The carbon skeletons of specific amino acids cannot be used to replenish which of the following species associated with the citric acid cycle?
a. pyruvate
b. citrate
c. fumarate
d. succinyl CoA
e. all of these can be used
Question 2
Which of the following is not an intermediate in the urea cycle?
a. arginine
b. citrulline
c. ornithine
d. lysine