Cellular Respiration
Chapter 7
Overview of Cellular Respiration
• Carbohydrates manufactured in photosynthesis
are broken down to produce ATP
• Organic molecules with many hydrogens are prime fuel
sources
• Oxidation reactions strip organic molecules of
hydrogens and electrons
• Used to power the creation of ATP
• Oxygen, highly electronegative, ultimately accepts
electrons and hydrogen to produce water
• Overall equation for cellular respiration:
C6H12O6 + 6 O2 +  6 CO2 + 6 H2O + “energy”
• Cellular respiration collectively refers to three
metabolic processes:
• Glycolysis
• The Citric Acid Cycle (Krebs Cycle)
• Oxidative Phosphorylation
The Mitochondrion
Glycolysis
• Occurs in cell’s cytosol in the cytoplasm
• No oxygen required
• Two phases:
• Energy Investment
• Uses ATP to phosphorylate the carbohydrate
• Energy Payoff
• Gains ATP by oxidizing the carbohydrate
• Electron carriers reduced
• NAD+ reduced to NADH
Glycolysis – Energy Investment
1. 2 ATP hydrolyzed to phosphorylate
carbohydrate
2. Unstable 6-carbon, 2-phosphate molecule splits
Glycolysis – Energy Payoff
1. Oxidation of 3-carbon, 1-phosphate molecule to
reduce NAD+ to NADH
• Additional inorganic phosphate added
2. 4 ADP phosphorylated to create 4 ATP
• Water released as waste product
3. Pyruvate is the end product
Glycolysis – Summary
The Citric Acid Cycle
• If oxygen is sufficient, pyruvate enters the
mitochondrion
• Pyruvate is modified upon entry
• Pyruvate + Coenzyme A (CoA) – CO2 = Acetyl CoA
• Transport into mitochondrion reduces 2 more electron
carriers
• Acetyl CoA enters the Citric Acid Cycle
• Occurs in mitochondrial matrix
The Electron Transport Chain
1. Electron carriers from glycolysis and Citric Acid
deliver electrons (2 per carrier) to E.T.C.
• E.T.C. = series of proteins embedded in membrane
• Uses energy from electrons to actively transport protons
(hydrogen ions) from one side of the membrane to the other
2. Electrons move from protein to protein towards
oxygen
• Final electron acceptor – highly electronegative
• 2 electrons + ½ O2 + 2 protons = H2O
3. Protons diffuse from the intermembrane space to
the matrix via ATP synthase
• ADP phosphorylated to create ATP
Summary of Cellular Respiration
• One molecule of glucose yields:
• Glycolysis
• 2 ATP
• 2 NADH
• The Citric Acid Cycle
• 2 ATP
• 6 NADH
• 2 FADH2
• Oxidative Phosphorylation
• About 26 – 28 ATP
Fermentation
• Insufficient oxygen prevents pyruvate from
entering mitochondrion
• Pyruvate is fermented
• Animals – lactic acid
• Bacteria & yeast – ethanol
The Cori Cycle
• Lactic acid builds up and causes a decrease in
blood pH (along with pain and muscle cramps)
• Lactic acid travels through the blood to the liver
• Liver cells “spend” 6 ATP to …
• Convert 2 lactic acids to 2 pyruvates …
• Then 2 pyruvates into glucose!
• Liver cells “sacrifice” their ATP to produce glucose
• Provides muscle cells with glucose to make ATP
temporarily
• Help in recovery from oxygen debt