9.1 An Overview of Cellular Respiration

• When glucose undergoes the uncontrolled oxidation reaction called burning, much of the potential energy stored in its chemical bonds is converted to kinetic energy in the form of heat and light.

• In glycolysis, one six-carbon molecule of glucose is broken into two molecules of the three-carbon compound pyruvate.

• Pyruvate processing: Each pyruvate produced by glycolysis is processed to release one molecule of C02, and the remaining two carbons are used to form the compound acetyl CoA.

• Citric αcid cycle: The two carbons from each acetyl CoA produced by pyruvate processing are oxidized to two molecules of C02.

• Electron transport αnd oxidαtive phosphorylαtion: Electrons from the NADH and FADH2 produced by pyruvate processing and the citric acid cycle move through a series of electron carriers that together are called an electron transport chain (ETC).

• The mode of ATP production links oxidation of NADH and FADH2 with phosphorylation of ADP, it is called oxidative phosphorylation.

• Cellular respiration is defined as any set of reactions that uses electrons harvested from high-energy molecules to produce ATP via an electron transport chain.

• Two of the most fundamental requirements of a cell are energy and carbon.

• By regulating key reactions involved in catabolic and anabolic pathways, the cell is able to maintain its internal environment even under different environmental conditions-a condition referred to as homeostasis.

9.2 Glycolysis: Oxidizing Glucose to Pyruvate

• An important advance in understanding how glycolysis is regulated occurred when biologists observed that high levels of ATP inhibit a key glycolytic enzyme called phosphofructokinase.

9.3 Processing Pyruvate to Acetyl CoA

• Portions of the inner membrane protrude into the interior of the organelle and expand to form sac-like compartments called cristae.

• The regions between the outer and inner membranes, including the space within the cristae, make up the intermembrane space. The compartment enclosed within the inner membrane is the mitochondrial matrix.

• Once pyruvate is inside the matrix, it is processed by an enormous and intricate enzyme complex called pyruvate dehydrogenase.

• The same enzyme complex then takes the two-carbon acetyl unit (-COCH3) and covalently bonds it to a compound called coenzyme A (CoA).

9.4 The Citric Acid Cycle: Oxidizing Acetyl CoA to CO2

• Carboxylic acids all have carboxyl functional groups by cells to fully oxidize the (R-COOH).

9.5 Electron Transport and Chemiosmosis: Building a Proton Gradient to Produce ATP

• Collectively, the molecules responsible for the oxidation of NADH and FADH2 are designated the electron transport chain (ETC).

• The inner membrane of the mitochondrion also contains a pool of non protein molecules called ubiquinone.

• The molecules involved in oxidizing NADH and FADH2 differ in their ability to accept electrons in a redox reaction. This ability is referred to as the redox potential of the electron acceptors.

• The researchers added the stalks and knobs back to vesicles that had been stripped of them and confirmed that the vesicles regained the ability to synthesize ATP. The entire protein complex is now known as ATP synthase.

• Mitchell introduced the term chemiosmosis to describe the use of a proton gradient to drive energy-requiring processes, like the production of ATP.

• In this situation, ATP production depended solely on the existence of a proton-motive force, which is based on a proton electrochemical gradient across a membrane.

• Organisms throughout the tree of life use electron transport chains and ATP synthases.

• The energy to produce ATP in oxidative phosphorylation comes from an established proton gradient, not phosphorγlated substrates as used in substrate level phosphorylation.

• Species that depend on oxygen as an electron acceptor for the ETC use aerobic respiration and are called aerobic organisms.

• Cells that depend on electron transport chains with electron acceptors other than oxygen are said to use anaerobic (“no air”) respiration.

9.6 Fermentation

• Fermentation is a metabolic pathway that includes glycolysis and an additional set of reactions that oxidize stockpiles of NADH to regenerate NAD+.

• Lactic acid fermentation, regenerates NAD+ by reducing pyruvate to form lactate, a deprotonated form of lactic acid.

• Organisms that can switch between fermentation and aerobic cellular respiration are called facultative anaerobes.