Question

Which of the following statements are true? For each, explain why or why not. (a) All coenzymes are electron-transfer agents. (b) Coenzymes do not contain phosphorus or sulfur. (c) Generating ATP is a way of storing energy.

Short answer

Only statement (c) is true.

Step-by-step solution

Analyze Statement (a)

Statement (a) claims that all coenzymes are electron-transfer agents. Coenzymes have various roles in biological processes such as acting as carriers of electrons, specific atoms or functional groups, and participating in enzyme-catalyzed reactions. Examples include NAD+ (which is an electron-transfer agent) and coenzyme A (which carries acyl groups). Not all coenzymes participate in electron transfer.

Evaluate Statement (a)

Since not all coenzymes function as electron-transfer agents, this statement is false.

Analyze Statement (b)

Statement (b) claims that coenzymes do not contain phosphorus or sulfur. Many coenzymes, such as NAD+ (which contains phosphorus in the form of a phosphate group) and Coenzyme A (which contains sulfur in the form of a thiol group), do indeed contain these elements.

Evaluate Statement (b)

Given that some coenzymes contain phosphorus or sulfur, this statement is false.

Analyze Statement (c)

Statement (c) claims that generating ATP is a way of storing energy. ATP (adenosine triphosphate) serves as a primary energy carrier in cells. The energy stored in its high-energy phosphate bonds is used to drive various biological processes.

Evaluate Statement (c)

Since ATP is indeed a way that cells store and utilize energy, this statement is true.

Key concepts

electron transfer

Electron transfer is a fundamental process in biochemistry where electrons move from one molecule to another. This movement is essential in various biochemical reactions, specifically those involved in cellular respiration and photosynthesis.
Coenzymes, like NAD+ (nicotinamide adenine dinucleotide), often facilitate electron transfer. NAD+ accepts electrons during reactions and turns into NADH, which then carries the electrons to other reactions. But keep in mind, not all coenzymes are involved in electron transfer. For instance, coenzyme A mainly carries acyl groups, making it crucial in metabolism but not in electron transfer.

Understanding electron transfer is vital since it drives the production of ATP, the energy currency of the cell.

phosphorus

Phosphorus is a critical element in biology, found in nucleic acids (DNA and RNA) and in molecules like ATP. In coenzymes, phosphorus often appears in the form of phosphate groups. For example, NAD+ contains phosphorus as part of its structure.
These phosphate groups are involved in transferring energy. When ATP loses a phosphate group to become ADP (adenosine diphosphate), this process releases energy that the cell can use. Hence, coenzymes with phosphorus are crucial for energy transfer and storage in cells, demonstrating the importance of this element in biological systems.

sulfur

Sulfur is another essential element in biology, appearing in amino acids like cysteine and methionine, and in coenzymes like coenzyme A. Coenzyme A includes a sulfur-containing thiol group, which is necessary for its function in transferring acyl groups.
This thiol group can form high-energy bonds with acyl groups in metabolic reactions, such as the Krebs cycle where acetyl-CoA plays a central role. Thus, the sulfur element in coenzymes is key to various metabolic pathways, showing its significance in bioenergetics and metabolism.

ATP

ATP (adenosine triphosphate) is the main energy currency used by cells. It stores energy in the form of high-energy phosphate bonds. When the body needs energy, ATP is broken down into ADP (adenosine diphosphate) and an inorganic phosphate; this process releases energy.
Cells generate ATP through cellular respiration, a series of reactions that take place in mitochondria, or through photosynthesis in plants. ATP is essential for many cellular processes, including muscle contraction, nerve impulse propagation, and chemical synthesis. Therefore, generating ATP is indeed a way of storing and utilizing energy efficiently.

energy storage

Energy storage in biological systems is crucial for maintaining cellular functions. The primary molecule for energy storage and transfer is ATP. Cells store energy in the form of ATP's high-energy phosphate bonds. When these bonds break, energy is released to power various cellular activities.
Besides ATP, cells also store energy in other forms, such as glycogen in animals and starch in plants. These storage forms can be converted back into ATP when energy is needed. Effective energy storage and release mechanisms ensure that cells function smoothly, supporting activities like growth, repair, and maintenance.
Overall, understanding how cells store and utilize energy can provide insights into their efficient functioning and how energy balance is maintained.