BackCellular Respiration: Citric Acid Cycle & Electron Transport System
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Cellular Respiration
Overview of Cellular Respiration
Cellular respiration is the process by which cells extract energy from nutrients, primarily glucose, to produce ATP, the energy currency of the cell. This process involves a series of metabolic pathways, including glycolysis, the citric acid cycle, and the electron transport system.
Glucose catabolism occurs in multiple stages, resulting in the production of ATP, CO2, and H2O.
ATP is produced through substrate-level and oxidative phosphorylation.
Coenzymes such as NAD+ and FAD play crucial roles in transferring high-energy electrons.
Citric Acid Cycle (Krebs Cycle)
Location and Sequence of Steps
The citric acid cycle occurs in the inner membrane region of the mitochondria. For each glucose molecule, the cycle operates twice, once for each acetyl group derived from glucose catabolism.
Acetyl CoA delivers acetyl groups to the cycle.
Acetyl combines with oxaloacetate to form citric acid.
Citric acid is metabolized, releasing CO2 and transferring electrons to NAD+ and FAD.
ATP is produced by substrate-level phosphorylation.
The cycle regenerates oxaloacetate for the next round.
Role of Coenzymes
Coenzymes are essential for energy production, acting as carriers for electrons and hydrogen ions.
NAD+ picks up hydrogen and electrons to become NADH.
FAD picks up hydrogen and electrons to become FADH2.
These coenzymes transport energy to the electron transport system.
Summary of Citric Acid Cycle
2 ATP molecules produced
6 NADH and 2 FADH2 generated
4 CO2 released as waste
Oxaloacetate regenerated
Electron Transport System (ETS)
Mechanism and ATP Production
The electron transport system is located in the inner mitochondrial membrane. NADH and FADH2 deliver electrons and hydrogen ions to carrier proteins, which transfer electrons through a series of reactions, pumping H+ ions across the membrane.
High concentration of H+ ions builds up outside the inner membrane.
H+ ions diffuse back through ATP synthase, catalyzing ATP formation from ADP and inorganic phosphate (Pi).
This process is called oxidative phosphorylation.
Spent electrons and H+ combine with O2 to form water.
Summary of Electron Transport System
Approximately 34 ATP molecules produced
6 molecules of water formed as waste
NAD+ and FAD are recycled
Energy Production Recap
Overall ATP Yield and Waste Products
Net gain of 36 ATP per glucose molecule (after accounting for 2 ATP used to shuttle NADH)
6 CO2 and 6 H2O produced as waste
Energy is released gradually for efficiency
Metabolism of Glycogen, Fats, and Proteins
Alternative Energy Sources
When glycogen stores are depleted, the body utilizes fats and proteins for ATP production. Fats provide the largest energy reserve, followed by proteins.
Glycogen: 1% of energy reserves
Fats: 78% of energy reserves
Proteins: 21% of energy reserves
Fat Catabolism
Triglycerides break down into glycerol and fatty acids
Glycerol can be converted to glucose or pyruvate
Fatty acids are converted to acetyl groups for the citric acid cycle
Fats produce about twice as much ATP as glycogen
Protein Catabolism
Proteins are broken into amino acids
Amine group (NH2) is removed and excreted as urea
Remaining carbon backbone enters the citric acid cycle
Protein catabolism increases during starvation, leading to muscle wasting
Anaerobic Respiration
Energy Production Without Oxygen
Anaerobic respiration allows cells to produce ATP in the absence of oxygen, primarily through glycolysis. Pyruvate is converted to lactic acid instead of entering the mitochondria.
ATP is produced for brief periods without oxygen
Lactic acid accumulation causes muscle burning and cramping
References
Johnson, M.D. (2017). Human biology: Concepts and current issues (8th ed). Pearson Education Inc.
