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CHAPTER 7: CELLULAR RESPIRATION
LECTURE OUTLINE
7.1 Metabolism
The term catabolism is sometimes used to refer to the breaking down of molecules and the term
anabolism is sometimes used to refer to the building up of molecules.
Catabolism
Our food contains three nutrients that our bodies break down and use as energy sources:
carbohydrates, proteins, and fats.
Anabolism
Some of the building blocks for the synthesis of larger molecules come from
intermediates in the pathways of catabolism. Catabolism also supplies the energy
required for anabolism.
Breathing, Eating, and Cellular Respiration
Cellular respiration is the step-wise release of energy from molecules such as glucose,
accompanied by the use of this energy to synthesize ATP molecules. The air we inhale
when we breathe contains oxygen, and the food we digest after eating contains glucose,
both substrates for cellular respiration.
7.2 Overview of Cellular Respiration
The overall equation for cellular respiration shows the coupling of glucose breakdown to
ATP buildup.
NAD+ and FAD
NAD+ and FAD are coenzymes of redox reactions. They pick up electrons (and their
accompanying hydrogen nuclei) at specific enzymatic reactions and carry these electrons
to the electron transport chain.
Phases of Cellular Respiration
The phases of cellular respiration include glycolysis, the preparatory reaction, the citric
acid cycle, and the electron transport chain.
7.3 Outside the Mitochondria: Glycolysis
Glycolysis is the breakdown of glucose to two pyruvate molecules. It takes place in the
cytoplasm.
Energy-Investment Steps
Two ATP are used to activate glucose as glycolysis begins.
Energy-Harvesting Steps
Glycolysis breaks down glucose to two molecules of pyruvate, making ATP by substratelevel ATP synthesis. There is a net gain of 2 ATP from glycolysis.
7.4 Inside the Mitochondria
Preparatory Reaction
The preparatory reaction occurs inside the mitochondria. It produces the molecule from
pyruvate that can enter the citric acid cycle.
Citric Acid Cycle
The citric acid cycle is a cyclical metabolic pathway located in the matrix of
mitochondria. It oxidizes acetyl groups to carbon dioxide, making ATP by substratelevel ATP synthesis, and producing NADH + H+ and FADH2.
Electron Transport Chain
The electron transport chain is located in the cristae of the mitochondria. It is a series of
carriers that pass electrons from one to the other, resulting in energy that is stored as a
hydrogen ion gradient.
Organization of Cristae
The electron transport chain is located within the cristae of the mitochondria.
The complexes in the chain establish a hydrogen ion gradient between the matrix
and the intermembrane space. This gradient is used to synthesize ATP by
chemiosmosis.
Energy Yield from Cellular Respiration
The complete breakdown of glucose results in 36 or 38 total ATP.
Efficiency of Cellular Respiration
Approximately 39% of the available energy is usually transferred from glucose to
ATP.
7.5 Fermentation
When oxygen is not available, cells turn to fermentation. During fermentation, glycolysis is
followed by a reduction of pyruvate to lactate by NADH + H+.
Advantages and Disadvantages of Fermentation
Fermentation is essential to humans despite its low yield of ATP. However, lactate is
toxic to cells.
Energy Yield of Fermentation
Fermentation produces only two ATP by substrate-level ATP synthesis.