Phospholipids are used to construct plasma membranes. While there are many types of phospholipids in a plasma membrane, we are going to represent all of them in Petri Dish with a single generic phospholipid, phosphatidic acid. Phosphatidic acid can be used as a precursor to build other types of phospholipids, if necessary.
Phospholipid synthesis begins by diverting acetyl and glyceraldehyde-3-phosphate from the cellular respiration pathway. Acetyl is used to build malonyl in step 1, which is then used in steps 2-8 (known as the fatty acid cycle) to build palmitic acid with a 16-carbon chain. Glyceraldehyde-3-phosphate is converted into glycerol-3-phosphate in step 9, and two palmitic acids are attached to glycerol-3-phosphate to form a phospholipid in step 10.
| Step | Reactants | Products |
| 1 | C2H3O- (acetyl) + CO2 | C3H3O3- (malonyl) |
| 2 | C2H3O- (acetyl) + C3H3O3- (malonyl) | C4H7O- + CO2 + H2O |
| 3 | C4H7O- + C3H3O3- (malonyl) | C6H11O- + CO2 + H2O |
| 4 | C6H11O- + C3H3O3- (malonyl) | C8H15O- + CO2 + H2O |
| 5 | C8H15O- + C3H3O3- (malonyl) | C10H19O- + CO2 + H2O |
| 6 | C10H19O- + C3H3O3- (malonyl) | C12H23O- + CO2 + H2O |
| 7 | C12H23O- + C3H3O3- (malonyl) | C14H27O- + CO2 + H2O |
| 8 | C14H27O- + C3H3O3- (malonyl) | C16H31O- (palmitic acid) + CO2 + H2O |
| 9 | C3H5O6P2- (glyceraldehyde-3-phosphate) | C3H7O6P2- (glycerol-3-phosphate) |
| 10 | 2 C16H31O- (palmitic acid) + C3H7O6P2- (glycerol-3-phosphate) | phospholipid (phosphatidic acid) |
The metabolic pathway for building phosphatidic acid in Petri Dish has been simplified. Here is a more detailed version of the actual pathway:
| Step | Reactants | Products |
| 1 | acetyl-CoA + bicarbonate | malonyl-CoA |
| 2 | acetyl-CoA + ACP | acetyl-ACP + CoA |
| 3 | malonyl-CoA + ACP | malonyl-ACP + CoA |
| 4 | acetyl-ACP + malonyl-ACP | C4H5O2S-ACP + HS-ACP + CO2 |
| 5 | C4H5O2S-ACP + NADPH + H+ | C4H7O2S-ACP + NADP+ |
| 6 | C4H7O2S-ACP | C4H5OS-ACP + H2O |
| 7 | C4H5OS-ACP + NADPH + H+ | C4H7OS-ACP + NADP+ |
| Steps 4-7 are repeated to build the 16-carbon chain… | ||
| 28 | C14H27OS-ACP + malonyl-ACP | C16H29O2S-ACP + HS-ACP + CO2 |
| 29 | C16H29O2S-ACP + NADPH + H+ | C16H31O2S-ACP + NADP+ |
| 30 | C16H31O2S-ACP | C16H29OS-ACP + H2O |
| 31 | C16H29OS-ACP + NADPH + H+ | C16H31OS-ACP + NADP+ |
| 32 | C16H31OS-ACP + CoA | palmitoyl-CoA + ACP |
| 33 | glyceraldehyde-3-phosphate | dihydroxyacetone phosphate |
| 34 | dihydroxyacetone phosphate + NADH + H+ | glycerol-3-phosphate + NAD+ |
| 35 | glycerol-3-phosphate + palmitoyl-CoA | lysophosphatidic acid + CoASH |
| 36 | lysophosphatidic acid + palmitoyl-CoA | phosphatidic acid + CoASH |