Ch.18 Metabolic Pathways and ATP Production

Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 13th Edition

Timberlake13th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9780134421353Not the one you use?Change textbook

Timberlake 13th Edition

Ch.18 Metabolic Pathways and ATP Production

Problem 21

Chapter 18, Problem 21

How is ATP used in the initial steps of glycolysis?

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Understand that glycolysis is the metabolic pathway that breaks down glucose into pyruvate, producing energy in the form of ATP and NADH. The initial steps of glycolysis are energy-investment steps where ATP is consumed to prepare glucose for further breakdown.

In the first step of glycolysis, ATP is used to phosphorylate glucose. This reaction is catalyzed by the enzyme hexokinase, and the product is glucose-6-phosphate. The reaction can be represented as:

ATP + {glucose}_{6} → {glucose}_{6} phosphate + ADP

In the third step of glycolysis, another ATP molecule is used. The enzyme phosphofructokinase catalyzes the phosphorylation of fructose-6-phosphate to form fructose-1,6-bisphosphate. This reaction can be represented as:

ATP + {fructose}_{6} phosphate → {fructose}_{1,6} bisphosphate + ADP

Recognize that the phosphorylation of glucose and fructose-6-phosphate by ATP makes these molecules more reactive and traps them inside the cell, as phosphorylated sugars cannot easily cross the cell membrane.

Summarize that ATP is used in the initial steps of glycolysis to invest energy, enabling the glucose molecule to be primed for subsequent breakdown and energy extraction in later steps of the pathway.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Adenosine Triphosphate (ATP)

ATP is the primary energy carrier in all living organisms. It consists of adenine, ribose, and three phosphate groups. The energy stored in the high-energy bonds between the phosphate groups is released when ATP is hydrolyzed to ADP and inorganic phosphate, making it essential for various cellular processes, including glycolysis.

Glycolysis

Glycolysis is a metabolic pathway that converts glucose into pyruvate, producing a small amount of ATP and NADH in the process. It occurs in the cytoplasm and consists of ten enzymatic reactions, divided into two phases: the energy investment phase and the energy payoff phase. The initial steps of glycolysis require ATP to phosphorylate glucose and its derivatives, facilitating subsequent reactions.

Phosphorylation

Phosphorylation is the addition of a phosphate group to a molecule, which often alters the molecule's activity or function. In glycolysis, the phosphorylation of glucose to glucose-6-phosphate is a crucial step that traps glucose in the cell and prepares it for further breakdown. This process is catalyzed by the enzyme hexokinase and is vital for the regulation of glucose metabolism.