Bioquímica - Aula 12 - Glicólise e Fermentação

Summary

In this lesson, Professor Ângelo Cortel ASO explains the biochemical process of glycolysis, focusing on the breakdown of glucose into two molecules of pyruvate. He details the key reactions in glycolysis, including NADH production, ATP generation, and the enzymes involved. The process involves a series of energy investments and production, with NADH either being recycled through fermentation or aerobic respiration. The professor also touches on fermentation pathways (lactic and alcoholic), and their importance in industrial processes like bread-making and brewing. This lesson emphasizes the metabolic significance of glycolysis and its role in cellular energy production.

Takeaways

• 😀 Glycolysis is the process of breaking down glucose into pyruvate, producing ATP and NADH in the process.
• 😀 The glycolysis process occurs in several steps, involving enzymes that facilitate transformations like phosphorylation and oxidation.
• 😀 The first part of glycolysis includes the conversion of glucose into glyceraldehyde-3-phosphate, which is essential for subsequent reactions.
• 😀 The transformation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate involves the reduction of NAD to NADH.
• 😀 1,3-bisphosphoglycerate undergoes a reaction that generates ATP through the enzyme phosphoglycerate kinase.
• 😀 Isomerization of 3-phosphoglycerate to 2-phosphoglycerate occurs with a slightly positive delta G.
• 😀 The conversion of 2-phosphoglycerate into phosphoenolpyruvate generates water and has a positive delta G.
• 😀 The final step of glycolysis involves the conversion of phosphoenolpyruvate to pyruvate, producing ATP in the process.
• 😀 After glycolysis, pyruvate can either undergo fermentation or aerobic respiration depending on oxygen availability.
• 😀 In anaerobic conditions, fermentation processes such as lactic acid fermentation and alcoholic fermentation regenerate NAD, allowing glycolysis to continue.
• 😀 Lactic acid fermentation converts pyruvate into lactate, while alcoholic fermentation converts pyruvate into ethanol and CO2, both regenerating NAD+.
• 😀 The overall energy balance of glycolysis yields a net gain of 2 ATPs per glucose molecule, with a byproduct of NADH that is later re-oxidized during fermentation or aerobic respiration.

Q & A

What is the overall goal of glycolysis as discussed in the lecture?

The goal of glycolysis is to break down glucose (a six-carbon molecule) into two molecules of pyruvate (three-carbon molecules), generating ATP and NADH in the process.

How does the enzyme glyceraldehyde 3-phosphate dehydrogenase function in glycolysis?

Glyceraldehyde 3-phosphate dehydrogenase catalyzes the oxidation of G3P by NAD+, leading to the formation of 1,3-bisphosphoglycerate, which involves the reduction of NAD+ to NADH.

What is the significance of the reaction involving 1,3-bisphosphoglycerate and ADP?

In this reaction, 1,3-bisphosphoglycerate donates a phosphate group to ADP to form ATP and 3-phosphoglycerate. This step is crucial for ATP generation in glycolysis.

What is the role of ATP in the glycolytic pathway?

ATP is both consumed and produced during glycolysis. Initially, two ATP molecules are used to phosphorylate glucose and its intermediates, but later, four ATP molecules are generated, yielding a net gain of two ATP.

Why is it necessary for NAD+ to be regenerated during glycolysis?

NAD+ must be regenerated because it acts as a cofactor in several reactions of glycolysis, including the oxidation of G3P. Without NAD+, glycolysis would halt, preventing ATP production.

What happens in the fermentation process when oxygen is absent?

In the absence of oxygen, fermentation allows cells to regenerate NAD+ by reducing pyruvate to lactate (in lactic acid fermentation) or ethanol (in alcoholic fermentation), ensuring glycolysis can continue.

What is the difference between lactic acid fermentation and alcoholic fermentation?

In lactic acid fermentation, pyruvate is converted to lactate, regenerating NAD+. In alcoholic fermentation, pyruvate is first decarboxylated to acetaldehyde, which is then reduced to ethanol, also regenerating NAD+.

What is the function of pyruvate kinase in the final steps of glycolysis?

Pyruvate kinase catalyzes the final step of glycolysis, where phosphoenolpyruvate (PEP) donates a phosphate group to ADP, forming ATP and producing pyruvate.

What is the significance of the ΔG value for the glycolytic reactions?

The ΔG values of the reactions indicate whether they are exergonic (spontaneous) or endergonic (requiring energy). For example, reactions like the one involving phosphoenolpyruvate to pyruvate have a very negative ΔG, making them highly favorable and helping to drive glycolysis forward.

How does glycolysis contribute to the central metabolism of cells?

Glycolysis is a key step in the central metabolism of cells, providing both ATP for energy and intermediates like pyruvate, which can enter further pathways such as the citric acid cycle and oxidative phosphorylation for additional energy production.