Is Coenzyme Molecule: 9 Interesting Facts (Read This First!)

In this article, we get know about 9+ Important Facts regarding ‘Is Coenzyme Molecule?’, along with their origin, characteristics, functions, importance and examples.

An organic component that attaches to the binding sites of specific enzymes is known as a coenzyme and helps catalyze reactions. More precisely, coenzymes can transfer functional groups across enzymes or serve as intermediates carriers of electrons throughout these processes.

For instance, the conversion of pyruvate to ace necessitates the involvement of two essential metabolic enzymes, such as oxidized NAD- nicotinamide adenine dinucleotide and NADH- reduced nicotinamide adenine dinucleotide. Additional coenzymes include lipoic acid, liberated CoA, thiamine pyrophosphate, and flavin adenine dinucleotide.

Let us discuss some facts and try to understand “Is Coenzyme Molecule”

  • How coenzymes are molecules?
  • What type of molecule are coenzymes?
  • Why coenzyme is an organic molecule?
  • Where coenzymes are found?
  • Is a coenzyme a protein molecule?
  • Important coenzymes examples?
  • Can enzymes soluble in water?
  • Why is acetyl coenzyme a an important molecule in cellular respiration?

Key points: Coenzymes

  • Supporting chemicals called coenzymes and cosubstrates enable enzymes to catalyze chemical processes.
  • In order for a coenzyme to work, an enzyme must be present. It does not operate on its own.
  • Coenzymes are tiny, nonprotein molecules, whereas enzymes are proteins. In order for an enzyme to function, coenzymes must contain an atom or group of atoms.
  • S-adenosyl methionine and the B vitamins are examples of coenzymes..

How coenzymes are molecules?

Coenzymes are made of tiny molecules. Although they cannot catalyse processes themselves, they can help enzymes do so. Coenzymes are organic, the non-protein proteins that contain the protein molecules to create active enzymes, according to the technical definition (holoenzyme).

is coenzyme molecule
Several cofactors, including flavin, iron-sulfur centers, and heme, are visible in the succinate dehydrogenase complex from Wikipedia


  • Coenzymes offer reactive groups that are missing from the side chains of the amino acids and are a part of the enzyme’s active site.
  • Metabolite coenzymes can be created from common metabolites and are coenzymes.. Vitamin-derived coenzymes are those that cannot be manufactured and are derived from vitamins.
  • Coenzymes can also be further categorized according to whether or not they are permanently linked to an enzyme. While transferring electrons, and so on, through one enzyme to another, several enzymes turn on and off.
  • Cosubstrates is the name given to this. Cosubstrates are in fact substrates in the reactions since they undergo changes during the process and separate from the active site.
  • A subsequent independent reaction mediated by a different enzyme must recreate the original cosubstrate structure. As a result, cosubstrates are continuously recycled in the cell while actual substrates often go through additional changes.
  • Prosthetic groups refer to coenzymes that remain linked to an enzyme either covalently or noncovalently (via multiple weak interactions). Each catalytic cycle requires prosthetic coenzymes to change back to their initial state.

What type of molecule are coenzymes?

Currently, a coenzyme is a low-molecular-weight molecule that serves as a substrate for a large variety of enzymes and transfers an electron, hydrogen atom, or chemical group between these many enzymes.

Important coenzymes

  • Coenzymes are crucial parts of the numerous metabolic processes that keep life alive at the cellular level.
  • Coenzymes, which are frequently vitamins or vitamin derivatives, are consequently essential for controlling most enzyme activity. In addition to a few of the coenzymes indicated above that are required in the synthesis of the cellular energy molecule adenosine triphosphate, a number of other coenzymes are regarded to be necessary for the survival of all living cells (ATP).
  • Along with other energy coenzymes like adenosine diphosphate (ADP) and adenosine monophosphate, they also contain two additional redox coenzymes, (NADP+) – oxidized nicotinamide adenine dinucleotide phosphate and its reduced counterpart, NADPH..
  • Some coenzymes, such as oxidized glutathione (GSSG) and reduced glutathione, also serve as antioxidants to neutralize reactive oxygen species (ROS) (GSH).

Why coenzyme is an organic molecule?

Nonprotein chemical molecules called coenzymes bind loosely to an enzyme. Many substances, although not all of them, are vitamins or contain vitamins. Adenosine monophosphate is present in a lot of coenzymes (AMP). One of two terms for coenzymes is cosubstrates or prosthetic groups.


Where coenzymes are found?

Coenzymes are mostly made from vitamins and other minor amounts of other organic vital elements. (Note that some scientists only refer to inorganic substances as “cofactors,” but both kinds are included here).

