7.2

Energy Transfer in Redox Reactions

  • Redox reactions are responsible for the transfer of energy throughout biochemical processes.

    • Electrons are carriers of energy.

    • Hydrogen atoms (which include electrons) can also transfer energy.

Role of NAD+ in Cellular Respiration

  • NAD+ serves as an electron carrier in metabolic processes.

    • It accepts two electrons along with a proton, transforming into NADH.

Role of Oxygen

  • Oxygen acts as a terminal electron acceptor in cellular respiration.

ATP as an Energy Source

  • ATP (Adenosine Triphosphate) is the most commonly used energy source in biological systems.

  • Breaking down ATP releases energy, which can fuel other reactions:

    • When coupled with an endergonic reaction (which requires energy), an exergonic reaction (which releases energy, such as ATP breakdown) can provide the necessary energy.

Substrate-Level Phosphorylation

  • Substrate-level phosphorylation involves the transfer of a phosphate group to ADP (Adenosine Diphosphate) to form ATP.

    • Phosphorylation: adding a phosphate group to ADP results in ATP formation.

Overview of Cellular Respiration

  • Cellular respiration consists of four key reactions, with the first two being:

    1. Glycolysis:

    • Inputs glucose as a substrate.

    • Main Products:

      • 2 Pyruvate molecules

      • 2 NADH molecules

    • Location: Cytoplasm

  • The pyruvate produced from glycolysis moves into the mitochondria for further processing.

Pyruvate Oxidation

  • Pyruvate is oxidized to form Acetyl CoA.

    • Produces a by-product of CO2, which is considered a waste product.

    • The product that progresses to the next step is Acetyl CoA.

Mitochondrial Structure and Locations

  • Important areas within mitochondria for cellular respiration include:

    • Outer Membrane: Forms a barrier around the mitochondria.

    • Inner Membrane: Contains proteins involved in the electron transport chain.

    • Intermembrane Space: The space between the inner and outer membrane.

    • Matrix: Contains enzymes for the Krebs cycle and pyruvate oxidation.

Krebs Cycle (Citric Acid Cycle)

  • Acetyl CoA enters the Krebs cycle, which consists of nine reactions.

    • The process begins with Acetyl CoA combining with oxaloacetate to form citrate.

    • Rearranging citrate and decarboxylating two carbons release them as CO2.

  • Outputs for each Acetyl CoA:

    • 2 CO2 (waste)

    • 3 NADH (electron carriers)

    • 1 FADH2 (another electron carrier)

    • 1 ATP (via substrate-level phosphorylation)

  • Total yield of the Krebs cycle per glucose (accounting for two Acetyl CoA):

    • 4 ATP

    • 6 NADH

    • 2 FADH2

Electron Transport Chain (ETC)

  • Definition: A series of protein complexes located in the inner mitochondrial membrane through which electrons are transported.

  • Function: Extracts energy from NADH and FADH2:

    • Electrons flow through protein complexes, pumping protons (H+) from the mitochondrial matrix into the intermembrane space.

    • Oxygen serves as the terminal electron acceptor, combining with protons to form water (H2O).

    • If oxygen is not present, the chain ceases to function.

Chemiosmosis

  • Involves protons flowing back into the mitochondrial matrix through ATP synthase:

    • ATP synthase works like a turbine, producing ATP as protons flow through.

    • This process is described as chemiosmosis.

ATP Yield in Cellular Respiration

  • Total potential ATP production from one glucose molecule through cellular respiration can vary:

    • Theoretical maximum yield is approximately 36 ATP.

    • Actual yield is often lower due to inefficiencies; typical yield is closer to 30 ATP.

    • The large majority of ATP is produced during the electron transport chain and chemiosmosis.

Summary of ATP Production Steps

  • Energy yield from glycolysis and Krebs cycle feeds into the electron transport chain.

  • Thus, understanding these processes alongside mitochondrial structure supports comprehension of cellular energy production during respiration.

Questions

  • Encourage questions on discussed topics, especially focusing on the roles and relationships in cellular respiration.