Reacción de acoplamiento para crear glucosa 6 fosfato | Biología | Khan Academy en Español

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15 Nov 201507:48

Summary

TLDRThe provided transcript discusses the significance of phosphorylating glucose in biological systems. Phosphorylation of glucose is crucial as it prevents the molecule from leaving the cell, allowing the cell to retain as much glucose as possible. The process begins with glucose-6-phosphate, a key molecule that initiates various cellular processes. However, phosphorylation is an endergonic reaction, requiring energy, which is provided by ATP. The coupling of ATP hydrolysis, an exergonic process, with the phosphorylation of glucose allows the reaction to proceed spontaneously under appropriate conditions. The transcript also highlights the role of enzymes, particularly hexokinase, in facilitating this reaction by reducing activation energy and managing electron repulsion. The presence of a magnesium ion within the enzyme structure aids in this process, enabling the nucleophilic attack necessary for the reaction. This overview underscores the importance of ATP as an energy currency and the vital role of enzymes in making energetically unfavorable reactions possible within biological systems.

Takeaways

🍬 **Phosphorylation of Glucose**: The process of adding a phosphate group to a glucose molecule is crucial in biological systems as it helps retain glucose within the cell.
🔒 **Negative Charge Retention**: Once glucose is phosphorylated, its negative charge makes it more difficult for the molecule to exit the cell, thus the cell retains more glucose molecules.
⚙️ **Energy Requirement**: The phosphorylation of glucose is an endergonic reaction, meaning it requires energy input and does not occur spontaneously.
💰 **ATP as Energy Currency**: The cell uses ATP (adenosine triphosphate) as its energy currency to facilitate the phosphorylation of glucose.
💥 **Coupling Reactions**: The phosphorylation reaction is coupled with the hydrolysis of ATP, making the overall process energetically favorable and spontaneous under the right conditions.
📉 **Energy Activation**: Even though the net reaction is exergonic, some activation energy is needed to initiate the reaction, which can be provided by enzymes.
🔬 **Role of Enzymes**: Enzymes, specifically referred to as exocin Asas in the script, play a vital role in reducing the activation energy and facilitating the reaction.
🧲 **Magnesium Ions**: The enzyme uses magnesium ions to help stabilize and manage the negative charges, allowing the nucleophilic attack to occur more readily.
⚡ **Nucleophilic Attack**: The mechanism involves a nucleophilic attack by the hydroxyl group on the phosphate, which is facilitated by the enzyme's ability to manage electron repulsion.
🔄 **Product Formation**: The end products of the coupled reaction are glucose-6-phosphate and ADP (adenosine diphosphate), which is energetically favorable.
🔗 **Importance of Enzymes**: Enzymes are essential in biological systems to lower activation energy and allow reactions that are not energetically favorable to proceed efficiently.

