Question

Reflect and Apply 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

Statements: (a) False, (b) False, (c) True.

Step-by-step solution

Understanding Coenzymes (Part a)

Examine the first statement: 'All coenzymes are electron-transfer agents.' Coenzymes are organic molecules that assist enzymes in catalyzing reactions. Some coenzymes, such as NAD+ and FAD, are involved in electron transfer, but many others, like coenzyme A, function in different roles such as group transfer. Hence, the statement is not true because not all coenzymes participate in electron transfer.

Investigating Coenzyme Composition (Part b)

Analyze the second statement: 'Coenzymes do not contain phosphorus or sulfur.' Coenzymes are diverse in their structures; some contain phosphorus (e.g., NADP+ contains phosphorylated groups) and others contain sulfur (e.g., coenzyme A contains both sulfur and phosphorus). Therefore, the statement is false as coenzymes can and do contain these elements.

Evaluating Energy Storage (Part c)

Consider the third statement: 'Generating ATP is a way of storing energy.' ATP (adenosine triphosphate) is a primary energy carrier in cells. It stores energy in its high-energy phosphate bonds, which can be hydrolyzed to release energy for cellular processes. Thus, the statement is true because generating ATP indeed stores energy.

Key concepts

Electron-Transfer Agents

In biological systems, electron-transfer agents play a crucial role in various metabolic processes. These agents are involved in oxidation-reduction (redox) reactions. In these reactions, electrons are transferred from one molecule (the reductant) to another molecule (the oxidant). Key electron-transfer agents in cells include NAD+ (Nicotinamide adenine dinucleotide) and FAD (Flavin adenine dinucleotide). These coenzymes assist enzymes in transferring electrons during cellular respiration. This transfer of electrons helps in the production of ATP, the energy currency of the cell. Notably, not all coenzymes function as electron-transfer agents. While some participate directly in electron transfer, others, like coenzyme A, play different roles such as group transfer.

Enzyme Catalysis

Enzyme catalysis is a process that increases the rate of a biochemical reaction by lowering the activation energy. Enzymes are proteins that act as catalysts to speed up reactions without being consumed. Coenzymes often assist enzymes in this process by acting as carriers for various chemical groups or electrons. The interaction between an enzyme and its coenzyme is highly specific, contributing to the precise regulation of metabolic pathways. For example, the coenzyme A (CoA) is vital in the synthesis and oxidation of fatty acids. CoA contains both sulfur and phosphorus, showcasing the diversity in coenzyme composition. This diversity allows coenzymes to participate in a wide range of biochemical reactions.

ATP Energy Storage

ATP, or adenosine triphosphate, is often referred to as the 'energy currency' of the cell. It stores energy in the form of high-energy phosphate bonds. These bonds can be hydrolyzed (broken down) to release energy, which can then be used to power various cellular processes such as muscle contraction, protein synthesis, and cell division. The generation of ATP, primarily through cellular respiration, is a critical way for cells to store energy efficiently. The process involves converting the energy from nutrients into a usable form. During cellular respiration, glucose is oxidized, and the energy released is used to synthesize ATP from ADP (adenosine diphosphate) and inorganic phosphate. This process underscores the role of ATP in energy storage and its importance in maintaining cellular functions.