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1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway

Fermentation

Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway

Fermentation: Videos & Practice Problems

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Topic summary

The fate of pyruvate depends on cellular conditions. Under anaerobic conditions, humans produce lactate, while yeast generates ethanol and carbon dioxide, crucial for fermentation. In aerobic conditions, pyruvate converts to Acetyl CoA for cellular respiration. Fermentation recycles NAD⁺ from NADH, allowing glycolysis to continue. Alcohol fermentation involves decarboxylating pyruvate to acetaldehyde, which is then reduced to ethanol. Lactic acid fermentation directly reduces pyruvate to lactate, regenerating NAD⁺. This process is vital for cells like red blood cells that rely solely on glycolysis.

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Fermentation

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Fermentation Video Summary

The fate of pyruvate, a key product of glycolysis, is influenced by the cellular conditions and the type of organism involved. Under anaerobic conditions in human cells, pyruvate is converted into lactate, while in yeast or under hypoxic conditions, it is transformed into ethanol and carbon dioxide, a process fundamental to alcohol fermentation and the production of beverages like beer. This fermentation process has historical significance, as it may have played a role in the development of human societies.

In aerobic conditions, pyruvate is further processed into Acetyl CoA, which is essential for aerobic cellular respiration. However, when oxygen is scarce, fermentation becomes crucial for regenerating NAD⁺ from NADH, allowing glycolysis to continue. Glycolysis itself converts one molecule of glucose (a 6-carbon sugar) into two molecules of pyruvate (3-carbon compounds), yielding a net gain of 2 ATP and 2 NADH.

During alcohol fermentation, pyruvate undergoes decarboxylation, where a carbon atom is removed in the form of carbon dioxide, resulting in acetaldehyde. This intermediate is then reduced by NADH to produce ethanol, effectively recycling NAD⁺ to sustain glycolysis. The reaction can be summarized as follows:

1. Pyruvate (C₃H₄O₃) → Acetaldehyde (C₂H₄O) + CO₂

2. Acetaldehyde + NADH → Ethanol (C₂H₆O) + NAD⁺

In contrast, lactic acid fermentation, also known as the Cori cycle, involves the direct reduction of pyruvate by NADH to form lactate and regenerate NAD⁺. This process is vital for cells like red blood cells, which rely solely on glycolysis and fermentation for energy. The reaction can be summarized as:

Pyruvate (C₃H₄O₃) + NADH → Lactate (C₃H₆O₃) + NAD⁺

Both fermentation pathways serve the essential function of maintaining glycolysis in the absence of oxygen, ensuring that cells can continue to produce energy even under challenging conditions.

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What is the main purpose of fermentation in cells?

The main purpose of fermentation in cells is to regenerate NAD⁺ from NADH, allowing glycolysis to continue in the absence of oxygen. During glycolysis, glucose is broken down into pyruvate, producing a net gain of 2 ATP and 2 NADH. Without oxygen, cells cannot use NADH in oxidative phosphorylation, leading to a shortage of NAD⁺. Fermentation solves this by converting NADH back to NAD⁺, ensuring a continuous supply for glycolysis. This process is crucial for cells like red blood cells, which rely solely on glycolysis for energy production.

How does alcohol fermentation differ from lactic acid fermentation?

Alcohol fermentation and lactic acid fermentation differ in their end products and the organisms that perform them. In alcohol fermentation, pyruvate is decarboxylated to form acetaldehyde, which is then reduced by NADH to produce ethanol and CO₂. This process is common in yeast and some bacteria. In contrast, lactic acid fermentation involves the direct reduction of pyruvate by NADH to form lactate. This process occurs in human muscle cells under anaerobic conditions and in certain bacteria. Both types of fermentation regenerate NAD⁺ to sustain glycolysis.

Why is NAD⁺ regeneration important in fermentation?

NAD⁺ regeneration is crucial in fermentation because it allows glycolysis to continue producing ATP in the absence of oxygen. During glycolysis, NAD⁺ is reduced to NADH. Without a mechanism to oxidize NADH back to NAD⁺, glycolysis would halt due to a lack of NAD⁺. Fermentation provides this mechanism by converting NADH to NAD⁺, either through the production of ethanol and CO₂ in alcohol fermentation or lactate in lactic acid fermentation. This ensures a continuous supply of NAD⁺ for glycolysis, enabling cells to produce energy anaerobically.

What are the end products of alcohol fermentation?

The end products of alcohol fermentation are ethanol and carbon dioxide (CO₂). During this process, pyruvate is first decarboxylated to form acetaldehyde, releasing CO₂. Acetaldehyde is then reduced by NADH to produce ethanol. This type of fermentation is commonly carried out by yeast and some bacteria. The primary purpose of alcohol fermentation is to regenerate NAD⁺ from NADH, allowing glycolysis to continue in the absence of oxygen.

What is the Cori cycle and its significance in lactic acid fermentation?

The Cori cycle is a metabolic pathway that involves the conversion of lactate produced in muscles during anaerobic glycolysis back to glucose in the liver. During intense exercise, muscles produce lactate from pyruvate via lactic acid fermentation to regenerate NAD⁺ and sustain glycolysis. Lactate is then transported to the liver, where it is converted back to glucose through gluconeogenesis. This glucose can be released into the bloodstream and taken up by muscles for energy. The Cori cycle is significant because it helps maintain blood glucose levels and provides a way to recycle lactate, preventing its accumulation in muscles.