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. Statements (a) and (b) are false.

Step-by-step solution

Evaluating Statement (a)

Analyze if all coenzymes are electron-transfer agents. Consider the functions of various coenzymes. Some examples, like coenzyme A, are involved in carrying acyl groups rather than electrons. Hence, not all coenzymes are electron-transfer agents.

Evaluating Statement (b)

Review the elemental composition of coenzymes. Many coenzymes like NADP (Nicotinamide adenine dinucleotide phosphate) and Coenzyme A contain either phosphorus or sulfur. Therefore, the statement that coenzymes do not contain phosphorus or sulfur is incorrect.

Evaluating Statement (c)

Consider the role of ATP in cellular processes. ATP (adenosine triphosphate) stores energy in its high-energy phosphate bonds, which can be utilized by the cell to perform various functions. Thus, generating ATP is indeed a way of storing energy.

Key concepts

Electron-transfer Agents

Coenzymes play a pivotal role in the biochemical processes within our cells. One of the significant functions of certain coenzymes is to act as electron-transfer agents. However, it's crucial to understand that not all coenzymes perform this function. For instance, coenzyme A is not primarily involved in electron transfer but rather in transferring acyl groups.

Electron transfer is a core part of cellular respiration and photosynthesis, where specific coenzymes like NADH (Nicotinamide adenine dinucleotide) and FADH2 (Flavin adenine dinucleotide) shuttle electrons between different molecules in the cell. This process helps in converting food into usable energy.

- **NADH and FADH2:** These are quintessential electron-transfer agents involved in cellular respiration.
- **Coenzyme A:** It mainly carries acyl groups, showing that not all coenzymes transfer electrons.

Elemental Composition of Coenzymes

Coenzymes are organic non-protein molecules that bind with enzymes to catalyze reactions in the body. They contain various elements, including carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

• **NADP (Nicotinamide adenine dinucleotide phosphate):** Contains both nitrogen from the nicotinamide and phosphorus as part of the phosphate groups.
• **Coenzyme A:** Includes sulfur in its molecular structure.

So, the idea that coenzymes do not contain phosphorus or sulfur is incorrect. In fact, many vital coenzymes incorporate these elements to carry out their functions. This elemental diversity allows them to participate in various biochemical processes, from energy production to the synthesis of essential biomolecules.

ATP Energy Storage

ATP, or adenosine triphosphate, is the energy currency of the cell. It stores and supplies energy necessary for many cellular processes. The energy is stored in the high-energy phosphate bonds and can be quickly released when required.

When the cell needs energy, it breaks the bond of one of the three phosphate groups in ATP, turning it into ADP (adenosine diphosphate). This process releases energy, which can be used for cellular activities.

• **High-energy phosphate bonds:** The bonds between the phosphate groups in ATP store significant amounts of energy.
• **ATP to ADP conversion:** This conversion releases energy that the cell can use for various functions, such as muscle contraction, nerve impulse propagation, and chemical synthesis.

Therefore, generating ATP is indeed a way of storing energy, making it a critical molecule for life.