Chapter $17\mathrm{.}2$

The Urea cycle: Chapter $17$

Before the urea cycle can occur, $N{H}_3$ must be released from the glutamate$/$glutamine and subsequently trapped in the form of carbamoyl phosphate. This is actually considered step $l$ even though it is not part of the cycle.

a$.$ Write the net equation for the formation of carbamoyl phosphate from $HC{O}_3^{1-}$ and $N{H}_3.$ Be sure to include other major reactants and products $($e$.$g$.$ ATP$).$

$HC{O}_3^{2-}+$ATP$+N{H}_{3}longrightarrow{P}_i+$ADP$+$ Carbamouiphosphate

b$.$ Draw the mechanism for the formation of carbamoyl phosphate, starting from ATP and bicarbonate $(HC{O}_3^{2-}).$ The reaction occurs in $3$ discrete steps. You do not need to show the reaction intermediates but DO need to show the movement of electrons $($arrows$).$

c$.$ Answer the following questions.

i$)$ What intermediate would form in steps $1$ and $3$: pentavalent

ii$)$ What intermediate would form in step $2$: $q,$ endiol

iii$)$ What does the role$($s$)$ of the phosphate group serve?