Problem 5 - Campbell Biology

Question

What is the oxidizing agent in the following reaction? $$\text { Pyruvate }+\mathrm{NADH}+\mathrm{H}^{+} \rightarrow \text { Lactate }+\mathrm{NAD}^{+}$$ (A) oxygen (B) NADH (C) lactate (D) pyruvate

Step-by-Step Solution

Answer

The oxidizing agent is pyruvate.

Step 1: Review the Concept of Oxidizing Agent

An oxidizing agent is a substance that gains electrons in a chemical reaction. This means it gets reduced in the process, while the other substance gets oxidized.

Step 2: Identify the Substances on Both Sides of the Reaction

In the given reaction, the substances involved are pyruvate, NADH, H+, lactate, and NAD+.

Step 3: Determine the Changes in Oxidation States

NADH is converted to NAD+, indicating that NADH is losing electrons (being oxidized). Conversely, to balance the equation, pyruvate must be gaining electrons (being reduced) to form lactate.

Step 4: Identify the Oxidizing Agent

Since pyruvate is gaining electrons, it is being reduced. Therefore, pyruvate is the oxidizing agent in this reaction.

Step 5: Select the Correct Answer

The correct answer is (D) pyruvate.

Key Concepts

Redox Reactions

Redox reactions are chemical reactions where oxidation and reduction occur simultaneously. Oxidation refers to the loss of electrons, while reduction refers to the gain of electrons. One substance gets oxidized by losing electrons, and another substance gets reduced by gaining those electrons.
These reactions are essential to many biochemical processes, such as cellular respiration and photosynthesis.
During redox reactions, the substance that donates electrons is called the reducing agent, and the one that accepts electrons is the oxidizing agent. Understanding these agents helps in identifying the changes happening in reactions, such as when pyruvate acts as the oxidizing agent in the given reaction.

Electron Transfer

Electron transfer is a core part of redox reactions. It involves the movement of electrons from one molecule to another.
The molecule that loses electrons undergoes oxidation, and its oxidation state increases. Conversely, the molecule that gains electrons undergoes reduction, and its oxidation state decreases.
This transfer of electrons is vital in energy production, notably in the mitochondrial electron transport chain during cellular respiration.

• Example: In the reaction between pyruvate and NADH, NADH loses electrons and is oxidized to NAD+.
• Pyruvate gains these electrons and is reduced to lactate.

Recognizing how electron transfer works in these reactions is crucial in identifying the oxidizing and reducing agents.

Oxidation States

Oxidation states indicate the degree of oxidation of an atom within a molecule. They help in understanding the electron transfer during redox reactions.
A higher oxidation state means the atom has lost electrons, whereas a lower oxidation state means it has gained electrons.
In biochemical reactions, oxidation states help in identifying which molecules are oxidized and which are reduced.
For example, in the reaction provided:

• NADH is oxidized to NAD+ (loses electrons).
• Pyruvate is reduced to lactate (gains electrons).

By knowing the changes in oxidation states, we can determine the oxidizing agent. In this case, pyruvate gains electrons and is reduced, making it the oxidizing agent in the reaction.