Major Steps of Aerobic Cellular Respiration

Overview of Aerobic Pathway

Aerobic cellular respiration is the process by which cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water. This process consists of three major steps, each occurring in specific locations within the cell.

• Glycolysis: Occurs in the cytosol; breaks down glucose into two molecules of pyruvate.

• Krebs Cycle (Citric Acid Cycle): Takes place in the mitochondrial matrix; further oxidizes pyruvate derivatives to produce electron carriers.

• Oxidative Phosphorylation: Occurs in the inner mitochondrial membrane; uses electron carriers to generate ATP via the electron transport chain and chemiosmosis.

Equation for Aerobic Respiration:

Conversion of Pyruvate to Acetyl CoA (Link Reaction)

Junction Between Glycolysis and Krebs Cycle

Before entering the Krebs cycle, pyruvate produced from glycolysis is converted into acetyl CoA in the mitochondrial matrix. This step is essential for the continuation of aerobic respiration.

• Pyruvate Transport: Pyruvate is transported from the cytosol into the mitochondrion via a transport protein.

• Decarboxylation: Each pyruvate loses a carbon atom, released as CO2.

• Reduction of NAD+: NAD+ is reduced to NADH, capturing high-energy electrons.

• Formation of Acetyl CoA: The remaining two-carbon fragment is attached to coenzyme A, forming acetyl CoA.

Products per glucose:

• 2 Acetyl CoA

• 2 NADH

• 2 CO2

Equation for Pyruvate Conversion:

Krebs Cycle (Citric Acid Cycle)

Location and Initial Steps

The Krebs cycle is a series of enzyme-catalyzed reactions occurring in the mitochondrial matrix. It completes the oxidation of glucose derivatives, generating electron carriers and ATP.

• Entry: Acetyl CoA combines with oxaloacetate to form citrate.

• Cycle Progression: Citrate is progressively oxidized, regenerating oxaloacetate and producing energy-rich molecules.

Main Steps and Products of the Krebs Cycle

Each turn of the cycle processes one acetyl CoA. Since one glucose yields two acetyl CoA, the cycle turns twice per glucose molecule.

• Decarboxylation: Two CO2 molecules are released per cycle turn.

• Electron Carrier Production: Three NADH and one FADH2 are produced per cycle turn.

• ATP Generation: One ATP (or GTP) is produced via substrate-level phosphorylation per cycle turn.

Summary Table: Products of Krebs Cycle per Glucose

Key Intermediates and Enzymatic Steps

• Citrate: Formed from acetyl CoA and oxaloacetate.

• Isocitrate: Citrate is rearranged to isocitrate.

• α-Ketoglutarate: Isocitrate is oxidized and decarboxylated to α-ketoglutarate, producing NADH and CO2.

• Succinyl CoA: α-Ketoglutarate is further oxidized, yielding another NADH and CO2.

• Succinate: Succinyl CoA is converted to succinate, generating ATP (or GTP).

• Fumarate and Malate: Succinate is oxidized to fumarate (producing FADH2), then to malate.

• Oxaloacetate: Malate is oxidized to regenerate oxaloacetate, producing NADH.

Equation for One Turn of the Krebs Cycle:

Importance of the Krebs Cycle

• Central Role: The cycle is central to cellular metabolism, providing precursors for amino acids and other biosynthetic pathways.

• Energy Production: Supplies high-energy electrons to the electron transport chain for ATP synthesis.

Oxidative Phosphorylation

Electron Transport and Chemiosmosis

Oxidative phosphorylation is the final stage of aerobic respiration, occurring in the inner mitochondrial membrane. It uses electrons from NADH and FADH2 to drive ATP synthesis.

• Electron Transport Chain (ETC): Electrons are transferred through a series of protein complexes, releasing energy.

• Proton Gradient: Energy from electron transfer pumps protons into the intermembrane space, creating an electrochemical gradient.

• Chemiosmosis: Protons flow back into the matrix through ATP synthase, driving the synthesis of ATP.

Equation for ATP Synthesis:

Summary Table: Location of Major Steps

Example: In muscle cells during aerobic exercise, glucose is metabolized through these steps to efficiently produce ATP for contraction.

Additional info: The notes have been expanded to include full cycle steps, equations, and context for self-contained study. The original images and fragmented notes have been synthesized into a coherent summary suitable for exam preparation.