Question

How many ATP molecules are used in the initial steps of glycolysis?

Short answer

2 ATP molecules are used.

Step-by-step solution

- Understand Glycolysis

Glycolysis is the process in which one molecule of glucose is converted to two molecules of pyruvate. This process occurs in the cytoplasm of the cell and consists of two main phases: the investment phase and the payoff phase.

- Identify the Initial Steps

The initial steps of glycolysis are part of the investment phase. In the investment phase, energy is consumed in the form of ATP to prepare glucose for subsequent breakdown.

- Identify the ATP-Consuming Reactions

In the investment phase, ATP is used in two specific reactions: 1. The conversion of glucose to glucose-6-phosphate, catalyzed by the enzyme hexokinase, consumes one ATP.2. The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, catalyzed by the enzyme phosphofructokinase, consumes another ATP.

- Count the ATP Molecules Used

Add the number of ATP molecules used in the identified reactions. Since one ATP is used in each of the two reactions, a total of 2 ATP molecules are consumed in the initial steps of glycolysis.

Key concepts

glycolysis phases

Glycolysis is an essential metabolic pathway that converts one molecule of glucose into two molecules of pyruvate. This process occurs in the cytoplasm and is divided into two main phases:

• The investment phase
• The payoff phase

In the investment phase, the cell uses energy (ATP), while in the payoff phase, the cell gains more energy than initially invested. Understanding these phases is crucial for comprehending how cells extract energy from glucose.

investment phase

The investment phase of glycolysis is where the cell uses ATP to prepare glucose for subsequent breakdown. This phase consists of several steps that consume energy:

• Glucose is phosphorylated to glucose-6-phosphate.
• Glucose-6-phosphate is rearranged to fructose-6-phosphate.
• Fructose-6-phosphate is then phosphorylated to fructose-1,6-bisphosphate.

Because two molecules of ATP are used in these steps, it is called the investment phase. The goal here is to make glucose more chemically reactive and easier to split into two three-carbon molecules, which will later be processed in the payoff phase.

ATP consumption

ATP consumption is a critical aspect of the investment phase in glycolysis. During this phase, the cell uses two ATP molecules to ensure the efficient breakdown of glucose.

In the first reaction, an ATP molecule is used to convert glucose into glucose-6-phosphate. Another ATP molecule is used to convert fructose-6-phosphate into fructose-1,6-bisphosphate. These reactions are facilitated by enzymes, which play specific roles in catalyzing the conversion steps and ensuring the reactions proceed efficiently.

hexokinase

Hexokinase is a key enzyme in the initial step of glycolysis. It catalyzes the conversion of glucose into glucose-6-phosphate by transferring a phosphate group from ATP to glucose.

This reaction is crucial because it effectively traps glucose within the cell and prepares it for further breakdown in the subsequent steps of glycolysis. Without hexokinase, glucose would not be activated for metabolism, making it an essential enzyme for energy production in cells.

phosphofructokinase

Phosphofructokinase (PFK) is another critical enzyme in glycolysis. It acts in the second ATP-consuming step of the investment phase, where it converts fructose-6-phosphate into fructose-1,6-bisphosphate.

PFK is considered a rate-limiting enzyme, meaning it plays a vital role in regulating the speed of glycolysis. This enzyme is sensitive to cellular energy levels and can be regulated by various molecules, ensuring that glycolysis proceeds at an appropriate rate to meet the cell's needs for ATP production.