This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urea cycle, Subject name: Biochemistry
The conversion of glutamate to glutamine is catalysed by a 
Select and explain. 
A. Lyase, B. Ligase, C. Transferase, D. Oxidoreductase
B: Ligase
Answer: B: Ligase 
Explanation: Glutamine is a nutritionally non-essential amino acid It is synthesised from glutamate Free ammonia is ligated to glutamate (that is why ligase) with the use of energy provided by ATP hydrolysis. The enzyme is glutamine synthetase (Synthetase requires ATP while synthase does not require ATP).