Q & A

Why is phosphorylation of glucose important in biological systems?
-Phosphorylation of glucose is important because it adds a phosphate group, which gives the glucose molecule a negative charge. This makes it more difficult for the glucose molecule to leave the cell, allowing the cell to retain as many glucose molecules as possible for energy and metabolic processes.
What is the role of glucose-6-phosphate in cellular processes?
-Glucose-6-phosphate is a crucial molecule that initiates a series of metabolic processes within the cell. It is a key intermediate in glycolysis and the pentose phosphate pathway, among other pathways.
Why does the phosphorylation of glucose require energy?
-The phosphorylation of glucose is an endergonic reaction, meaning it has a positive ΔG (Gibbs free energy) and does not occur spontaneously. It requires energy to proceed, which is provided by the hydrolysis of ATP.
How does ATP act as the cellular energy currency in the phosphorylation of glucose?
-ATP provides the necessary energy for the endergonic phosphorylation reaction by undergoing hydrolysis to ADP and an inorganic phosphate. This process is exergonic (releases energy) and makes the phosphorylation of glucose energetically favorable.
What is the role of an enzyme in facilitating the phosphorylation of glucose?
-An enzyme, specifically an exocin (such as hexokinase), facilitates the phosphorylation reaction by reducing the activation energy required for the reaction to occur. It does this by stabilizing the transition state and bringing the reactants closer together.
How does the presence of a magnesium ion assist in the phosphorylation process?
-The magnesium ion acts as a cofactor in the enzyme-catalyzed reaction, helping to stabilize the negative charges on the phosphate group and the glucose molecule. This reduces the activation energy and facilitates the nucleophilic attack by the glucose molecule on the phosphate.
What is the overall ΔG for the coupled reaction of ATP hydrolysis and glucose phosphorylation?
-The overall ΔG for the coupled reaction is calculated by summing the individual ΔG values of the ATP hydrolysis (negative) and glucose phosphorylation (positive). The result is -1.7 kJ/mol, indicating that the reaction is exergonic and can proceed spontaneously under the right conditions.
Why is it necessary to lower the activation energy for the phosphorylation reaction to occur?
-Lowering the activation energy allows the reaction to proceed more readily. Without the enzyme to facilitate the reaction and reduce the activation energy, the reaction would have a high activation energy barrier, making it less likely to occur.
How does the enzyme hexokinase help in the phosphorylation of glucose?
-Hexokinase, as an exocin, helps by providing a magnesium ion that interacts with the phosphate group of ATP and the glucose molecule. This interaction helps to stabilize the transition state and reduce the activation energy, allowing the reaction to proceed more efficiently.
What is the significance of the nucleophilic attack in the phosphorylation of glucose?
-The nucleophilic attack is the key step in the phosphorylation of glucose, where the glucose molecule attacks the phosphate group of ATP. This step is facilitated by the enzyme and the presence of the magnesium ion, leading to the formation of glucose-6-phosphate and ADP.
How does the hydrolysis of ATP relate to its role in providing energy for cellular processes?
-The hydrolysis of ATP to ADP and an inorganic phosphate releases energy, which is harnessed by the cell to perform various endergonic reactions, such as the phosphorylation of glucose. This process effectively couples the exergonic hydrolysis of ATP with other energy-requiring reactions.
What is the significance of the three-dimensional structure of enzymes in facilitating reactions?
-The three-dimensional structure of enzymes is crucial as it allows them to create a specific active site that can accommodate and interact with the substrate molecules in a precise manner. This spatial arrangement helps in stabilizing the transition state and reducing the activation energy, making the reaction more likely to occur.

Outlines

00:00

🔬 Phosphorylation of Glucose in Cellular Systems

This paragraph discusses the importance of phosphorylating glucose in biological systems. It explains that once glucose is phosphorylated, it becomes more difficult for the molecule to exit the cell, which is beneficial as cells aim to retain as many glucose molecules as possible. The process initiates a series of reactions within the cell. However, phosphorylation of glucose is an endergonic reaction, meaning it requires energy and will not occur spontaneously. To facilitate this, the cell uses ATP, the cellular energy currency, through a process analogous to ATP hydrolysis, which is energetically favorable and spontaneous under the right conditions. An enzyme, referred to as exocin Asa, is necessary to lower the activation energy and catalyze the reaction, resulting in the formation of glucose-6-phosphate and ADP. The net reaction is exergonic, meaning it releases energy, and can occur spontaneously, especially if the activation energy is reduced.

05:03

🌟 The Role of Enzymes in Facilitating Reactions

The second paragraph delves into the mechanism of the reaction without an enzyme, highlighting the difficulty due to the high activation energy and repulsion between the negative charges of oxygen atoms. It emphasizes the role of enzymes, specifically exocin Asa, which contains magnesium ions to help stabilize and occupy electrons, facilitating the nucleophilic attack necessary for the reaction to proceed. The paragraph uses an example to illustrate how enzymes, with their complex protein structures, can help in the reaction by shielding electrons with positive charges, thus reducing the activation energy and allowing the reaction to occur. It concludes by stressing the energetic favorability of the process, assuming the presence of an enzyme to distract the electrons, and provides insight into how ATP is useful in carrying out reactions that might not be energetically favorable on their own.

Mindmap

Keywords

💡Phosphorylation

Phosphorylation is the process of adding a phosphate group to a molecule, which in the context of the video, is glucose. This process is crucial as it allows the glucose molecule to be retained within the cell due to the newly acquired negative charge. The video emphasizes that phosphorylation is a key step in cellular processes, with glucose 6-phosphate being a significant molecule that initiates a series of reactions within cells.

💡Glucose

Glucose is a simple sugar that serves as a primary source of energy for cells. In the video, it is highlighted as the starting molecule that undergoes phosphorylation. The importance of glucose is underscored by its role in cellular metabolism and the fact that cells strive to retain as many glucose molecules as possible.

