Name: electron carriers in cellular energy
Uploaded: 2025-05-22T09:05:36.000Z
Duration: 1 min 29 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.8

Role of Reduced Coenzymes NADH and FADH&#8322;

Nicotinamide adenine dinucleotide or NAD+ and Flavin adenine dinucleotide or FAD are the two important coenzymes that act as electron carriers in various biochemical reactions.
During an oxidation reaction, these coenzymes absorb electrons and get reduced into NADH and FADH2.
Then during reduction, the reduced coenzymes release the electrons and convert back to their oxidized form.
In eukaryotic cells, glycolysis and the TCA cycle are two major sources of reduced coenzymes.
In the cytosol, glycolysis oxidizes glucose to pyruvate, reducing NAD+ to NADH.
In the mitochondria, the TCA cycle produces three molecules of NADH and one molecule of FADH2.
However, the NADH produced in the cytosol cannot directly enter the mitochondria. Therefore, two carrier pathways&#8212;the malate-aspartate shuttle and the glycerol phosphate shuttle transfer the electrons to NAD+ or FAD present inside the mitochondria.
Finally, the reduced coenzymes donate their electrons to the electron transport chain to generate a proton motive force for ATP production.

role of reduced coenzymes nadh and fadh&#8322;

The energy released from the breakdown of the chemical bonds within nutrients can be stored either through the reduction of electron carriers or in the bonds of adenosine triphosphate (ATP). In living systems, a small class of compounds functions as mobile electron carriers, molecules that bind to and shuttle high-energy electrons between compounds in pathways. The principal electron carriers that will be considered originate from the B vitamin group and are derivatives of nucleotides; they are nicotinamide adenine dinucleotide, nicotine adenine dinucleotide phosphate, and flavin adenine dinucleotide. These compounds can be easily reduced or oxidized.
Nicotinamide adenine dinucleotide (NAD+/NADH) is the most common mobile electron carrier used in catabolism. NAD+ is the oxidized form of the molecule; NADH is the reduced form of the molecule. Nicotine adenine dinucleotide phosphate (NADP+), the oxidized form of an NAD+ variant that contains an extra phosphate group, is another important electron carrier; it forms NADPH when reduced. The oxidized form of flavin adenine dinucleotide is FAD, and its reduced form is FADH2. Both NAD+/NADH and FAD/FADH2 are extensively used in energy extraction from sugars during catabolism in chemoheterotrophs, whereas NADP+/NADPH plays an important role in anabolic reactions and photosynthesis. Collectively, FADH2, NADH, and NADPH are often referred to as having reducing power due to their ability to donate electrons to various chemical reactions.
This text is adapted from <a href="https://openstax.org/books/microbiology/pages/8-1-energy-matter-and-enzymes">Openstax, Microbiology, Section 8.1: </a><a href="https://openstax.org/books/microbiology/pages/8-1-energy-matter-and-enzymes">Energy, Matter and Enzymes</a>

The energy released from the breakdown of the chemical bonds within nutrients can be stored either through the reduction of electron carriers or in the ...

Education

JoVE Core

Cell Biology

Unit 1

Introduction to Metabolism

KEY TERMS AND CONCEPTS

electron carriers in cellular energy

Electron carriers help store and move energy during nutrient breakdown. Cells can save released energy by reducing these carriers or by making ATP, the cell’s main energy molecule. These mobile electron carriers bind high-energy electrons and shuttle them between compounds in metabolic pathways.

The main carriers discussed here come from the B vitamin group and are nucleotide derivatives. They include nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and flavin adenine dinucleotide. These compounds can switch easily between oxidized and reduced forms.

NAD+ is the oxidized form of nicotinamide adenine dinucleotide, and NADH is its reduced form. NAD+ is the most common mobile electron carrier used in catabolism, the breakdown of molecules for energy. NADP+ is a related carrier with an extra phosphate group, and its reduced form is NADPH. FAD is the oxidized form of flavin adenine dinucleotide, and FADH2 is its reduced form.

NAD+/NADH and FAD/FADH2 are used widely in energy extraction from sugars during catabolism in chemoheterotrophs. NADP+/NADPH has a different main role. It is important in anabolic reactions and in photosynthesis. FADH2, NADH, and NADPH are often called reducing power because they can donate electrons to other chemical reactions.

