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Study Notes on Cellular Respiration

Cellular Energy Sources

  • Cells utilize sugars, fats, and proteins as potential energy sources.

    • These organic molecules are used in the process of cellular respiration to generate ATP (adenosine triphosphate).

    • All these molecules provide high-energy electrons necessary for ATP production.

Overview of Cellular Respiration

  • Cellular respiration is detailed further in the study module and primarily occurs in mitochondria.

    • Key processes will involve glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation.

    • Fundamental course: BIOL 1103 Foundations of Biology I, presented by Iain McKinnell.

Energy Transformation in Cells

  • Energy Transformation Requirements

    • Cells need various organic molecules as energy sources due to their ability to provide high-energy electrons.

  • Redox Reactions

    • A redox (reduction-oxidation) reaction is defined as a chemical reaction in which the oxidation states of atoms are changed.

    • Oxidation involves the loss of electrons; Reduction involves the gain of electrons.

    • The acronym OIL RIG is used: Oxidation Is Loss; Reduction Is Gain.

Electron Carriers in Energy Transfer

  • Electron carriers play a critical role in transporting electrons and facilitating energy release during cellular respiration.

    • Example: NAD+ (Nicotinamide adenine dinucleotide) accepts electrons and is reduced to NADH.

  • The process leads to ATP generation, primarily through the electron transport chain (ETC).

Aerobic Respiration and Glucose Metabolism

  • Oxidation of Glucose

    • Glucose is oxidized to carbon dioxide (CO₂), whereas oxygen (O₂) is reduced to water (H₂O).

    • Mechanism encompasses several stages: glycolysis, pyruvate oxidation, and the citric acid cycle.

  • Glycolysis

    • Breakdown of glucose occurs here, involving an Energy Investment Phase and an Energy Payoff Phase.

Stages and Reactions of Glycolysis

  • Energy Investment Phase

    • 2 ATP molecules are used to initiate glycolysis.

  • Energy Payoff Phase

    • Production of 4 ATP through substrate-level phosphorylation, and reduction of NAD+ forms NADH.

    • Resulting molecules: 2 pyruvate and H₂O.

Pyruvate Oxidation and Citric Acid Cycle

  • Pyruvate Oxidation

    • Each pyruvate undergoes modifications, resulting in Acetyl CoA and CO₂ release.

  • Citric Acid Cycle (Krebs Cycle)

    • Processes Acetyl CoA to produce NADH, FADH₂, ATP, and releases CO₂.

    • Key outputs: 3 NADH, 1 FADH₂ per cycle.

Electron Transport Chain (ETC) Function

  • Role of ETC

    • Receives electrons from NADH and FADH₂, leading to O₂ reduction.

    • Oxygen acts as the final electron acceptor, forming water.

  • Proton Motive Force

    • Energy released during electron transport is used to pump protons (H⁺) from the mitochondrial matrix into the intermembrane space, establishing a gradient.

ATP Production via Chemiosmosis

  • Chemiosmosis

    • Protons flow back into the matrix through ATP synthase, driving the production of ATP from ADP and inorganic phosphate (Pi).

  • Oxidative Phosphorylation

    • The majority of ATP (approximately 30 molecules) derived from glucose is produced via this process, coupled with the ETC.

Disruptions to Cellular Respiration

  • Analysis of scenarios affecting cellular respiration, including the effects of inhibitors (e.g., cyanide, DNP) and their mechanism.

    • Cyanide blocks electron transfer, leading to cellular suffocation despite normal oxygen levels.

    • DNP acts as an uncoupling agent, affecting ATP synthesis due to its effect on the proton gradient.

Anaerobic Respiration and Fermentation

  • Anaerobic Respiration

    • Occurs in the absence of oxygen; prokaryotes utilize alternative electron acceptors (e.g., sulfate).

  • Fermentation

    • Includes lactic acid fermentation and alcohol fermentation, allowing cells to regenerate NAD+ from NADH in anaerobic conditions.

    • Lactic acid fermentation converts pyruvate to lactate; alcohol fermentation converts pyruvate to ethanol and CO₂.

  • Obligate vs. Facultative Anaerobes

    • Obligate anaerobes are harmed by oxygen, while facultative anaerobes can switch between aerobic respiration and fermentation.

Cancer Metabolism and Glycolysis

  • Cancer cells often enhance glycolysis to meet high energy and biosynthetic demands, using glucose transporter GLUT-1 for increased glycolytic activity.

Regulation of Cellular Respiration

  • Cellular respiration is subject to feedback mechanisms that regulate metabolic pathways to maintain homeostasis.

    • Key regulatory points occur in glycolysis, the citric acid cycle, and oxidative phosphorylation processes.

Review and Key Concepts

  • Importance of C-H and C-O bonds in energy storage.

  • Identifying oxidizing and reducing agents in redox reactions.

  • Mechanistic differences between substrate-level phosphorylation and oxidative phosphorylation.

  • Predicting outcomes associated with ETC dysfunction and the implications for ATP production in various metabolic pathways.