Biology Chapter 4: Cellular Respiration

Metabolism and Energy

• Metabolism encompasses all chemical reactions in an organism, vital for sustaining life.
• Two metabolic pathways: catabolism (breaks down molecules, releasing energy) and anabolism (builds molecules, requiring energy).
• Energy is the capacity to perform work; forms include electrical, light, radiant, and heat.

Energy Carrier Molecules

• ATP (adenosine triphosphate) serves as the universal energy currency, storing energy in phosphate bonds.
• Other energy carriers include NADH and FADH2 in cellular respiration, and NADPH in photosynthesis.

Cellular Respiration Overview

• Cellular respiration consists of three main processes: glycolysis, citric acid cycle, and oxidative phosphorylation.
• Takes place in both aerobic (requires oxygen) and anaerobic (does not require oxygen) conditions.

Glycolysis

• Occurs in the cytoplasm, where glucose is split into two molecules of pyruvate.
• Generates a net output of 2 ATP and 2 NADH.
• Non-oxygen dependent process, laying the groundwork for further energy extraction.

Citric Acid Cycle

• Takes place in the mitochondria, using pyruvate to generate ATP and energy carriers.
• Produces 3 CO2, 1 ATP, 4 NADH, and 1 FADH2 per pyruvate.
• Fully oxidizes glucose (all 6 carbons) to CO2, recycling the starting molecules to continue the cycle.

Oxidative Phosphorylation

• Occurs in the inner mitochondrial membrane; uses the electron transport chain (ETC) to produce ATP.
• Approximately 34 ATP generated, making this the most productive step of respiration.
• Oxygen is the final electron acceptor, forming water.

Importance of Oxygen

• Critical for accepting electrons in oxidative phosphorylation, linking respiration to aerobic environments.

Fermentation

• A process allowing organisms to generate ATP without oxygen, mainly through glycolysis.
• Lactic acid fermentation occurs in muscles under hypoxic conditions, producing lactic acid which leads to fatigue.
• Alcoholic fermentation, seen in yeast, produces ethanol and CO2.

Enzymes in Metabolism

• Biological catalysts composed of amino acids, speeding up reactions without being consumed.
• Enzymes exhibit specificity, binding to specific substrates, essential for maintaining homeostasis.

Key Learning Points

• Understand enzyme roles in metabolic pathways.
• Recognize the distinction between oxidative phosphorylation and fermentation.
• Identify ATP yield from each stage of cellular respiration—total of approximately 38 ATP per glucose molecule.