chain
Hydrogen Ion Movement
Electron Transport
H+ Active Transport
H+ Diffusion
Intermembrane
Space
ATP synthase
Inner Membrane
Mitochondrial Matrix
ATP Production
Energy Tally


36 ATP for aerobic vs. 2 ATP for anaerobic
–
Glycolysis
2 ATP
–
Krebs
2 ATP
–
Electron Transport Chain
32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but
are important for global recycling of carbon
Anaerobic Cellular Respiration


Also called fermentation
Some organisms thrive in environments with little or no
oxygen
–


No oxygen used = anaerobic
Results in no more ATP
–

Marshes, bogs, digestive tracts, sewage treatment tanks, etc.
The final steps in these pathways serve ONLY to regenerate
NAD+ so it can keep glycolysis running
End products such as ethanol and CO2 (yeast in
beer/bread) or lactic acid (muscle cells)
Fermentation Overview
Alcoholic Fermentation



Used by yeasts and other microorganisms
Produces carbon dioxide and ethanol
Used to make bread and alcoholic drinks (beer, wine,
etc.)
Lactic Acid Fermentation



Used by both unicellular and multicellular organisms
Lactic acid buildup in muscles causes a burning sensation
Used in the production of sour cream, cheese, yogurt, and
many other foods & beverages
Glucose
Pyruvic Acid
Lactic Acid
Fermentation Overview