Learning Outcomes:
After completing this lesson, students will be able to:
i. Define anaerobic respiration and compare it to aerobic respiration.
ii. Explain the process of glycolysis and its role in both aerobic and anaerobic respiration.
iii. Describe the conversion of pyruvate into lactic acid or ethanol in anaerobic respiration.
iv. Identify the organisms that carry out anaerobic respiration.
Introduction:
Respiration is a fundamental process in living organisms, allowing them to extract energy from organic molecules to power their cellular activities. While most organisms rely on aerobic respiration, which requires oxygen, some organisms can survive and even thrive in the absence of oxygen. This alternative metabolic pathway is called anaerobic respiration.
i. Anaerobic Respiration vs. Aerobic Respiration:
Anaerobic respiration and aerobic respiration share some similarities, but they differ significantly in their final electron acceptor. In aerobic respiration, oxygen serves as the ultimate electron acceptor, while in anaerobic respiration, various organic molecules, such as pyruvate, lactate, or ethanol, act as electron acceptors.
ii. Glycolysis: A Common Pathway:
Both aerobic and anaerobic respiration begin with glycolysis, a series of ten enzymatic reactions that break down glucose, a six-carbon sugar, into two three-carbon molecules called pyruvate. This process occurs in the cytoplasm of cells and generates a small amount of ATP, the energy currency of cells.
iii. Fate of Pyruvate in Anaerobic Respiration:
In aerobic respiration, pyruvate enters the Krebs cycle and oxidative phosphorylation, processes that generate a significant amount of ATP. However, in anaerobic respiration, the absence of oxygen prevents pyruvate from entering the Krebs cycle. Instead, pyruvate undergoes fermentation, a process that regenerates the electron carriers NADH and NADPH, which are essential for glycolysis to continue.
iv. Lactic Acid Fermentation: In lactic acid fermentation, pyruvate is converted into lactate, an organic molecule that accumulates in muscles during strenuous exercise. The buildup of lactate is responsible for the burning sensation felt in muscles during intense activity.
v. Ethanol Fermentation: In ethanol fermentation, pyruvate is converted into ethanol, an alcohol, and carbon dioxide. This process occurs in some microorganisms, such as yeast, and is responsible for the production of alcoholic beverages.
vi. Organisms that Carry Out Anaerobic Respiration:
Anaerobic respiration is a common metabolic pathway among various organisms, including:
Bacteria: Many bacteria can survive and even thrive in the absence of oxygen, relying on anaerobic respiration for energy production.
Yeast: Yeast is a eukaryotic microorganism that undergoes ethanol fermentation, producing ethanol and carbon dioxide as byproducts.
Muscles: During intense exercise, muscle cells switch from aerobic respiration to anaerobic respiration due to the high demand for energy. The production of lactate during this process is responsible for muscle fatigue.
Anaerobic respiration is an alternative metabolic pathway that allows organisms to extract energy from organic molecules in the absence of oxygen. Glycolysis, a common pathway in both aerobic and anaerobic respiration, generates a small amount of ATP, while fermentation processes regenerate electron carriers and produce various organic molecules, such as lactate and ethanol. Anaerobic respiration is crucial for the survival and growth of many organisms, including bacteria, yeast, and muscle cells under conditions of limited oxygen availability.
