Q. 18.38 - An Introduction to General, Organic, and Biological Chemistry

Question

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

a. reduction of $\mathrm{FAD}$

b. direct phosphate transfer 

c. hydration

Step-by-Step Solution

Answer

(a) The reaction $6$ involve reduction of $\mathrm{FAD}$

(b) The reaction $5$ involve direct phosphate transfer

(c) The reaction $7$ involve hydration

Part (a) Step 1: Given information

We need to find the reaction(s) of the citric acid cycle that involve(s) reduction of $\mathrm{FAD}$

Part (a) Step 2: Explnation

We know that

In Reaction $6$, two hydrogen ions are removed from the parent chain as succinate is dehydrogenated. As demonstrated below, these hydrogen ions convert $\mathrm{FAD}$ to

Therefore,

The reaction $6$ involve reduction of $\mathrm{FAD}$

Part (b) Step 1: Given information

We need to find the reaction that involves direct phosphate transfer

Part (b) Step 2: Explanation

We know that

After the hydrolysis of succinyl-$\mathrm{CoA}$, succinate and $\mathrm{CoA}$ were generated in Reaction $5$. The reaction's energy was utilized to add a phosphate group to guanine diphosphate ($\mathrm{GDP}$), a phosphate acceptor, resulting in guanine triphosphate ($\mathrm{GTP}$) and the release of energy. The energy released from $\mathrm{GTP}$ is used to add a phosphate group to adenosine diphosphate ($\mathrm{ADP}$) to make adenosine triphosphate ($\mathrm{ATP}$).

Therefore, 

The reaction $5$ involves direct phosphate transfer 

Part (c) Step 1: Given information

We need to find the reaction that involves hydration

Part (c) Step 2: Explanation

We know that

A water molecule was introduced to Reaction $7$ to react with fumarate, dissolving its double bond and generating malate.

Therefore, 

The reaction $7$ involve hydration.