Cellular Respiration

The Organic Chemistry Tutor・2 minutes read

Cellular respiration converts glucose into ATP through a series of stages like glycolysis, pyruvate oxidation, the Krebs cycle, and the electron transport chain, generating energy efficiently through the gradual release of ATP. The process involves the production of carbon dioxide, water, and ATP, with oxygen serving as the final electron acceptor to create a maximum net output of 36 ATP molecules per glucose molecule.

Insights

  • ATP, the cell's energy currency, is crucial in cellular respiration, capturing energy in manageable steps to increase efficiency and minimize energy loss as heat, making it more advantageous than directly using glucose energy.
  • The Krebs cycle, a vital part of cellular respiration, converts acetyl coenzyme A into carbon dioxide, generating NADH and FADH2 for the electron transport chain, ultimately producing a substantial amount of energy in the form of ATP.
  • The electron transport chain, a key component of cellular respiration, facilitates the movement of electrons to create a positive charge gradient for ATP synthase to produce ATP through chemiosmosis, highlighting how cells efficiently generate energy from food molecules.

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Recent questions

  • What is cellular respiration?

    The process of deriving energy from food.

  • What is the role of ATP in cells?

    ATP serves as the cell's energy currency.

  • What are the stages of cellular respiration?

    Glycolysis, pyruvate oxidation, Krebs cycle, electron transport chain.

  • How does the electron transport chain produce ATP?

    By pumping protons and utilizing chemiosmosis.

  • What is the maximum ATP yield from cellular respiration?

    38 ATP molecules per glucose molecule.

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Summary

00:00

Cellular Respiration: ATP, Efficiency, and Stages

  • Cellular respiration is the process of deriving energy from food by reacting one molecule of glucose with six molecules of oxygen to produce six molecules of carbon dioxide and water, releasing a significant amount of energy.
  • Energy released in cellular respiration is partly captured in the form of ATP, which is the cell's energy currency, driving various cellular functions by transferring phosphate groups.
  • Cells use ATP instead of directly using glucose energy due to efficiency; ATP releases energy in small, manageable steps, reducing energy loss as heat and increasing the conversion of energy into useful work.
  • The analogy of an internal combustion engine in a car illustrates the efficiency of releasing energy gradually through ATP compared to a single explosive reaction, making smaller car engines more efficient than larger ones.
  • ATP's structure consists of a five-carbon ribose sugar, a nitrogenous base called adenine, and three phosphate groups, serving as the primary energy carrier in cells.
  • Cellular respiration comprises four stages: glycolysis, pyruvate oxidation, the Krebs cycle, and the electron transport chain, each occurring in specific cellular locations.
  • Glycolysis involves converting glucose into two pyruvate molecules, with an initial investment of two ATP molecules and a net gain of two ATP molecules per glucose molecule.
  • Enzymes in glycolysis include kinases for phosphate group transfer, isomerases for rearrangement reactions, and dehydrogenases for hydrogen removal, aiding in the conversion of glucose to pyruvate.
  • Pyruvate oxidation converts pyruvate into acetyl coenzyme A, involving a decarboxylation reaction and the enzyme pyruvate dehydrogenase for hydrogen transfer to NAD+.
  • The Krebs cycle occurs in the mitochondrial matrix, starting with the combination of acetyl coenzyme A and oxaloacetate to produce citric acid, generating NADH and FADH2 for the electron transport chain.

21:30

"Krebs Cycle: ATP Production and Electron Transport"

  • The Krebs cycle involves the oxidation of acetyl coenzyme A into two molecules of carbon dioxide, with oxaloacetate regenerating to pick up another acetyl coenzyme A.
  • Dehydrogenase enzymes catalyze the removal of hydrogen atoms from molecules, transferring them to carriers like NAD+ or FAD during the Krebs cycle.
  • The purpose of the Krebs cycle is to oxidize the acetyl group into carbon dioxide, with NADH and FADH2 picking up electrons for the electron transport chain.
  • One turn of the Krebs cycle produces three NADH molecules, one FADH2 molecule, and one ATP molecule, with GTP converting to GDP and ATP.
  • Glucose generates two pyruvate molecules, leading to two acetyl coenzyme A molecules and two turns of the Krebs cycle, resulting in six NADH, two FADH2, and two ATP molecules.
  • FAD is located in the inner membrane of the mitochondria, where succinate dehydrogenase enzyme operates, transferring electrons in the electron transport chain.
  • The mitochondria consists of an outer membrane, inner membrane, intermembrane space, and mitochondrial matrix, where the Krebs cycle and electron transport chain occur.
  • The electron transport chain involves the movement of electrons from complex 1 to complex 4, with mobile carriers like ubiquinone and cytochrome c facilitating electron transfer.
  • Protons are pumped from the mitochondrial matrix to the intermembrane space during the electron transport chain, creating a positive charge gradient for ATP synthase to generate ATP through chemiosmosis.
  • Oxidative phosphorylation combines oxidation of NADH and FADH2 with phosphorylation of ADP to produce ATP, with oxygen serving as the final electron acceptor due to its high electronegativity.

