# Catabolism --- **Catabolism** is the name of the [[metabolism|metabolic pathways]] that break down molecules to smaller pieces. We can then use those pieces to rebuild into the macromolecules that we do need. These reactions *require* often harvest stored chemical energy to produce [[adenosine triphosphate]]. ## Carbohydrates The main pathway for breaking down carbohydrates is [[glycolysis]]. The [[pentose phosphate pathway]] is an alternate pathway. ## Proteins Proteins can be broken down to amino acids through a process called **proteolysis**, and, as the body does not really "store" extra proteins for fuel, this process happens during digestion, or during standard protein repair. Those "extra" amino acids can then enter glycolysis or become a different, non-essential amino acid. In the event that the body needs to use it's own protein to burn for fuel or as fodder for other amino acids, it can take individual amino acids and [[deamination|deaminate]] them to ultimately form [[acetyl CoA]] to power the citric acid cycle or to be [[transamination|transaminated]] into other amino acids. ## Lipids The breakdown of lipids is called [[lipolysis]]. To be broken down, first the lipid has to be split into it's two parts. Then the glycerol can be converted to an intermediate product of [[glycolysis]], and the fatty acid can be broken down to create [[acetyl CoA]]. ___