A transamination reaction with glutamate forms 3-phosphoserine and removal of the phosphate yields serine. Glycine is generated by removal of the methyl group from serine. Figure 7 - Synthesis of Serine and Glycine. Note that this pathway actually yields energy and carbon for other uses. The intermediates are so similar that common enzymes catalyze four steps of each pathway.
Isoleucine synthesis begins with threonine, which is deaminated to a -ketobutyrate.
Figure 8 - Synthesis of valine and isoleucine. Leucine biosynthesis starts of with the last intermediate in the valine synthesis, a -ketoisovalerate. In the first step Acetyl-CoA is used to add an acetyl group to the molecule. In the final step, the amine from glutamate is added to a -ketoisocaproate to form leucine. Figure 9 - Synthesis of leucine.