Question

Mouse embryonic stem cells divide extremely rapidly, about once every 5 hours. These cells require large amounts of threonine in their medium. Explain how threonine catabolism (Fig. 21-14) helps meet the cells’ energy needs and their high rate of DNA synthesis.

Short answer

Acetyl-CoA and glycine.

Step-by-step solution

Role of α-amino--ketobutyrate.

Threonine dehydrogenaseproduces $\alpha$-amino--ketobutyrate,which is the most common form of threonine breakdown in mammals. $\alpha$-amino-$\beta$-ketobutyrate lyase converts $\alpha$-amino-$\beta$-ketobutyrate to acetyl-CoA.Serine hydroxymethyltransferase or the $\alpha$-amino-$\beta$-ketobutyrate intermediate can also convert threonine to glycine.

Acetyl-CoAhas the capacity to penetrate the citric acid cycle as well as produce a lot of ATPs.

Use of Glycine.

Glycineis used in the glycine cleavage pathwayto make ${\text{N}}^{\text{5}}{\text{,N}}^{\text{10}}$-methylene-THF. In the synthesis of thymidylate, an important precursor for DNA biosynthesis,${\text{N}}^{\text{5}}{\text{,N}}^{\text{10}}$-methylene-THF acts as a methyl group donor.

Threonine catabolism.

Threonine catabolism produces acetyl-CoA and glycine, which assist cells satisfy their energy needs and maintain their significant increase of DNA synthesis. Acetyl-CoA can go on to make ATP in the citric acid cycle, whereas breakdown of glycine yields THF cofactor, a methyl group donor for thymidylate.