Cellular Respiration — Comprehensive Notes Flashcards

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Cellular Respiration

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Process that breaks down glucose to produce usable cellular energy (ATP). It occurs mainly in the mitochondria of eukaryotic cells and powers all cellular functions. A single glucose can yield about $36$–$38$ ATP when oxygen is available.

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ATP

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Adenosine triphosphate (ATP) is the primary energy currency of the cell used to drive metabolic reactions. Cells expend ATP to perform work and regenerate it via cellular respiration. ATP hydrolysis releases energy that powers cellular processes.

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Glucose

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A six-carbon sugar that serves as the primary fuel for cellular respiration. Glucose is oxidized during respiration to release stored chemical energy that is converted into ATP. It is produced by photosynthesis in autotrophs.

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Oxygen

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Molecular oxygen ($O_2$) is the final electron acceptor in aerobic cellular respiration. At the end of the electron transport chain oxygen combines with electrons and protons to form $H_2O$. Without $O_2$, cells cannot run the full aerobic pathway and yield much less ATP.

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Products

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The main products of cellular respiration are $CO_2$, $H_2O$, ATP, and heat. Carbon dioxide is released when carbon atoms are stripped from glucose, and water is formed when oxygen accepts electrons at the end of the ETC. Heat is a byproduct of the energy transformations.

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Photosynthesis

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The process by which producers (autotrophs) convert light energy into chemical energy, producing glucose and $O_2$. Photosynthesis and cellular respiration are complementary: the products of one are the reactants of the other. This cyclical relationship links energy and carbon flow in ecosystems.

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Autotroph

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An organism that makes its own organic molecules (like glucose) from inorganic sources, typically via photosynthesis. Autotrophs are the producers that supply the chemical energy used by consumers. Examples include plants and many algae.

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Heterotroph

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An organism that obtains energy and carbon by consuming organic compounds produced by other organisms. Heterotrophs perform cellular respiration to extract ATP from consumed food. Animals, fungi, and many bacteria are heterotrophs.

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Mitochondria

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Organelles in eukaryotic cells that convert food energy into ATP, often called the cell’s powerhouse. They have an outer membrane and a highly folded inner membrane and contain their own DNA and ribosomes. Prokaryotes lack mitochondria and carry out respiration across their cell membrane.

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Outer Membrane

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The mitochondrion’s outer membrane acts as a protective barrier that controls what enters and exits the organelle. It helps define the organelle’s overall compartmentalization. Transport proteins in this membrane regulate passage of molecules.

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Inner Membrane

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The inner mitochondrial membrane is folded into cristae, increasing surface area for energy-producing reactions. Embedded protein complexes of the electron transport chain and ATP synthase reside here. Its structure is critical for establishing the proton gradient used to make ATP.

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Intermembrane Space

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The region between the outer and inner mitochondrial membranes where protons ($H^+$) accumulate during electron transport. This buildup creates a concentration and charge gradient that drives ATP synthesis. It is essential for chemiosmotic ATP production.

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Matrix

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The fluid-filled space enclosed by the inner mitochondrial membrane that contains enzymes, mitochondrial DNA, and ribosomes. The Krebs cycle and pyruvate oxidation occur in the matrix. The matrix provides the chemical environment for metabolic reactions.

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Glycolysis

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The first stage of cellular respiration occurring in the cytoplasm that breaks one glucose into two pyruvate molecules. Glycolysis is anaerobic and produces a net of $2$ ATP and $2$ NADH per glucose. It creates the substrates needed for further oxidation in mitochondria.

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Energy Investment

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An early phase of glycolysis in which the cell uses $2$ ATP molecules to phosphorylate and destabilize glucose. This investment primes glucose for splitting into two three-carbon molecules. The payoff phase later yields a larger ATP return.

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G3P Formation

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During glycolysis the six-carbon glucose is split into two three-carbon molecules called glyceraldehyde-3-phosphate (G3P). Each G3P is then oxidized in subsequent steps to produce ATP and NADH. Splitting enables parallel energy-harvesting reactions.

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Energy Harvest

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The phase of glycolysis where enzymes oxidize G3P to pyruvate, producing $2$ NADH and $4$ ATP total (yielding a net of $2$ ATP). High-energy electrons are captured in NADH to be used later in the electron transport chain. This phase converts chemical energy into usable carriers.

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Pyruvate Oxidation

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Step that occurs as pyruvate enters the mitochondrial matrix where each pyruvate loses a carbon as $CO_2$ and bonds to Coenzyme A to form Acetyl-CoA. This reaction produces NADH and prepares carbon skeletons for the Krebs cycle. It links glycolysis to the Krebs cycle.

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Acetyl-CoA

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A two-carbon molecule formed from pyruvate that enters the Krebs cycle by combining with a four-carbon acceptor. Acetyl-CoA is the activated form of the carbon unit that will be oxidized to release energy. It is a central metabolic intermediate.

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Krebs Cycle

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Also called the citric acid cycle; it occurs in the mitochondrial matrix and oxidizes Acetyl-CoA to $CO_2$. Two turns per glucose yield about $6\ CO_2$, $2$ ATP, $8$ NADH, and $2$ $FADH_2$. The cycle regenerates the four-carbon molecule that accepts Acetyl-CoA and supplies electron carriers for the ETC.

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Electron Transport Chain

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A series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH and $FADH_2$. As electrons move down the chain their energy pumps protons into the intermembrane space, creating a proton gradient. This process is the primary source of the proton motive force used to make ATP.

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Chemiosmosis

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The process where protons flow back into the mitochondrial matrix through ATP synthase, driving the synthesis of ATP from ADP and Pi. Electrons and protons combine with oxygen at the end of the chain to form $H_2O$. Chemiosmosis couples the proton gradient to ATP production.

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Proton Gradient

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A difference in proton ($H^+$) concentration and charge across the inner mitochondrial membrane generated by the ETC. This electrochemical gradient stores potential energy that ATP synthase converts into ATP as protons flow back into the matrix. It is essential for aerobic ATP production.

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NADH and FADH2

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Electron carrier molecules that store high-energy electrons produced during glycolysis, pyruvate oxidation, and the Krebs cycle. They deliver electrons to the electron transport chain where their energy is used to pump protons and drive ATP synthesis. NADH and $FADH_2$ are central to aerobic ATP yield.

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ATP Yield

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Aerobic cellular respiration produces about $36$–$38$ ATP per glucose molecule when oxygen is available, with most made by the electron transport chain and chemiosmosis. In the absence of oxygen (anaerobic conditions) only the $2$ ATP from glycolysis are produced. Oxygen availability largely determines the total energy recovered from glucose.

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Prokaryotes

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Bacteria and archaea are prokaryotes that lack mitochondria but still perform cellular respiration across their plasma membrane. They can generate proton gradients and ATP using membrane-embedded proteins. Their respiration pathways are spatially simpler but functionally analogous.

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Carbon Change Formula

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Equation used to calculate change in carbon from DataNuggets: $C_{gained} - C_{lost} = \Delta C$. This value is the dependent variable when evaluating carbon change across census intervals. It helps quantify net carbon accumulation or loss.