Problem 56 - Objective Biology for NEET

Question

How many ATP are used/required in glycolysis or for the complete phosphorylation of a glucose molecule? (a) 4 (b) 2 (c) 6 (d) 8

Step-by-Step Solution

Answer

The number of ATP used/required in glycolysis or for the complete phosphorylation of a glucose molecule is 2. Therefore, the correct answer is (b) 2.

Step 1: Understanding Glycolysis

Glycolysis is the process in cell metabolism by which carbohydrates and sugars, especially glucose, are broken down, producing ATP and pyruvate. Glycolysis consists of two parts: The first part prepares the six-carbon ring of glucose for cleavage by ATP, while the second part extracts ATP from the three-carbon fragments.

Step 2: Energy Investment Phase

In the energy investment phase, two ATP are consumed. The first ATP is used in the conversion of glucose to glucose-6-phosphate and the second in the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. Therefore, two ATP molecules are used in this phase.

Step 3: Energy Payoff Phase

In the second phase of glycolysis - the energy payoff phase - energy is produced. However, there is no consumption of ATP in this phase. Therefore, the total number of ATP molecules used or required for the whole glycolysis process, including the phosphorylation of a glucose molecule, remains two.

Key Concepts

ATP consumption in glycolysis

Glycolysis is a crucial metabolic pathway where glucose, a six-carbon sugar, is broken down into smaller molecules. During this process, energy is transferred and stored in the form of ATP. ATP acts as the cellular energy currency, necessary for various biochemical reactions. The consumption of ATP in glycolysis is carefully orchestrated to ensure that the pathway is efficient.
In glycolysis, specifically, two ATP molecules are consumed. This consumption happens during the initial steps, particularly the energy investment phase, which ensures the breakdown of glucose is feasible.
Understanding the role of ATP consumption highlights how cells regulate energy use, making glycolysis an essential study topic in biochemistry. Students often question where and how much ATP is used, making it a critical point of focus when studying glycolysis.

Energy investment phase

The energy investment phase is the initial stage of glycolysis. It is characterized by the consumption of energy in the form of ATP to modify glucose for further breakdown. During this phase, two ATP molecules are used for two key reactions.

• The first ATP is consumed when glucose is phosphorylated into glucose-6-phosphate.
• The second ATP is used to convert fructose-6-phosphate into fructose-1,6-bisphosphate.

These energy-consuming reactions are vital for priming glucose, allowing it to be split into two three-carbon molecules in subsequent steps. By investing energy upfront, cells enable the generation of more energy later in the process.
Understanding the specific actions during the energy investment phase helps in grasping how cells efficiently convert glucose into usable energy.

Phosphorylation of glucose

Phosphorylation is a chemical process where a phosphate group is added to a molecule, crucial in energy transfer reactions. Within glycolysis, the phosphorylation of glucose is one of the first steps and involves the addition of a phosphate group to the glucose molecule.
This step is facilitated by hexokinase, an enzyme that catalyzes the reaction and utilizes an ATP molecule in the process.

• This action converts glucose into glucose-6-phosphate.
• Phosphorylation makes glucose more reactive and traps it within the cell.

Subsequently, the phosphorylated glucose undergoes further processing, contributing to its breakdown into pyruvate while generating energy.
Understanding phosphorylation helps to see why energy is initially invested in glycolysis and provides insight into the intricate processes cells use to manage energy efficiently.