Cellular respiration is the process by which cells break down glucose and other food molecules in the presence of oxygen to harvest energy stored in ATP. It occurs in three stages: glycolysis, the Krebs cycle in the mitochondria, and the electron transport chain in the mitochondria. Mitochondria are the site of aerobic respiration and ATP production. Without oxygen, cells undergo fermentation which produces less ATP through pathways like lactic acid fermentation in muscles and alcohol fermentation in yeast.

1. Cellular Respiration

2. Harvesting energy stored in food
• Cellular respiration
– breaking down food to produce ATP
• in mitochondria
• using oxygen
food
– “aerobic” respiration
– usually digesting glucose
• but could be other sugars,
fats, or proteins
O2
glucose + oxygen → + carbon dioxide + water
C6H12O6
+
6O2
→
+ 6CO2 + 6H2O
ATP

3. Mitochondria
Located in plant and animal cells

4. What do we need to make energy?
• The “Furnace” for making energy
– mitochondria
• Fuel
– food: carbohydrates, fats, proteins
• Helpers
– oxygen
– enzymes
food
enzymes
• Product
– ATP
• Waste products
– carbon dioxide
• then used by plants
– water
O2
ATP
CO2
H2O

5. Chemical Structure of ATP

6. Cellular Respiration
C6H12O6 + 6O2  6 CO2 + 6 H2O + 36-38 ATP
•
•
•
•
Uses O2 (aerobic)
Starts in the cytoplasm but ends in mitochondria
Eukaryotic organisms
3 steps:
– Glycolosis
– Kreb’s cycle (citric acid cycle)
– Electron transport chain
• 36-38 ATP are produced

7. Metabolism of Glucose
•
•
•
•
A multistep pathway
Catalyzed by an enzyme at every step
Energy is transferred to ATP
3 major processes that are important for the
“harvest” of energy from glucose
– Glycolysis – splitting into pyruvic acid
– Fermentation - anaerobic
– Cellular Respiration - aerobic

8. cellular

9. Anaerobic Respiration
• Fermentation
– alcohol fermentation
• yeast
– glucose → ATP + CO2+ alcohol
– make beer, wine, bread
– lactic acid fermentation
• bacteria, animals
– glucose → ATP + lactic acid
– bacteria make yogurt
– animals feel muscle fatigue

10. Fermentation
C6H12O6 2CO2 + C2H5OH + 2 ATP
• Occurs in the cytoplasm of the cell
• NO O2 is present (anaerobic)
• Prokaryotic organisms (don’t have membrane-bound
organelles) and sometimes in eukaryotic*
• Two short fermentation pathways are the best
understood
– Lactic acid:
• End byproduct is lactic acid
– Alcohol:
• End byproduct is ethyl alcohol
• 2 ATP are produced

11. Lactic Acid Fermentation
• Occurs in many microorganisms & in some
muscle tissues*
• *Energy is needed for muscle contraction
– Blood cannot supply muscles with O2 fast
enough so muscle cells revert to lactic acid
fermentation
– Lactic acid build is what causes muscle
cramping

12. Alcohol Fermentation
• Occurs in some yeasts & plants cells under
anaerobic conditions
• Result is ethyl alcohol
• Alcohol beverages and bread are made using
this type of fermentation

13. Summary of Cellular Energy
Processes
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