Question

The conversion of ATP to cyclic AMP and inorganic phosphate is most likely catalyzed by which class of enzyme? (A) Ligase (B) Hydrolase (C) Lyase (D) Transferase

Short answer

The reaction is most likely catalyzed by a Lyase (C).

Step-by-step solution

- Understand the Reaction

The given reaction is the conversion of ATP to cyclic AMP and inorganic phosphate. This specific reaction involves breaking a phosphoanhydride bond in ATP.

- Identify the Enzyme Classes

Review the types of enzyme classes: Ligases catalyze the joining of two molecules with ATP. Hydrolases catalyze hydrolysis reactions. Lyases catalyze the breaking of various chemical bonds without water. Transferases transfer functional groups between molecules.

- Match Reaction to Enzyme Class

Since the reaction involves breaking a bond without adding water, it is not catalyzed by a Hydrolase. Ligase and Transferase do not fit this reaction because there is no joining of molecules or transferring of groups. Thus, the reaction is most likely catalyzed by a Lyase, which can break chemical bonds without the involvement of water.

- Verify with Examples

As an example, adenylate cyclase, which catalyzes the conversion of ATP to cyclic AMP and phosphate, is a known Lyase.

Key concepts

Lyases

Lyases are a crucial class of enzymes in biochemistry. These enzymes catalyze the breaking of various chemical bonds by means other than hydrolysis (breaking with water) or oxidation. They are unique because they can break bonds to form a new double bond or a new ring structure, or add groups to double bonds.
For the MCAT, it's essential to understand that Lyases often participate in reactions where substrates are split without the use of water. For instance, adenylate cyclase, which converts ATP (adenosine triphosphate) to cyclic AMP (cAMP) and inorganic phosphate, is a classic example of a Lyase. Remember, the ATP conversion mentioned here involves breaking a phosphoanhydride bond, which fits the definition of a Lyase's action.

ATP conversion

ATP conversion is a fundamental biochemical process. ATP, often called the cell's energy currency, is used in various cellular processes due to its high-energy phosphate bonds. In the specific reaction of converting ATP to cyclic AMP and inorganic phosphate, the ATP molecule is broken down.
This conversion is significant as it forms cyclic AMP (cAMP), a crucial secondary messenger in many biological processes. The enzyme responsible for this conversion, adenylate cyclase, strips a phosphate group from ATP to create cAMP. This reaction does not involve water, distinguishing it from hydrolytic actions and placing it under the action of Lyases.

cyclic AMP

Cyclic AMP, or cAMP, is a versatile and vital secondary messenger in cells. It is derived from ATP through a reaction catalyzed by the enzyme adenylate cyclase.
cAMP plays a critical role in many biological processes, including the regulation of glycogen, sugar, and lipid metabolism. It acts by activating protein kinase A (PKA), which phosphorylates various target proteins, leading to altered cellular activity.
Understanding the importance of cAMP in signal transduction and how it bridges extracellular signals to intracellular responses is crucial. For MCAT, remember that the formation of cAMP from ATP is a reaction typically facilitated by Lyases, reflecting the need to recognize enzyme actions and their specificity.

biochemistry reactions

Biochemistry reactions encompass all chemical processes occurring within living organisms. These reactions are catalyzed by enzymes, which speed up the process and ensure proper cellular function.
In the context of the given problem, understanding different classes of enzymes and the specific reactions they catalyze is necessary. For example, recognizing that Lyases, such as adenylate cyclase, can break down ATP to form cAMP is a key takeaway.

• Ligases: Join two molecules together using ATP.
• Hydrolases: Use water to break bonds.
• Lyases: Break bonds without water or oxidation.
• Transferases: Transfer functional groups between molecules.

Mastering these concepts will prepare you well for enzyme-related questions on the MCAT.

MCAT prep

Preparing for the MCAT involves thorough understanding and memorization of core concepts in biochemistry, including enzyme classification and function. To excel in enzyme-related questions:

• Know the main classes of enzymes and their functions.
• Understand specific reactions catalyzed by enzymes, such as ATP conversion to cAMP by Lyases.
• Familiarize yourself with secondary messengers like cAMP and their role in cell signaling.
• Practice with multiple-choice questions to identify common pitfalls and mastery through repetition.

Regular review and practice will reinforce these concepts, ensuring you are well-prepared for the exam's biochemistry section.