Question

4. THFA is an importantcontributor to the synthesis of both purines and a specificpyrimidine. Which pyrimidine? Why does ablock in the enzyme dihydrofolate reductase (DHFR) have negativeconsequences on nucleotide biosynthesis? What othernegative consequences does this have: i.e. what other pathwaysmight be influenced? Why?

5. What distinguishes thecarbamoyl phosphate synthetase used for the urea cycle (CPS I) fromthat used for de novo pyrimidine biosynthesis (CPS II)? This shouldinclude the following characteristics: pathway, cellular location,nitrogen source, and regulation.

6. What is meant by substratechanneling? How is CPS II an example of anenzyme that utilizes this?