42:05

Cellular Respiration: ATP Production and Efficiency

  • NADH is oxidized to NAD+ in cellular respiration, passing electrons through complex 1, Q complex 3, and complex 4.
  • NADH activates three complexes, leading to the production of three ATP molecules per NADH molecule.
  • FADH2 activates two complexes, resulting in the production of two ATP molecules per FADH2 molecule.
  • Glycolysis yields a net of two ATP molecules and two NADH molecules.
  • One NADH molecule generates three ATP molecules, totaling six ATP molecules from glycolysis.
  • Two ATP molecules are needed to transport two NADH molecules into the mitochondria, resulting in a net yield of four ATP molecules from glycolysis.
  • Pyruvate oxidation produces two NADH molecules, yielding six ATP molecules.
  • The Krebs cycle generates one ATP molecule per turn, with one glucose molecule yielding two ATP molecules.
  • The Krebs cycle produces 18 ATP molecules from six NADH molecules and four ATP molecules from two FADH2 molecules.
  • One glucose molecule can yield a maximum of 38 ATP molecules in cellular respiration, with a net value of 36 ATP molecules after accounting for transportation costs.

01:05:22

Cellular Respiration: ATP Production and Processes

  • Anaerobic cellular respiration yields a maximum of two ATP molecules due to glycolysis.
  • Muscle cells produce lactate under anaerobic conditions, not ethanol.
  • Yeast cells produce ethanol under anaerobic conditions.
  • Pyruvate oxidation converts pyruvate to acetyl coenzyme A, involving decarboxylation.
  • NADH is a product of pyruvate oxidation, alongside acetyl coenzyme A.
  • ATP synthase is responsible for producing ATP during oxidative phosphorylation.
  • FADH2 transfers electrons to complex two in the electron transport chain.
  • NADH activates complex one, pumping protons into the intermembrane space, not the mitochondrial matrix.
  • Pyruvate oxidation does not result in lactate or ethanol production.
  • Oxygen is the final electron acceptor in aerobic cellular respiration, forming water as a final product.
  • ATP is the energy currency of the cell, transferring energy via phosphate group transfer.
  • Kinase enzymes typically transfer phosphate groups.
  • NADH dehydrogenase is complex one, while succinate dehydrogenase is complex two.
  • Chemiosmosis in the electron transport chain produces the most ATP molecules.
  • Pyruvate oxidation, the Krebs cycle, and the electron transport chain do not produce water, unlike glycolysis.

01:28:24

Cellular Respiration: ATP Production and Oxidation

  • During cellular respiration, water is produced in the electron transport chain as electrons from complex four react with oxygen gas and hydrogen ions to form water in the mitochondrial matrix.
  • Carbon dioxide is produced during pyruvate oxidation and the Krebs cycle, with one molecule of carbon dioxide released for every pyruvate molecule and two molecules of carbon dioxide produced for every acetyl coenzyme a molecule in the Krebs cycle.
  • ATP is a product of cellular respiration, generated as ADP with phosphate is converted into ATP, with a maximum theoretical yield of 38 ATP.
  • The electron transport chain receives electrons from NADH and FADH2, pumping hydrogen ions to the intermembrane space, while oxidation refers to a loss of electrons and reduction refers to a gain of electrons in redox reactions like cellular respiration.
  • Glucose is oxidized into carbon dioxide, while oxygen is reduced into water during aerobic cellular respiration, with the Krebs cycle producing two molecules of FADH2 for every molecule of glucose and four molecules of CO2 for every molecule of glucose.
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