BIOLOGI SMA Kelas 12 - Metabolisme Part 2 (Katabolisme) | GIA Academy

Catabolism and Cellular Respiration

Catabolism breaks complex molecules into simpler ones, releasing energy that is captured mainly as ATP and used to power cellular activities. Anabolism, by contrast, builds complex molecules from simpler ones and requires energy.

Cellular respiration is a catabolic process that uses food molecules—especially glucose—to produce ATP. It can be divided into aerobic respiration, which requires oxygen, and anaerobic respiration (fermentation), which occurs without oxygen.

Aerobic Respiration

Aerobic respiration requires oxygen. In eukaryotic cells, its stages take place in the cytosol and mitochondria. Prokaryotes carry them out without mitochondria. The video describes four stages:

1. Glycolysis

   • Takes place in the cytosol.
   • Breaks one glucose molecule into two pyruvate molecules.
   • Uses ATP in the early reactions and produces ATP later.
   • Yields a net total of 2 ATP and 2 NADH per glucose.
   • The video divides glycolysis into nine stages: the early steps use ATP, while later steps generate ATP and NADH.

2. Oxidative decarboxylation

   • Takes place in the mitochondrial matrix in eukaryotes and the cytosol in prokaryotes.
   • Each pyruvate loses a carbon as CO₂ and is oxidized. The remaining two-carbon unit joins coenzyme A to form acetyl-CoA.
   • Produces 2 acetyl-CoA, 2 CO₂, and 2 NADH per glucose.

3. Krebs cycle (citric acid cycle)

   • Takes place in the mitochondrial matrix in eukaryotes and the cytoplasm in prokaryotes.
   • Acetyl-CoA combines with oxaloacetate to begin the cycle. Reactions release CO₂ and regenerate oxaloacetate, allowing the cycle to repeat.
   • The video gives a yield of 4 CO₂, 2 ATP, 6 NADH, and 2 FADH₂ per glucose.

4. Electron transport

   • Uses electrons and hydrogen ions carried by NADH and FADH₂ to drive ATP production.
   • The video uses the traditional estimates of 3 ATP per NADH and 2 ATP per FADH₂.
   • It states that eukaryotes yield 36 ATP because transferring NADH from glycolysis into mitochondria costs ATP, while prokaryotes yield 38 ATP. However, the video’s concluding recap also refers to 38 ATP, so its stated total is not fully consistent.

Anaerobic Respiration and Fermentation

Fermentation breaks down glucose without oxygen. It produces much less energy than aerobic respiration: 2 ATP per glucose, generated during glycolysis.

• Lactic acid fermentation

  • Occurs in muscle cells and Lactobacillus bacteria.
  • Glycolysis forms pyruvate, which is then converted into lactic acid. This process regenerates NAD⁺ for glycolysis.
  • The video lists 2 ATP and lactic acid as the final products.

• Alcohol fermentation

  • Occurs in yeast, including Saccharomyces cerevisiae.
  • Pyruvate releases CO₂ to form acetaldehyde, which is then reduced to ethanol. This process regenerates NAD⁺ for glycolysis.
  • The video lists 2 ethanol, 2 ATP, and 2 CO₂ per glucose.

Practice Questions

The video applies the material to two example questions:

• Glycolysis: The early steps require ATP, while later steps produce ATP. The stated net yield is 2 ATP and 2 NADH per glucose.
• Fermentation pathway: Lactic acid fermentation consists of glycolysis followed by the conversion of pyruvate into lactic acid. The pathway labels correspond to 2 ATP, pyruvate, and lactic acid.

Speaker or Source

• GIA Academy presenter/narrator — the sole speaking voice; no individual presenter is identified in the subtitles.