Citric Acid Cycle
Citric Acid Cycle - Related Videos
02:36
The Citric Acid Cycle
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2019
The citric acid cycle, also known as the Krebs cycle or TCA cycle, consists of several energy-generating reactions that yield one ATP molecule, three NADH molecules, one FADH2 molecule, and two CO2 molecules. Acetyl CoA is the point-of-entry into the citric acid cycle, which occurs in the inner membrane (i.e., matrix) of mitochondria in eukaryotic cells or the cytoplasm of prokaryotic cells. Prior to the citric acid cycle, pyruvate oxidation produced two acetyl CoA molecules per glucose...
00:53
Products of the Citric Acid Cycle
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2025
The cells of most organisms—including plants and animals—obtain usable energy through aerobic respiration, the oxygen-requiring version of cellular respiration. Aerobic respiration consists of four major stages: glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation. The third major stage, the citric acid cycle, is also known as the Krebs cycle or tricarboxylic acid (TCA) cycle. For every glucose molecule that undergoes cellular respiration, the citric acid cycle...
01:37
The Citric Acid Cycle: Overview
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2023
In aerobic organisms, the citric acid cycle is the second stage of cellular respiration wherein molecules derived from the breakdown of carbohydrates, proteins, and fats are oxidized into carbon dioxide and energy. This process is also known as the tricarboxylic acid (TCA) cycle as the first product of the cycle, citric acid, contains three carboxyl groups in its structure. Alternatively, this cycle is also referred to as the Krebs cycle, in honor of its discoverer Sir Hans Krebs. The citric...
01:28
The Citric Acid Cycle: Output
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2025
The citric acid cycle is termed an amphibolic pathway as it operates both anabolically and catabolically. The cyclic reactions balance the flux of the substrates to provide an optimal concentration of NADH and ATP to the cell. Regulation of Citric Acid Cycle The citric acid cycle is regulated in several ways, including feedback inhibition, regulation of enzyme activities, and associated anaplerotic or cataplerotic pathways. The primary substrate of the TCA cycle—acetyl CoA—is produced by the...
05:43
Establishment of a Mouse Model with Cough Hypersensitivity via Inhalation of Citric Acid
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2025
This protocol describes the development of a mouse model with cough hypersensitivity, which can serve as an ideal model for studying the mechanisms of chronic cough.
FAQs
Oxaloacetate functions as the molecule that accepts acetyl-CoA at the beginning of the cycle and is restored by the final reactions. Its regeneration allows another acetyl-CoA molecule to enter, so the pathway can continue processing carbon fuels rather than consuming its initiating component. This recurring arrangement supports sustained energy capture and carbon flow through cellular respiration.
The cycle captures energy in several chemically distinct forms. NADH and FADH2 carry high-energy electrons to the electron transport chain, where they support oxidative phosphorylation. GTP is a directly captured energy-containing product. Considering these outputs separately helps explain how one pathway contributes both reducing power for later ATP production and an immediate nucleotide-based energy source.
Its position at the intersection of major fuel pathways allows carbon from carbohydrates, lipids, and amino acids to enter shared metabolic processing through acetyl-CoA or related cycle intermediates. The pathway therefore does more than support respiration: it coordinates how different fuel sources contribute to energy production and supplies intermediates needed for biosynthetic activity.
For eukaryotic cells, the mitochondrial matrix provides the cellular location in which the cycle’s enzyme-catalyzed reactions occur. Linking this location to the electron transport chain is important because the reduced carriers produced in the matrix must deliver electrons onward for oxidative phosphorylation. This spatial relationship helps connect carbon oxidation with downstream ATP production.
A conceptual analysis follows acetyl-CoA entering the pathway, carbon dioxide being released, and energy being captured as NADH, FADH2, and GTP. It then considers how the reduced carriers transfer electrons to the electron transport chain. This workflow clarifies why carbon oxidation in the cycle contributes to, but does not itself complete, cellular ATP production.
Because the pathway links fuel oxidation, electron delivery, energy production, and biosynthetic intermediates, changes affecting it can be examined as disruptions of broader cellular energy balance. In biology research, studying its carbon dioxide release, energy-carrying products, and connection to oxidative phosphorylation helps frame how altered metabolism may influence cellular function and disease mechanisms.