Coenzymes and citric acid cycle

  • The body needs glucose for the production of ATP, which is used to store and transport energy to all of the cells. Glycolysis, an anaerobic process, and the citric acid cycle, an aerobic process, can both be used to digest glucose.
  • Although the production of ATP through glycolysis does not necessitate the addition of oxygen, this mechanism is unable to fully use the ATP present in glucose.
  • In contrast, the citric acid cycle, that requires oxygen input, can generate more ATP molecules than glycolysis and, as a result, can provide more energy to support the numerous metabolic processes necessary to support life.
  • In reality, the citric acid cycle and oxidative phosphorylation work together to produce more >95% of the energy needed by aerobic cells in humans.
  • All cellular metabolic processes revolve on the citric acid cycle, also referred to as the citric acid cycle (CAC)/ Krebs cycle also known as the tricarboxylic acid cycle (TCA). Acetyl-CoA condenses to citrate to start the TCA reaction.
  • The next step is the dehydration of citrate to create cis-Aconitate, which will then be rehydrated to create isocitrate.
  • Isocitrate is transformed into alpha-ketoglutarate in a two-step process that is catalyzed by the enzyme isocitrate dehydrogenase. As a result of these irreversible processes, carbon dioxide and NADH are produced (CO2).
  • After alpha-ketoglutarate is created, it proceeds through an oxidation-reduction reaction to create succinyl-CoA, a molecule with four carbons, while also reducing NAD+ into NADH.
  • In order to create succinate, succinyl-CoA next goes through an energy-saving step in which guanosine diphosphate (GDP) is phosphorylated to guanosine triphosphate (GTP). GTP rapidly transfers its terminal phosphate group to ADP to create a new ATP molecule after it has been produced.
  • Using the enzyme succinate dehydrogenase, fumarate is created by removing two hydrogen molecules from succinate after it has been generated. Fumarate is created, which enables FAD to take up the two hydrogen molecules to form FADH2.
is coenzyme molecule
Citric acid cycle overview from Wikipedia
  • FADH2 can then move on to the electron transport shift, where it causes the synthesis of 2 new ATP molecules. Regarding the citric acid cycle once more, fumarate is hydrated to create L-malate, which is subsequently dehydrogenated to create oxaloacetate.
  • NAD+ is converted to NADH via the same oxidation-reduction cycle that creates oxaloacetate. Three NADH molecules, one FADH2 molecule, one ATP molecule, and two CO2 molecules are all produced by a single citric acid cycle.
  • The generation of these high-energy products is doubled since a single glucose molecule will split into two pyruvate molecules, each of which will go through its own metabolism via the TCA.
  • Additionally, the TCA-produced energy-dense molecules are essential for the subsequent generation of ATP via the electron transport chain.

Is a coenzyme a protein molecule?

Coenzymes are tiny, nonprotein molecules, whereas enzymes are proteins. In order for an enzyme to function, coenzymes must contain an atom or group of atoms. Coenzymes include things like S-adenosyl methionine and the B vitamins.

Categories of enzymes

Molecules known as cofactors bind to an enzyme during chemical processes. All substances that support enzymes are collectively referred to as cofactors. On the other hand, cofactors can be divided into three groupings based on their chemical composition and function:


These are reusable carbon-containing non-protein compounds (organic). They assist in catalysing processes by loosely attaching to an enzyme’s active site. The majority are vitamins, vitamin derivatives, or nucleotide-based compounds.


True cofactors, as opposed to coenzymes, are reusable, non-protein compounds without carbon (inorganic). Cofactors are often metal ions, such as copper, iron, zinc, cobalt, and others, that are loosely bound to the active site of an enzyme. Because most organisms cannot naturally produce metal ions, these must also be added to the diet.

Prosthetic groups

These could be inorganic metal ions, organic vitamins, carbohydrates, or lipids. To help an enzyme catalyze processes, these groups link to it tightly or covalently, unlike coenzymes or cofactors. These groups are frequently utilized during photosynthesis and cellular respiration.

Important examples of coenzymes

Coenzymes include flavin adenine dinucleotide (FAD), nicotineamide adenine dinucleotide (NAD), and nicotineamide adenine dinucleotide phosphate (NADP) (FAD). These three coenzymes participate in hydrogen transport or oxidation. Coenzyme A (CoA), which is involved in the transfer of acyl groups, is another.

Several Coenzyme Examples

Most organisms are unable to spontaneously create sufficient amounts of coenzymes for their needs. Instead, there are two ways to introduce them to an organism:


  • Not all coenzymes are vitamins or produced from vitamins, but many of them are. An organism will not have the coenzymes necessary to catalyse processes if vitamin consumption is too low.
  • The synthesis of coenzymes is aided by water-soluble vitamins, which include vitamin C and all of the B complex vitamins. Two of the most prominent and popular vitamin-derived coenzymes are nicotinamide adenine dinucleotide (NAD) and coenzyme A.
is coenzyme molecule
The nicotinamide adenine dinucleotide’s redox processes from Wikipedia

