No, catabolic reactions do not use energy to synthesize large molecules.

Here's why:

* Catabolic reactions break down large molecules into smaller ones. This process releases energy, making it an exergonic reaction. Think of it like dismantling a complex machine into its individual parts.

* Anabolic reactions use energy to build large molecules from smaller ones. This process requires energy input, making it an endergonic reaction. Think of it like assembling a complex machine from its parts.

In summary:

* Catabolism: Breaks down molecules, releases energy.

* Anabolism: Builds up molecules, requires energy.

Let me know if you have any other questions!