Krebs Cycle

Definition

The Krebs Cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) 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. This cycle plays a crucial role in cellular respiration, connecting to various metabolic pathways and ultimately leading to the production of ATP and electron carriers that feed into the electron transport chain.

5 Must Know Facts For Your Next Test

1. The Krebs Cycle occurs in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotic cells.
2. For each turn of the Krebs Cycle, three NADH, one FADH2, and one GTP (or ATP) are produced, which are essential for energy generation.
3. The cycle is named after Hans Krebs, who first described it in 1937, highlighting its importance in biochemistry.
4. Intermediates of the Krebs Cycle serve as precursors for biosynthetic pathways, linking metabolism to the synthesis of amino acids and nucleotides.
5. The regulation of the Krebs Cycle is influenced by energy levels within the cell, with high levels of ATP inhibiting key enzymes to prevent overproduction.

Review Questions

• How does the Krebs Cycle integrate with other metabolic pathways within a cell?
  • The Krebs Cycle serves as a central hub in cellular metabolism by integrating various substrates from carbohydrates, fats, and proteins into a unified pathway. Acetyl-CoA enters the cycle regardless of its origin, allowing for versatile energy production. Additionally, intermediates produced in the cycle can be siphoned off for biosynthesis, linking energy production with the synthesis of essential biomolecules such as amino acids and nucleotides.
• Discuss the significance of NADH and FADH2 produced in the Krebs Cycle in relation to oxidative phosphorylation.
  • NADH and FADH2 generated during the Krebs Cycle are crucial for oxidative phosphorylation as they act as electron carriers that transport high-energy electrons to the electron transport chain. In this process, NADH donates electrons at complex I while FADH2 donates at complex II. This transfer of electrons drives protons across the mitochondrial membrane, creating a proton gradient that is ultimately used by ATP synthase to produce ATP through chemiosmosis.
• Evaluate how disruptions in the Krebs Cycle can affect overall cellular metabolism and energy production.
  • Disruptions in the Krebs Cycle can lead to severe consequences for cellular metabolism and energy production. If any enzymes in the cycle are inhibited or dysfunctional, it can cause a backlog of substrates and a decrease in ATP production due to reduced flow through subsequent pathways like oxidative phosphorylation. Furthermore, a shortage of NADH and FADH2 would impair electron transport, leading to lower energy availability for cellular processes. These disruptions can also impact biosynthetic pathways that rely on intermediates from the cycle, resulting in broader metabolic imbalances.

Related terms

Acetyl-CoA: A central molecule in metabolism, acetyl-CoA is derived from carbohydrates, fats, and proteins and is essential for entering the Krebs Cycle.

NADH:

A key electron carrier generated during the Krebs Cycle, NADH plays a vital role in transporting electrons to the electron transport chain for ATP production.

GTP: Guanosine triphosphate (GTP) is produced during certain steps of the Krebs Cycle and serves as an energy source similar to ATP.