Q. 18.37 - An Introduction to General, Organic, and Biological Chemistry

Question

Identify the reaction(s) of the citric acid cycle that involve(s)

a. oxidation and decarboxylation

b. dehydration

c. reduction of ${\mathrm{NAD}}^{+}$

Step-by-Step Solution

Answer

(a) The reactions $3, 4$ involves oxidation and decarboxylation

(b) The reaction $6$ involves dehydration

(c) The reactions $3, 4, 8$ involves reduction of data-custom-editor="chemistry" ${\mathrm{NAD}}^{+}$

Part (a) Step 1: Given information

We need to find the reaction that involves oxidation and decarboxylation.

Part (a) Step 2: Explanation

We know that 

• The carboxylate group was converted into a carbon dioxide molecule in Reaction $3$ of the citric cycle, yielding $\mathrm{\alpha }$-ketoglutarate. As the carboxyl group is removed, decarboxylation produces carbon dioxide molecules; thus, this is a decarboxylation reaction. Also notice that the oxidation reaction produced hydrogen ions, which reduced ${\mathrm{NAD}}^{+}$ to $\mathrm{NADH}$ in the same step.
• In Reaction $4$, ketoglutarate is decarboxylated, resulting in a four-carbon group that joins $\mathrm{CoA}$ to generate succinyl-$\mathrm{CoA}$. The oxidation reaction created hydrogen ions, which converted ${\mathrm{NAD}}^{+}$ to $\mathrm{NADH}$ in the same way that Reaction $3$ did.

Part (b) Step 1: Given information

We need to find the reaction that involve dehydration

Part (b) Step 2: Explanation

We know that

Two hydrogen atoms were removed in Reaction $6$ to form fumarate, resulting in dehydrogenation, as indicated in the diagram below.

Therefore, The reaction $6$ involves dehydration

Part (c) Step 1: Given information

We need to find the reaction  that involves reduction of ${\mathrm{NAD}}^{+}$

Part (c) Step 2: Explanation

We know that

In Reaction $3$, the hydrogen ions created by the oxidation of the proteins have reduced data-custom-editor="chemistry" $\mathrm{NAD}$ to data-custom-editor="chemistry" $\mathrm{NADH}$. The same is true for Reactions $4$ and $8$.

Therefore, 

The reactions $3, 4, 8$ involves reduction of $NA{D}^{+}$