Chapter 7- Cellular Respiration and Fermentation- Biology in Focus

Key Concepts of Cellular Respiration

7.1 Catabolic Pathways Yield Energy by Oxidizing Organic Fuels

• Cells break down glucose and other organic fuels to yield chemical energy in the form of ATP.

• Catabolism involves the oxidation of organic molecules, producing energy through redox reactions.

• Fermentation is a partial decomposition of glucose without oxygen.

• Aerobic respiration is a complete oxidation of glucose in the presence of oxygen.

• Oxidation: loss of electrons (as glucose is oxidized to CO2). Reduction: gain of electrons (as O2 is reduced to H2O).

7.2 Glycolysis Harvests Chemical Energy by Oxidizing Glucose to Pyruvate

• Glycolysis is a process occurring in the cytosol that breaks down glucose into two molecules of pyruvate.

• Glycolysis consists of both an energy investment phase (where ATP is consumed) and an energy payoff phase (where ATP and NADH are produced).

The sentence refers to the results obtained from the process of glycolysis, which is the initial stage of cellular respiration that breaks down one gluco.se molecule During glycolysis, one molecule of glucose is converted into two molecules of pyruvate, which can then enter the mitochondrion for further processing. Additionally, glycolysis produces two molecules of NADH, a high-energy electron carrier, and it yields a net gain of two ATP molecules, which are used as an energy currency in cells. The phrases '

7.3 After Pyruvate is Oxidized, the Citric Acid Cycle Completes the Energy-Yielding Oxidation of Organic Molecules

• Pyruvate enters the mitochondrion and is converted to acetyl CoA before entering the citric acid cycle.

• The citric acid cycle produces NADH, FADH2, and ATP while releasing CO2 as a waste product.

• Each acetyl CoA results in the production of 3 NADH, 1 FADH2, and 1 ATP through substrate-level phosphorylation.

7.4 During Oxidative Phosphorylation, Chemiosmosis Couples Electron Transport to ATP Synthesis

• The electron transport chain (ETC) operates via a series of redox reactions where electrons move from NADH and FADH2 to O2, forming H2O.

• The energy released during electron transport is used to pump protons (H+) across the inner mitochondrial membrane, creating a proton-motive force.

• ATP synthase harnesses this flow of protons back into the mitochondrial matrix to generate ATP from ADP and inorganic phosphate (Pi).

7.5 Fermentation and Anaerobic Respiration Enable Cells to Produce ATP Without the Use of Oxygen

• In anaerobic conditions, cells can utilize fermentation to regenerate NAD+ by transferring electrons from NADH to organic molecules.

• Types of fermentation include:

  • Alcohol Fermentation: Pyruvate is converted to ethanol and CO2.

  • Lactic Acid Fermentation: Pyruvate is reduced directly by NADH to form lactate.

• These processes allow ATP to be produced through substrate-level phosphorylation.

7.6 Glycolysis and the Citric Acid Cycle Connect to Many Other Metabolic Pathways

• Glycolysis is a core metabolic pathway that can utilize various carbohydrates, proteins, and fats as substrates for energy production.

• Intermediates of glycolysis and the citric acid cycle can also feed into biosynthetic pathways, linking catabolic and anabolic reactions in the cell.

Overview of Cellular Respiration Processes

• Cellular respiration is divided into three main stages:

  1. Glycolysis

  2. Pyruvate oxidation and Citric Acid Cycle

  3. Oxidative Phosphorylation

Energy Yield from Cellular Respiration

• In aerobic respiration, complete oxidation of one glucose molecule can yield up to ±32 ATP molecules, with approximately 90% produced during oxidative phosphorylation.