💡Glucose 6-phosphate

Glucose 6-phosphate is the product of phosphorylating glucose. It is a pivotal molecule that initiates various cellular processes. The video explains that glucose 6-phosphate is important because it is charged, which prevents it from easily leaving the cell, thus ensuring the cell can utilize the energy stored in glucose.

💡ATP (Adenosine Triphosphate)

ATP is the primary energy currency of the cell, which the video describes as a 'good friend.' It is used to provide the energy required for the endergonic reaction of glucose phosphorylation. The video illustrates how ATP is hydrolyzed into ADP (adenosine diphosphate) and a phosphate group, which is energetically favorable and spontaneous under the right conditions.

💡Hydrolysis

Hydrolysis, as mentioned in the video, refers to the process where ATP is broken down into ADP and a phosphate group. Although the script specifies that the reaction is not exactly a hydrolysis due to the absence of water, it is functionally similar and is an exergonic process that occurs spontaneously.

💡Endergonic Reaction

An endergonic reaction is one that absorbs energy from its surroundings. The video explains that the phosphorylation of glucose is an endergonic reaction with a positive ΔG (Gibbs free energy), meaning it does not occur spontaneously and requires an input of energy, which is provided by ATP.

💡Exergonic Reaction

An exergonic reaction is one that releases energy. The video describes the hydrolysis of ATP as an exergonic reaction, which is energetically favorable and occurs spontaneously under the right conditions. This is contrasted with the endergonic phosphorylation of glucose, which requires energy input.

💡Coupling Reactions

Coupling reactions involve linking two reactions so that the energy released from one can be used to drive the other. In the video, the hydrolysis of ATP is coupled with the phosphorylation of glucose to form glucose 6-phosphate. This coupling allows the endergonic reaction to proceed spontaneously by utilizing the energy from the exergonic reaction.

💡Energy of Activation

The energy of activation is the minimum energy required to initiate a chemical reaction. The video discusses how enzymes, such as exocin Asas, help to reduce this energy, making it easier for reactions like the phosphorylation of glucose to occur by keeping electrons busy with ions, such as magnesium.

💡Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering the energy of activation. In the video, the enzyme exocin Asas is mentioned as facilitating the phosphorylation of glucose by providing ions, like magnesium, to interact with the negatively charged oxygen atoms, thus making the nucleophilic attack on the phosphate group more feasible.

💡Nucleophilic Attack

A nucleophilic attack is a fundamental concept in chemistry where a nucleophile (an electron-rich species) donates a pair of electrons to an electrophile (an electron-poor species). In the context of the video, the nucleophilic attack refers to the oxygen in the hydroxyl group of glucose attacking the phosphate group to form glucose 6-phosphate.

Highlights

Phosphorylating a glucose molecule is very valuable in biological systems as it helps the cell retain more glucose molecules.

Once glucose is phosphorylated, it becomes negatively charged and harder for the molecule to exit the cell.

Glucose 6-phosphate is an important molecule that initiates a series of processes inside cells.

The glucose phosphorylation reaction is endergonic, meaning it requires energy and will not occur spontaneously.

The reaction has a positive ΔG, indicating it is not energetically favorable on its own.

To make the reaction occur, the cell uses ATP, the energy currency, through a process similar to ATP hydrolysis.

The hydrolysis of ATP to ADP and a phosphate group is energetically favorable and spontaneous under the right conditions.

An enzyme is needed to reduce the activation energy and facilitate the reaction by keeping the negatively charged oxygens occupied with ions.

The enzyme uses a magnesium ion to help in the nucleophilic attack of the oxygen on the phosphate.

The overall coupled reaction has a negative ΔG, making it exergonic and spontaneous with the enzyme's help.

The enzyme, specifically an exocin like ASA, plays a crucial role in facilitating the reaction by reducing the activation energy.

The coupled reaction produces glucose 6-phosphate, ADP, and inorganic phosphate, with the release of a phosphate group from ATP being energetically favorable.

The enzyme's 3D structure allows it to surround and interact with the substrates, facilitating the necessary nucleophilic attack.

ATP's release of a phosphate group is energetically favorable, but it can also drive reactions in the system that are not inherently energetically favorable.

The importance of enzymes in biology is highlighted, as they help lower activation energy and facilitate essential reactions.

The example of how ATP can be used to drive the phosphorylation of glucose, even though it is an endergonic reaction, demonstrates the versatility of ATP in cellular processes.

The reaction mechanism is discussed in detail, providing insight into the role of enzymes and the energetics of biochemical reactions.