Cellular Respiration
Chemical Pathways
Section 9-1
Allen
Biology I
Chemical Energy and Food
• Lots of energy present in food (glucose/other
compounds)
– Ex: 1 gram glucose = 3811 calories
– Calorie – amount of energy required to raise one
gram of water, one Celsius degree
– Cells release the energy in glucose and other food
compounds
Overview of Cellular Respiration
• “reverse photosynthesis”
– 6O2 + C6H12O6 → 6CO2 + 6H2O + energy
• Cellular respiration – process of breaking
down glucose and other food molecule in the
presence of “oxygen”
• Figure 9-2 (page 222)
Cellular Respiration
Glycolysis
• Glycolysis – one molecule of glucose is broken
in half, producing two molecules of pyruvic
acid and a 3-carbon compound
• See figure 9-3(page 223)
Glycolysis
• Key concepts:
– Occurs in the cytoplasm of cell
– No oxygen required for glycolysis to occur
– Glucose is broken down into two 3-carbon
pyruvates (pyruvic acid)
– Net production of 2 ATP, 2 NADH, and 2 pyruvate
molecules
Fermentation
• Cellular respiration will NOT occur (Krebs and
ETC) if oxygen is not present
• If oxygen is not present, fermentation will
occur
• Fermentation – releasing of energy from food
molecules by producing ATP in the absence of
oxygen
2 Types of Fermentation
• Alcoholic
• Lactic acid
Alcoholic Fermentation
• Pyruvic acid + NADH → alcohol + CO2 + NAD
• Causes bread to rise
• “anaerobic” – no oxygen present
Lactic Acid Fermentation
• Pyruvic acid is converted into lactic acid
• Pyruvic acid + NADH → lactic acid + NAD
• Ex: muscle cells
– Not enough ATP produced to lack of oxygen
– Cells begin to produce ATP by lactic acid
fermentation