Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from organic molecules, primarily glucose, to produce adenosine triphosphate (ATP). This process occurs in several stages and is essential for life on Earth, as ATP serves as the universal energy currency for cellular activities.

• Key Equation: The overall reaction for aerobic cellular respiration is:

• Main Stages: Glycolysis, Pyruvate Oxidation, Citric Acid Cycle, and Electron Transport Chain/Chemiosmosis.

• Location: Glycolysis occurs in the cytosol; subsequent steps occur in the mitochondrion.

Glycolysis

Process and Phases

Glycolysis is the first step in cellular respiration, occurring in the cytoplasm. It breaks down one molecule of glucose (6 carbons) into two molecules of pyruvate (3 carbons each).

• Energy Investment Phase: 2 ATP are used to phosphorylate glucose and its intermediates.

• Energy Payoff Phase: 4 ATP and 2 NADH are produced.

• Net Yield: 2 ATP and 2 NADH per glucose molecule.

• No CO2 released during glycolysis.

Key Products: 2 Pyruvate, 2 ATP (net), 2 NADH

Pyruvate Oxidation

Conversion to Acetyl CoA

After glycolysis, pyruvate is transported into the mitochondrion, where it is oxidized to form Acetyl CoA. This step links glycolysis to the citric acid cycle.

• Each pyruvate (2 per glucose) produces:

  • 1 Acetyl CoA

  • 1 NADH

  • 1 CO2 (waste product)

• Enzyme Complex: Pyruvate dehydrogenase

Key Reaction:

Citric Acid Cycle (Krebs Cycle)

Oxidation of Acetyl CoA

The Citric Acid Cycle (also known as the Krebs Cycle) occurs in the mitochondrial matrix. It completes the oxidation of glucose derivatives, generating high-energy electron carriers.

• Per turn (per Acetyl CoA):

  • 1 ATP (or GTP)

  • 3 NADH

  • 1 FADH2

  • 2 CO2 (waste)

• Per glucose (2 turns): 2 ATP, 6 NADH, 2 FADH2, 4 CO2

Key Function: Supplies electrons (via NADH and FADH2) to the electron transport chain.

Electron Transport Chain & Chemiosmosis

ATP Production via Oxidative Phosphorylation

The Electron Transport Chain (ETC) is a series of protein complexes embedded in the inner mitochondrial membrane. Electrons from NADH and FADH2 are transferred through the chain, powering the movement of protons (H+) across the membrane, creating a proton gradient.

• Proton Gradient: The ETC uses the energy from electrons to pump H+ ions into the intermembrane space.

• ATP Synthase: Protons flow back into the matrix through ATP synthase, driving the synthesis of ATP from ADP and inorganic phosphate.

• Chemiosmosis: The process of using a proton gradient to generate ATP.

• Oxygen: Serves as the final electron acceptor, forming water.

Key Reaction:

Yield: Approximately 26-28 ATP per glucose via oxidative phosphorylation.

Summary Table: Major Steps and Yields of Cellular Respiration

Key Terms and Concepts

• ATP (Adenosine Triphosphate): The primary energy carrier in cells.

• NADH & FADH2: Electron carriers that store energy for the electron transport chain.

• Oxidation: Loss of electrons from a molecule.

• Reduction: Gain of electrons by a molecule.

• Chemiosmosis: The movement of ions across a semipermeable membrane, down their electrochemical gradient, coupled to ATP synthesis.

Example: ATP Yield from One Glucose Molecule

• Glycolysis: 2 ATP (net)

• Citric Acid Cycle: 2 ATP

• Oxidative Phosphorylation: ~26-28 ATP

• Total: ~30-32 ATP per glucose

Additional info: The first two slides and the journal article on smartphone addiction are not relevant to General Biology and have been omitted from these study notes. The notes focus on the biological process of cellular respiration as depicted in the provided lecture slides and images.