Steps of glycolysis | Cellular respiration | Biology | Khan Academy

Summary

This video script offers an in-depth look at glycolysis, a vital biochemical pathway in cellular respiration found in all life forms. It details how glucose is broken down into two pyruvate molecules, generating a net gain of two ATPs and two NADHs. The script explores the investment phase using ATPs and the payoff phase producing ATPs, emphasizing the complexity of these processes happening continuously within our cells.

Takeaways

• 🌐 Glycolysis is a universal biochemical pathway found in almost all living organisms.
• 🍬 Glycolysis involves the breakdown of glucose, a six-carbon molecule, into two pyruvate molecules, each with three carbons.
• 💰 The process results in a net production of two ATP molecules after an initial 'investment' of two ATPs, hence a net gain of two ATPs.
• 🔋 During glycolysis, NAD+ is reduced to NADH, capturing electrons which can later be used in oxidative phosphorylation to produce more ATP.
• 🔄 The conversion from glucose 6-phosphate to fructose 6-phosphate is facilitated by the enzyme phosphoglucose isomerase, which helps in isomerization.
• 🔬 The enzyme phosphofructokinase adds a second phosphate group to fructose 6-phosphate, using another ATP in the process.
• ⚡️ Aldolase enzymes, such as fructose biphosphate aldolase, facilitate the cleavage of fructose 6-phosphate into two three-carbon chains.
• 🔄 Triosephosphate isomerase allows the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
• 🚀 The dehydrogenase enzyme plays a role in the reduction of NAD to NADH, adding a phosphate group to glyceraldehyde 3-phosphate.
• 🌱 Glycolysis is typically the first step in cellular respiration, leading to either the citric acid cycle and oxidative phosphorylation in the presence of oxygen or fermentation in its absence.
• 🧬 The script emphasizes the complexity and ubiquity of these biochemical reactions, highlighting their importance in cellular energy production.

Q & A

What is glycolysis?

Glycolysis is a biochemical pathway that occurs in nearly all living organisms and involves breaking down glucose into two pyruvate molecules, producing a net gain of two ATPs and reducing NAD to NADH.

How many carbons does glucose have and what does it get broken down into during glycolysis?

Glucose is a six-carbon molecule that gets broken down into two three-carbon pyruvate molecules during glycolysis.

What is the net production of ATP during glycolysis?

The net production of ATP during glycolysis is two ATPs, although four ATPs are produced, two are used in the process, hence the net gain is two ATPs.

What is the role of NADH produced in glycolysis?

The NADH produced in glycolysis can be used later in the electron transport chain during oxidative phosphorylation to produce more ATP.

What are the two phases of glycolysis?

The two phases of glycolysis are the investment phase, where two ATPs are used, and the payoff phase, where a net of four ATPs are produced.

What is the purpose of the investment phase in glycolysis?

The investment phase in glycolysis involves using two ATPs to phosphorylate glucose, which is necessary for the subsequent steps that lead to the production of ATP in the payoff phase.

What is the role of hexokinase in glycolysis?

Hexokinase is the enzyme that facilitates the first step of glycolysis by phosphorylating glucose, using an ATP in the process.

What is the role of phosphoglucose isomerase in glycolysis?

Phosphoglucose isomerase is the enzyme that catalyzes the conversion of glucose 6-phosphate to fructose 6-phosphate, changing the isomer form of the molecule.

What is the role of phosphofructokinase in glycolysis?

Phosphofructokinase is the enzyme that uses another ATP to add a second phosphate group to fructose 6-phosphate, which is part of the investment phase.

How does the aldolase enzyme contribute to glycolysis?

Aldolase enzymes, specifically fructose biphosphate aldolase, facilitate the breaking up of fructose 1,6-bisphosphate into two three-carbon chains, which are key intermediates in glycolysis.

What is the significance of the reduction of NAD to NADH in glycolysis?

The reduction of NAD to NADH is significant because NADH can be used in the electron transport chain to generate additional ATP, making it an important part of cellular energy production.