Microbial Metabolism

Catabolic and Anabolic Reactions

The sum of all chemical reactions within a living organism is known as metabolism.

Metabolic pathways are a series of chemical reactions in which the product of one reaction is the substrate for the next reaction.  The chemical reactions are catalyzed by enzymes, so the metabolic pathways present in an organism depend on the enzymes present in the organism.  The enzymes present in an organism depend on the genes present in the organism. 

Catabolism refers to chemical reactions that result in the breakdown of more complex organic molecules into simpler substances.

Catabolic reactions usually release energy that is used to drive chemical reactions.

Anabolism refers to chemical reactions in which simpler substances are combined to form more complex molecules.  Anabolic reactions usually require energy.

Anabolic reactions build new molecules and/or store energy.

The energy of catabolic reactions is used to drive anabolic reactions.

The energy for chemical reactions is stored in ATP.

Often when I ask students "What is ATP" the answer they give is "Energy".  This may be a shorthand answer but what I am looking for is "Adenosine triphosphate, a molecule that contains three phosphates held together by high energy bonds.  When the third phosphate is cleaved, leaving adenosine diphosphate (ADP), energy is released to drive anabolic reactions.  Energy is required to add a third phosphate to ADP to form ATP; the energy comes from catabolic reactions and is stored in the newly formed bond."  Or, my shorthand: "The rechargeable battery of the cell".