Glycolysis, Embden-Meyerhof pathway (EMP)

Summary

This script explains the process of glycolysis, a ten-step metabolic pathway in which glucose is broken down to produce energy. It covers both the preparatory phase, where ATP is invested to modify glucose, and the payoff phase, where ATP and NADH are produced. The detailed sequence involves key enzymes like hexokinase, phosphofructokinase, and pyruvate kinase, which help convert glucose to pyruvate, generating energy for the cell. The script emphasizes the importance of glycolysis in energy production, particularly in anaerobic conditions, and highlights its role in cellular metabolism.

Takeaways

• 😀 Glycolysis is a ten-step reaction that explains how glucose is broken down to generate energy.
• 😀 It is important to study glycolysis because the food we consume, especially carbohydrates, provides glucose for energy production.
• 😀 Glycolysis consists of two phases: the preparatory phase and the payoff phase.
• 😀 In the preparatory phase, ATP is invested to prepare glucose for breakdown, starting with glucose converting to glucose 6-phosphate.
• 😀 Hexokinase enzyme catalyzes the conversion of glucose to glucose 6-phosphate, using ATP and producing ADP.
• 😀 Glucose 6-phosphate is converted into fructose 6-phosphate through isomerization, which allows for the addition of another phosphate group.
• 😀 Fructose 6-phosphate is then converted to fructose 1,6-bisphosphate, using ATP and the enzyme phosphofructokinase.
• 😀 The cleavage of fructose 1,6-bisphosphate results in two molecules: dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.
• 😀 In the payoff phase, glyceraldehyde 3-phosphate is converted to 1,3-bisphosphoglycerate, generating NADH in the process.
• 😀 ATP is produced during the later steps, where phosphate groups are transferred to ADP, ultimately leading to the formation of pyruvate and energy generation.
• 😀 Pyruvate kinase catalyzes the final step, where phosphoenolpyruvate is converted to pyruvate, generating ATP.

Q & A

What is glycolysis and why is it important?

Glycolysis is a 10-step biochemical pathway that breaks down glucose into pyruvate, releasing energy in the form of ATP. It is important because it provides cells with the energy necessary to perform vital functions, and it is the first step in cellular respiration.

What are the two main phases of glycolysis?

The two main phases of glycolysis are the 'Preparatory Phase' and the 'Payoff Phase'. In the preparatory phase, ATP is consumed to modify glucose, and in the payoff phase, ATP and NADH are produced as glucose is further processed into pyruvate.

What happens in the preparatory phase of glycolysis?

In the preparatory phase, two ATP molecules are consumed to phosphorylate glucose and its derivatives. This phase involves the conversion of glucose to glucose 6-phosphate, then to fructose 6-phosphate, and ultimately to fructose 1,6-bisphosphate, which is then split into two three-carbon molecules.

What is the role of the enzyme hexokinase in glycolysis?

Hexokinase is responsible for phosphorylating glucose to form glucose 6-phosphate, which is the first step in glycolysis. This phosphorylation uses ATP and prevents glucose from leaving the cell, keeping it available for energy production.

Why is the conversion of glucose 6-phosphate to fructose 6-phosphate necessary?

The conversion of glucose 6-phosphate to fructose 6-phosphate is necessary because it sets up the molecule for the addition of a second phosphate group at the first carbon, which will be crucial for further breakdown and energy production.

What is the significance of the enzyme phosphofructokinase?

Phosphofructokinase (PFK) plays a crucial regulatory role in glycolysis by adding a phosphate group to fructose 6-phosphate, converting it into fructose 1,6-bisphosphate. This step is a key point of control for glycolysis because PFK is highly regulated by energy levels in the cell.

What happens when fructose 1,6-bisphosphate is split into two three-carbon molecules?

When fructose 1,6-bisphosphate is split by the enzyme aldolase, it forms two three-carbon molecules: dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P). These molecules can be interconverted, with DHAP being quickly converted into G3P so that two molecules of G3P proceed to the next phase.

How is ATP generated during the payoff phase of glycolysis?

During the payoff phase, ATP is generated through substrate-level phosphorylation. In reactions catalyzed by enzymes like phosphoglycerate kinase and pyruvate kinase, phosphate groups are transferred from high-energy intermediates to ADP, forming ATP.

What is the role of NAD+ in glycolysis?

NAD+ plays an essential role in glycolysis by accepting electrons and hydrogen atoms during the oxidation of glyceraldehyde 3-phosphate, forming NADH. This process is crucial for maintaining the balance of redox reactions and for enabling the production of energy.

How does pyruvate kinase contribute to ATP production in glycolysis?

Pyruvate kinase catalyzes the final step of glycolysis, where phosphoenolpyruvate (PEP) donates a phosphate group to ADP, producing ATP and pyruvate. This is another instance of substrate-level phosphorylation and results in the net gain of 2 ATP molecules per glucose molecule.