Problem 90 - Objective Biology for NEET

Question

In Kreb's cycle, the FAD precipitates as electron acceptor during the conversion of (a) Succinyl CoA to succinic acid (b) \(\alpha\) -ketoglutarate to succinyl \(\mathrm{CoA}\) (c) Fumaric acid to maleic acid (d) Succinic acid to fumaric acid

Step-by-Step Solution

Answer

(d) Succinic acid to fumaric acid is the correct option. In this conversion, FAD acts as an electron acceptor, turning into FADH2.

Step 1: Understanding the Kreb's Cycle

The Kreb's cycle, also known as the citric acid cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins into carbon dioxide and potential energy in the form of ATP.

Step 2: Identifying the Role of FAD

FAD is a molecule that's crucial for metabolism. It accepts two hydrogen atoms, becoming FADH2. In the context of the Kreb's cycle, FAD is responsible for the oxidation of succinic acid (Succinate).

Step 3: Matching the Provided Options

Going through the provided options, the conversion during which FAD acts as an electron acceptor is identified as the conversion of succinic acid to fumaric acid.

Key Concepts

FAD as electron acceptor

In the Krebs Cycle, FAD plays a critical role as an electron acceptor. But what does this mean?
In simpler terms, FAD (Flavin Adenine Dinucleotide) is a molecule that helps transfer energy within cells.
It is essential during metabolism because it picks up electrons and hydrogen atoms, transforming into FADH2.
This change is vital as it helps facilitate further reactions that produce ATP, the energy currency of the cell.

• Why is FAD important?
  FAD is involved in several reactions in the Krebs Cycle and is pivotal when electrons need a home to go to, specifically from succinic acid during its conversion to fumaric acid.
  FADH2, the reduced form of FAD, subsequently transfers its electrons to the electron transport chain, creating ATP.
  

Thus, FAD is not only an acceptor but also an essential participant in our body's energy production.
Understanding FAD's role highlights the interconnected nature of cellular respiration and how our bodies maximize energy extraction from nutrients.

Oxidation of succinic acid

When we talk about the oxidation of succinic acid in the Krebs Cycle, we focus on a very specific reaction.
This reaction represents the fourth step of the Krebs Cycle, and it is critical for energy production.

• What happens during this step?
  Succinic acid undergoes oxidation, meaning it loses electrons.
  FAD captures these electrons and hydrogen atoms, changing the succinic acid into fumaric acid.
  This process turns FAD into FADH2.
  
• Significance of this reaction
  This oxidation step is crucial as it directly ties into the electron transport chain, where most of the ATP is produced.
  By capturing these electrons, FADH2 contributes to a greater yield of 2 ATP molecules once it donates these energetic electrons.
  

This reaction underscores the importance of oxidative reactions in energy conversion and the central role FAD plays as a carrier of energy-rich electrons.

Conversion of succinic acid to fumaric acid

The conversion of succinic acid to fumaric acid is a key step within the Krebs Cycle.
This transformation is facilitated by the enzyme succinate dehydrogenase.

• This enzymatic process
  The enzyme catalyzes the removal of two hydrogen atoms from succinic acid.
  These atoms are transferred to FAD, which gets reduced to FADH2.
  This marks the conversion of succinic acid, or succinate, to fumaric acid, or fumarate.
  
• Role in the Krebs Cycle
  This conversion is pivotal as it's the only step in the Krebs Cycle that takes place on the inner mitochondrial membrane.
  It links directly to the electron transport chain, emphasizing the cycle's integration with other metabolic processes. This efficiency illustrates how fats, proteins, and carbohydrates are all interconnected in energy production.
  

Overall, the conversion of succinic acid to fumaric acid demonstrates the efficiency and interconnectivity of biochemical pathways in energy production, highlighting the precision of metabolic processes within cells.