Citric Acid Cycle Practice 3: Study with Video Lessons, Practice Problems & Examples

The citric acid cycle produces key intermediates like oxaloacetate, which is vital for anaplerotic reactions that replenish cycle components. Intermediates such as succinyl CoA contribute to the synthesis of porphyrins and hemes, while alpha-ketoglutarate aids in amino acid production. The isocitrate dehydrogenase reaction is crucial, as it generates NADH and releases CO₂, forming a double bond in the process. Understanding these metabolic pathways highlights their role in anabolic and catabolic reactions, emphasizing the interconnectedness of cellular metabolism.

Citric Acid Cycle Practice 3

The citric acid cycle intermediates are used to make many things, and amongst these are porphyrins. These must be replaced by the anaplerotic reactions that form oxaloacetate. Now, there are other things that the intermediates can make. For example, succinyl CoA, which makes porphyrins, can also be used to make hemes. Alpha-ketoglutarate is used to make amino acids. Oxaloacetate is also used to make oxalo acids and is used to make pyrimidine, so nucleic acids ultimately. It's important to know that the anaplerotic reactions are going to replace oxaloacetate, right? They are forming oxaloacetate to replace whatever intermediates need replacing.

Now, the isocitrate dehydrogenase reaction, I have drawn below. Here it is. I'll jump out of the image to give you a better look at it. So, that's what's going on, right? Basically, what's happening is we're losing CO₂. That's the CO₂ here. We are forming NADH from NAD⁺. Remember, this reaction is not like the pyruvate dehydrogenase reaction. Oh, and also we are forming a double bond between this oxygen and this carbon. See that over here.

Here’s what students ask on this topic:

What are the key intermediates of the citric acid cycle and their roles?

The key intermediates of the citric acid cycle include oxaloacetate, citrate, α-ketoglutarate, succinyl CoA, fumarate, and malate. Oxaloacetate is crucial for anaplerotic reactions that replenish cycle components. Citrate is involved in fatty acid synthesis. α-Ketoglutarate is essential for amino acid production. Succinyl CoA contributes to the synthesis of porphyrins and hemes. Fumarate and malate are involved in the regeneration of oxaloacetate. These intermediates play vital roles in both anabolic and catabolic pathways, highlighting the interconnectedness of cellular metabolism.

How does the isocitrate dehydrogenase reaction contribute to the citric acid cycle?

The isocitrate dehydrogenase reaction is a crucial step in the citric acid cycle. It catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate, producing NADH and releasing CO₂. The reaction can be summarized as:

${\mathrm{isocitrate}}_{}+{\mathrm{NAD}}_{}+H_{}\to {\alpha }_{}-{\mathrm{ketoglutarate}}_{}+{\mathrm{CO}}_{}2+{\mathrm{NADH}}_{}$

This reaction is important for energy production and the regulation of the cycle, as NADH is a key electron carrier in cellular respiration.

What are anaplerotic reactions and why are they important in the citric acid cycle?

Anaplerotic reactions are metabolic pathways that replenish intermediates of the citric acid cycle. These reactions are crucial because intermediates are often diverted for biosynthetic processes, such as amino acid and nucleotide synthesis. For example, pyruvate carboxylase converts pyruvate to oxaloacetate, ensuring a continuous supply of this key intermediate. The importance of anaplerotic reactions lies in maintaining the cycle's functionality, which is essential for energy production and various biosynthetic pathways.

How does succinyl CoA contribute to the synthesis of hemes and porphyrins?

Succinyl CoA is a key intermediate in the citric acid cycle that contributes to the synthesis of hemes and porphyrins. It combines with glycine to form δ-aminolevulinic acid (ALA), the first step in the biosynthesis of porphyrins. These porphyrins are then converted into hemes, which are essential components of hemoglobin, myoglobin, and various cytochromes. This pathway highlights the interconnectedness of the citric acid cycle with other vital biochemical processes.

What role does α-ketoglutarate play in amino acid production?

α-Ketoglutarate is a crucial intermediate in the citric acid cycle that plays a significant role in amino acid production. It serves as a precursor for the synthesis of glutamate through the action of glutamate dehydrogenase. Glutamate can then be used to synthesize other amino acids via transamination reactions. This process is vital for protein synthesis and various metabolic functions, demonstrating the importance of α-ketoglutarate in cellular metabolism.