Glucose Metabolism

GLUCOSE METABOLISM Study Notes

ENERGY STORAGE IN BONDS

  • Energy is stored within chemical bonds during reactions.

    • The energy stored in covalent bonds is approximately 98.8 kcal/mole.

    • Energy can be transferred to new bonds during chemical processes.

  • Electron Transfer:

    • Electrons may be transferred from one molecule or atom to another during these reactions.

    • When an atom or molecule loses an electron, it is said to be oxidized (this process is called oxidation).

    • Conversely, when an atom or molecule gains an electron, it is said to be reduced (this process is called reduction).

  • Redox Reactions:

    • Redox (reduction-oxidation) reactions are always coupled.

    • These reactions play a vital role in energy transfer within biological systems.

METABOLIC PATHWAYS

  • Definition: Metabolic pathways are formed by a series of chemical reactions.

  • Regulation:

    • Pathways are regulated by key enzymes which can be activated or inhibited, thereby influencing the rate of reactions.

    • Each specific reaction is catalyzed by a specific enzyme.

  • Compartmentalization: Metabolic processes are organized within particular cell compartments to enhance efficiency.

GLUCOSE METABOLISM

  • Overall Reaction:

    • Glucose ( ext{C}6 ext{H}{12} ext{O}_6) and O2 are converted to ATP, CO2, and H2O.

    • This process yields 686 kcal/mol of glucose.

  • Energy Generation:

    • Glucose metabolism drives the conversion of ADP and inorganic phosphate (Pi) to ATP.

ENERGY RELEASE AND CAPTURE DURING GLUCOSE METABOLISM

  1. By Redox Cofactors (Electron Carriers):

    • Key electron carriers include NAD+ and FAD, which can accept electrons and become reduced to form NADH and FADH2.

    • NAD+ accepts one hydrogen atom and one pair of electrons to become NADH.

  2. By Substrate-Level Phosphorylation:

    • ADP can accept a phosphate group, leading to ATP production.

PROCESSES INVOLVED IN GLUCOSE METABOLISM

  • Glycolysis:

    • Starting process occurring in the cytoplasm of cells.

    • Produces 2 pyruvate molecules and does not require O2.

  • Cellular Respiration:

    • An aerobic process that utilizes O2.

    • Converts each pyruvate into 3 CO2 molecules utilizing the energy stored in pyruvate to regenerate ATP.

  • Fermentation:

    • An anaerobic process where pyruvate is converted to either lactic acid or ethyl alcohol.

COMPARATIVE SUMMARY OF PROCESSES

  • Glycolysis: Produces:

    • 2 pyruvate

    • 2 ATP

    • 2 NADH (electron carriers)

  • Cellular Respiration includes:

    • Pyruvate oxidation

    • Citric Acid Cycle

    • Electron Transport Chain

    • Results in complete oxidation with waste products CO2 and H2O, yielding approximately 32 ATP with O2.

  • Fermentation results in:

    • Incomplete oxidation with waste products CO2 and either lactic acid or ethanol.

    • Yields only 2 ATP without O2.

REDOX REVIEW

  • If a substance is reduced, it acts as an oxidizing agent.

  • If a substance is oxidized, it acts as a reducing agent.

  • Specific Examples:

    • Glucose serves as a reducing agent.

    • O2 acts as an oxidizing agent.

GLYCOLYSIS PROCESS DETAILS

  • Occurs in the cytoplasm and involves 10 enzyme-catalyzed reactions.

  • Products of glycolysis include:

    • 2 pyruvate molecules

    • 2 ATP molecules

    • 2 NADH (as electron carriers)

PYRUVATE OXIDATION

  • After glycolysis, pyruvate diffuses into the mitochondrion where a series of coupled reactions occur:

    • Pyruvate, a 3-C molecule, is oxidized to form an acetyl group (a 2-C molecule), with the release of CO2.

    • The acetyl group binds with coenzyme A (CoA) to form AcetylCoA.

CITRIC ACID CYCLE

  • This cycle consists of 8 reactions.

    • Acetyl CoA is oxidized to produce 2 molecules of CO2.

    • Energy released from these reactions is captured by ADP and two electron carriers, NAD and FAD.

    • The citric acid cycle connects to the electron transport chain.

ELECTRON TRANSPORT CHAIN

  • Located in the inner mitochondrial membrane.

  • During earlier processes, electron carriers are reduced and then carry electrons into the chain.

  • Electrons are passed to a series of membrane-associated carriers, going through reducing and oxidizing states.

  • The flow of electrons drives the active transport of protons out of the mitochondrial matrix, establishing a proton gradient.

  • The diffusion of protons back into the matrix serves to drive the synthesis of ATP.