Understanding Aerobic Respiration: A Detailed Breakdown

Understanding Aerobic Respiration

Aerobic respiration is a biological process that extracts energy from glucose and other organic compounds to create adenosine triphosphate (ATP) using oxygen.

The Four Stages of Aerobic Respiration

1. Glycolysis

   • Occurs in the cytoplasm.
   • A six-carbon glucose molecule is converted into two, three-carbon molecules of pyruvate.
   • This process occurs in the cytoplasm.
   • To initiate the process, two molecules of ATP are consumed. Four molecules of ATP and two molecules of NADH are produced.

2. Formation of Acetyl Coenzyme A

   • Involves shuttling pyruvate molecules into the mitochondrion.
   • Each pyruvate molecule is oxidized to carbon dioxide and a two-carbon acetyl group.
   • The carbon dioxide is released as a waste product, and the two-carbon acetyl group is bound to coenzyme A and transported into the mitochondrion.

3. The Citric Acid Cycle (Krebs Cycle)

   • Each of the two-carbon acetyl groups produced from the original glucose molecule is bonded to a pre-existing molecule of oxaloacetate to form citrate (citric acid).
   • These two citric acid molecules are gradually oxidized, and the hydrogen ions are bound to NAD to form NADH and to FAD to form FADH₂.
   • Oxaloacetate is produced when the last carbon atom is released in the form of carbon dioxide.
   • Two ATP molecules are synthesized for each glucose molecule entering the cell.

4. Electron Transport Chain and Chemiosmosis

   • The electrons removed from the molecules in glycolysis and the citric acid cycle follow a series of cytochromes on the mitochondrial membrane.
   • Hydrogen ions (protons) are pumped across the inner membrane of the mitochondrion.
   • These protons flow through ATP synthase enzyme molecules, releasing energy that drives the formation of 34 ATP molecules.

Sliding Filament Model of Muscle Contraction

During muscle contraction, the thin actin filaments slide over the thick myosin filaments. When calcium is present, the blockage of the active site of actin clears.

1. Step A: The active site on actin is exposed.
2. Step B: Power Stroke: The myosin head pivots, pulling the actin towards the center.
3. Step C: Detachment: The bridge detaches when a new ATP binds with the myosin.