Electron Carriers in Cellular Energy

overview of metabolism

Metabolism in Plants, Animals, and Microbes

Metabolism is the set of chemical reactions that keep living cells working. These reactions are linked through many pathways. Together, they support the normal function of cells in plants, animals, and microbes. In plants, sunlight is the main energy source. Chlorophyll pigments in the leaves absorb this light. The plant then uses that energy for photosynthesis. During photosynthesis, water is oxidized to oxygen and carbon dioxide is reduced to glucose. Glucose then serves as a starting...

carbohydrate metabolism

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The pay-off phase of glycolysis turns the two three-carbon sugar molecules into ATP, NADH, and pyruvate. By this stage, the cell has already spent two ATP molecules. The remaining reactions recover that investment and add two more ATP molecules and two high-energy NADH molecules. The sixth step oxidizes glyceraldehyde 3-phosphate, a three-carbon sugar made earlier in glycolysis. High-energy electrons are transferred to NAD+, which becomes NADH. A second phosphate group is then added to form...

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Pyruvate is a key product of glycolysis and can follow different pathways depending on oxygen availability. During glycolysis, glucose is oxidized to pyruvate, NAD+ is reduced to NADH, and two ATP are made by substrate-level phosphorylation. In aerobic organisms, pyruvate then enters the citric acid cycle, which helps produce the reduced coenzymes NADH and FADH2. These coenzymes are later oxidized in the electron transport chain to make ATP and regenerate NAD+ and FAD. When oxygen is absent,...

Electron carriers help store and move energy during nutrient breakdown. Cells can save released energy by reducing these carriers or by making ATP, the cell’s main energy molecule. These mobile electron carriers bind high-energy electrons and shuttle them between compounds in metabolic pathways. The main carriers discussed here come from the B vitamin group and are nucleotide derivatives. They include nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and flavin...

overview of nitrogen metabolism

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Nitrogen moves through soil, plants, animals, and microbes in a cycle that keeps this macronutrient available for life. It is a major part of proteins and nucleic acids, so cells need it to build both amino acids and nucleotides. In nature, nitrogen is recycled from organic compounds and stored in several forms, including ammonia, ammonium ions, nitrate, nitrite, and nitrogen gas. Many of the key steps in this cycle are carried out only by prokaryotes. The largest nitrogen pool in terrestrial...

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sugars as energy storage molecules

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Glucose storage in plants and animals helps cells manage energy for metabolism. Sugar is a simple carbohydrate, and cells use it because a lot of energy is stored in its bonds. Consumed carbohydrates often come from photosynthesizing organisms, especially plants. Plants make glucose during photosynthesis by using sunlight to convert carbon dioxide into sugar molecules. Because this builds a larger, energy-storing molecule, the process needs an energy input. Glucose can then be stored for later...

fats as energy storage molecules

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regulation of metabolism

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Cells control metabolic enzymes to match changing needs and conditions. Different cells use different enzymes and energy levels, and those needs can also change within the same cell over time. Stomach cells, fat storage cells, skin cells, blood cells, and nerve cells do not all need the same metabolic activity. A digestive cell also works harder soon after a meal than it does many hours later. As cell needs change, the amount and activity of enzymes change too. Enzymes lower activation energy,...

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Homeostasis keeps body conditions in a steady range through feedback control. Animal organs and organ systems constantly adjust to internal and external changes. This balance is called a dynamic equilibrium because the body keeps adapting while still staying within specific ranges. The goal of homeostasis is to stay near a set point, which is the value the body tries to maintain. A change in the internal or external environment is a stimulus. A receptor detects that change and sends a signal...

key terms and concepts

Learn how NADH, FADH2, and NADPH carry electrons, store energy, and support catabolism, anabolism, and photosynthesis in cells.

Electron Carriers in Cellular Energy | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

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SC.912.L.18.5

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SC.912.L.18.6

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SC.912.L.18.7

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A. All living things are composed of four basic categories of macromolecules and share the same basic needs for life.

B. Living organisms acquire the energy they need for life processes through various metabolic pathways (primarily photosynthesis and cellular respiration).

C. Chemical reactions in living things follow basic rules of chemistry and are usually regulated by enzymes.

D. The unique chemical properties of carbon and water make life on Earth possible.

Electron Carriers in Cellular Energy

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