  • When NAD is converted into its two alternative forms, it serves as one of the most significant coenzymes in a cell. NAD is generated from vitamin B3. NAD+, a low energy coenzyme, is created when NAD loses an electron. NADH is a high-energy coenzyme that is created when NAD gains an electron.
  • NAD+ primarily functions as an electron carrier for redox processes, particularly those related to the citric acid cycle (TAC). TAC produces ATP and other coenzymes. Mitochondria become less functioning and supply less energy for cell operations when an organism lacks NAD+.
  • NADH is created when NAD+ undergoes a redox reaction and acquires electrons. NADH, often known as coenzyme 1, serves a variety of purposes. Because it is essential for so many diverse processes, it is actually regarded as the most important coenzyme in the human body.
  • This coenzyme mainly transports electrons for reactions and turns food into energy. For instance, the electron transport chain can only start when electrons from NADH are delivered.
  • Cells experience energy deficiencies due to a lack of NADH, which leads to widespread tiredness. In addition, this coenzyme is acknowledged as the most potent biological antioxidant for shielding cells from potentially dangerous chemicals.
  • Acetyl-CoA, often known as coenzyme A, is produced naturally from vitamin B5. This coenzyme serves a variety of purposes. It is first in charge of starting fatty acid synthesis within cells.
  • Fatty acids produce the phospholipid bilayer, a component of the cell membrane that is necessary for life. The citric acid cycle, which results in the generation of ATP, is also started by coenzyme A.


Coenzymes that are not vitamins frequently support the chemical transfer of enzymes. They guarantee that an organism performs physiological processes like blood clotting and metabolism. Adenosine, uracil, guanine, and inosine are some examples of the nucleotides that can be used to make these coenzymes.


  • An example of a necessary non-vitamin coenzyme is adenosine triphosphate (ATP). It is actually the coenzyme that is most broadly disseminated throughout the human body. It moves materials and provides the energy required for vital chemical processes and muscle activity.
  • To accomplish this, ATP transports a phosphate and energy to different parts of a cell. The energy is released along with the phosphate. This process is brought on by the electron transport chain.
  • Normal life processes would not be possible without the coenzyme ATP since there wouldn’t be much energy available at the cellular level.

Function of Coenzymes

The essential proteins known as enzymes are in charge of numerous biological reactions in organisms. They cannot even operate on their own, though. They are essential components of all biological systems.

Some important roles of it are as follows:

1.      Energy Production

Coenzymes play a crucial part in energy production, among other things. A vital component of the transport of energy inside the cell is the coenzyme ATP. There are three phosphate groups in ATP’s structure. when the final one is completely removed by a procedure called hydrolysis.

Energy is released. Every time ATP is regenerated, additional phosphate groups are added. That is then detached once more, replenishing cellular energy.

2.      Transferring Groups

Coenzymes also facilitate the transfer of particular atomic groups through one molecule to another. For instance, hydrogen transfer, which is the movement of hydrogen atoms within a cell or organelle. Several processes, including the reproduction of ATP molecules, depend on it.

In particular, the coenzyme NADH is important in this process. When oxidative phosphorylation first begins in a cell. Four hydrogen atoms are transferred by the coenzyme NADH from one mitochondrial component to the next.

3.      Redox Reactions

Coenzymes’ main function also includes aiding in the loss or gain of electrons during redox processes. When an atom or molecule oxidizes, electrons are lost. Reduction happens when a molecule or perhaps an atom gains electrons.

Another effective illustration of redox is oxidative phosphorylation. A demonstration of how coenzymes cooperate is also provided. As a result, coenzyme Q. NADH receives two electrons from the coenzyme. It then changes to NAD+ and goes into an oxidized form as a result of losing electrons.

4.      Antioxidants

Coenzymes can pick up electrons in large numbers. They frequently serve as antioxidants. These free radicals, also known as unbound electrons. Cells can suffer damage from it, including DNA damage and even cell death. Free radicals can be bound by antioxidants.

It stops such cell damage from occurring. CoQ10 is one example of a coenzyme that is even utilized medically. CoQ10 can be helpful to minimize free radical damage while the heart tissue is mending after a cardiac event like a heart attack or heart failure.

Can enzymes soluble in water

Immobilized enzymes can function as water-soluble catalysts in addition to heterogeneous preparations that are insoluble in water. The latter scenario avoids the need for any diffusion restrictions during catalysis. Additionally, water-soluble enzymes catalyse reactions with macromolecular substrates that are hardly water-soluble.

Why is acetyl coenzyme a an important molecule in cellular respiration

An essential metabolic component of cellular respiration is acetyl-CoA. It is created in the second stage of aerobic respiration following glycolysis and transports the acetyl group’s carbon atoms to the TCA cycle where they are oxidized to produce energy.


In the above article, we studied about Coenzymes, whether they are molecules? Types of Coenzymes, origin, functions and structures. Their role in metabolism and respiration.

Ganeshprasad DN

Hi....I am Ganeshprasad DN, completed my Ph.D. in Biochemistry from Mangalore University, I intend to use my knowledge and technical skills to further pursue research in my chosen field. LinkedIn :

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