Reaction coupling to create glucose 6 phosphate | Biology | Khan Academy

Summary

The video explains how glucose phosphorylation is crucial in biological systems. Phosphorylating glucose, specifically forming glucose-6-phosphate, prevents glucose from leaving the cell and makes it available for cellular processes. This reaction requires energy, as it is endergonic, and is driven by ATP hydrolysis, which is exergonic. The enzyme hexokinase facilitates this reaction by lowering the activation energy, often using magnesium ions to distract electrons, allowing the nucleophilic attack on phosphate to proceed. This coupled reaction is exergonic and happens spontaneously with the enzyme's help, showing how ATP drives essential cellular functions.

Takeaways

• 🔬 Glucose phosphorylation is crucial for preventing glucose from leaving the cell after entering.
• 🧪 Phosphorylating glucose adds a negative charge, which makes it harder for glucose to pass through the cellular membrane.
• 💡 Glucose-6-phosphate is a key molecule involved in various cellular processes.
• ⚡ Phosphorylation of glucose requires energy, as the reaction is endergonic (has a positive delta-G).
• 🔋 ATP provides the necessary energy to drive this reaction by coupling its hydrolysis with glucose phosphorylation.
• 🔗 The enzyme hexokinase lowers the activation energy needed for the glucose phosphorylation reaction to occur.
• ⚙️ The mechanism involves nucleophilic attack by an electron pair on the glucose hydroxyl group onto the ATP's phosphorus atom.
• 🧲 Hexokinase utilizes ions like magnesium to help distract electrons and facilitate the reaction.
• 🔄 The reaction results in the formation of glucose-6-phosphate and ADP, making the process energetically favorable (exergonic).
• 💧 After the reaction, a water molecule can nab the remaining proton, finalizing the production of glucose-6-phosphate.

Q & A

Why is phosphorylating glucose important in biological systems?

Phosphorylating glucose is important because it traps the glucose inside the cell. Once glucose is phosphorylated to glucose-6-phosphate, it carries a negative charge, which makes it harder to pass through the cell membrane, allowing the cell to retain glucose for metabolic processes.

What is the role of ATP in the phosphorylation of glucose?

ATP provides the necessary energy for the phosphorylation of glucose. The reaction is endergonic, meaning it requires energy, which is supplied by the hydrolysis of ATP into ADP and a phosphate group.

Why is the phosphorylation of glucose considered an endergonic reaction?

The phosphorylation of glucose is considered endergonic because it requires energy input to occur. The reaction has a positive delta-G value, indicating it is not spontaneous.

How does coupling reactions help in the phosphorylation of glucose?

The phosphorylation of glucose is coupled with the hydrolysis of ATP, which is an exergonic reaction. By coupling the two reactions, the overall process becomes energetically favorable, with a net negative delta-G, allowing it to occur spontaneously.

What enzyme facilitates the phosphorylation of glucose, and how does it work?

The enzyme hexokinase facilitates the phosphorylation of glucose. It lowers the activation energy of the reaction by positioning the glucose and ATP correctly and using ions, such as magnesium, to stabilize negative charges, allowing the reaction to proceed.

What is the role of magnesium ions in the reaction catalyzed by hexokinase?

Magnesium ions help stabilize the negative charges on the ATP molecule, preventing repulsion of the electrons, and facilitating the nucleophilic attack required for the phosphorylation of glucose.

What is the net delta-G of the coupled reaction involving ATP and glucose?

The net delta-G of the coupled reaction involving ATP and glucose is approximately -16.7 kJ/mol, making the reaction exergonic and allowing it to happen spontaneously under the right conditions.

Why is the hydrolysis of ATP considered exergonic?

The hydrolysis of ATP is considered exergonic because it releases energy. The reaction has a negative delta-G, meaning it can occur spontaneously and provides energy for other cellular processes.

What role do enzymes like hexokinase play in lowering activation energy?

Enzymes like hexokinase lower the activation energy of reactions by positioning substrates correctly, stabilizing charges, and creating a favorable environment for the reaction to proceed, such as allowing nucleophilic attacks to occur more easily.

How does the glucose-6-phosphate structure differ from glucose after phosphorylation?

After phosphorylation, glucose-6-phosphate has an additional phosphate group attached to the 6th carbon. This phosphate group carries a negative charge, which differentiates it from unphosphorylated glucose.