Problem 83 - Objective Biology for NEET

Question

Which of the following is the correct sequence in Kreb's cycle? (a) Isocitric acid \(\rightarrow\) Oxalosuccinic acid \(\rightarrow \alpha\) -ketoglutaric acid (b) Oxalosuccinic acid \(\rightarrow\) Isocitric acid \(\rightarrow \alpha\) -ketoglutaric acid (c) \(\alpha\) -ketoglutaric acid \(\rightarrow\) Isocitric acid \(\rightarrow\) Oxalosuccinic acid (d) Isocitric acid \(\rightarrow \alpha\) -ketoglutaric acid \(\rightarrow\) Oxalosuccinic acid

Step-by-Step Solution

Answer

The correct sequence in Kreb's cycle is (a) Isocitric acid \(\rightarrow\) Oxalosuccinic acid \(\rightarrow \alpha\)-ketoglutaric acid.

Step 1: Recall the sequence in Kreb's Cycle

Kreb's Cycle begins with Citric Acid or Isocitric acid. This acid goes through multiple transformations becoming diverse compounds. The sequence should be: Isocitric acid (or Citric acid) \(\rightarrow\) Oxalosuccinic acid (or Oxalocetate) \(\rightarrow\) \(\alpha\)-ketoglutaric acid.

Step 2: Compare the options given with the correct sequence

In our exercise, the option that fits the sequence is (a) Isocitric acid \(\rightarrow\) Oxalosuccinic acid \(\rightarrow \alpha\)-ketoglutaric acid.

Step 3: Select the correct option

Therefore, the correct sequence in Kreb's cycle is given by answer (a).

Key Concepts

Isocitric Acid

Isocitric acid is one of the key intermediates in the Kreb's Cycle, which is also known as the Citric Acid Cycle. This cycle is a crucial component of cellular respiration, the process by which our cells generate energy.
The cycle begins when acetyl-CoA combines with oxaloacetate to form citric acid. Through a series of enzymatic transformations, citric acid is eventually converted into isocitric acid. This conversion is catalyzed by the enzyme aconitase.
Isocitric acid plays a crucial role in releasing energy stored in nutrients as it is further processed into subsequent metabolites. Understanding the transformation from isocitric acid to the next compound is important for grasping how energy production is regulated in cells.

Oxalosuccinic Acid

Oxalosuccinic acid is another significant intermediate in the Kreb's Cycle, formed from isocitric acid. It is crucial as it undergoes a rapid decarboxylation to produce \( \alpha \)-ketoglutaric acid.
This transition is facilitated by the enzyme isocitrate dehydrogenase, converting NAD+ (Nicotinamide adenine dinucleotide) into its reduced form, NADH, while releasing a molecule of carbon dioxide. This step is essential because:

• It contributes to reducing power in the form of NADH, vital for subsequent electron transport chain steps.
• It represents a decarboxylation reaction, one of the cycle's profound chemical transformations.

Through the efficient working of enzymes, oxalosuccinic acid ensures energy currency and intermediates are maintained for the cycle's progression.

Alpha-Ketoglutaric Acid

\( \alpha \)-Ketoglutaric acid, formed from oxalosuccinic acid, is a pivotal intermediate in the Kreb's Cycle. It plays a dual role in energy metabolism and biosynthesis.
After formation from oxalosuccinic acid, \( \alpha \)-ketoglutaric acid participates in more complex reactions. Primarily, it undergoes oxidative decarboxylation to form succinyl-CoA through the enzyme \( \alpha \)-ketoglutarate dehydrogenase.
This reaction produces another molecule of NADH and releases carbon dioxide. Importantly,

• It is a typical example of a highly regulated step in the Kreb's Cycle, ensuring precise control over cell energy levels.
• The compound can cross-link with various metabolic pathways, showing its importance as a precursor for amino acids and neurotransmitters.

Thus, \( \alpha \)-ketoglutaric acid is integral to maintaining cellular balance, making it a versatile molecule in biochemical processes.

Biochemistry

Biochemistry is the science that explores the chemical processes occurring within living organisms. It gives insight into the mechanisms like the Kreb's Cycle that convert nutrients into usable energy and building blocks of macromolecules. Through biochemistry, we understand:

• The transformative pathways like the Kreb's Cycle, providing energy through complex but vital chemical reactions.
• The roles of enzymes and other catalysts in regulating these biochemical processes.
• How molecules like isocitric acid, oxalosuccinic acid, and \( \alpha \)-ketoglutaric acid demonstrate the elegance and efficiency of nature's design.

Understanding biochemistry forms the foundation to grasp how life functions at the molecular level. It helps in fields ranging from medicine, pharmacology to even agriculture, where manipulating biochemical pathways can lead to developments like drug creation or crop improvement. By exploring biochemistry, we appreciate the intricate interplay of life at the smallest scales.