An enzyme is a biological protein that acts as a catalyst to speed up chemical reactions in living organisms. It helps convert one substance into another, playing a vital role in digestion, energy production, and many other bodily processes.
A coenzyme is a small, non-protein organic molecule that works together with an enzyme to help it function properly. It often helps transfer atoms or electrons during chemical reactions and is essential for many metabolic activities in the body.
In today’s lesson, we’re learning the essential differences between enzyme and coenzyme—two important components in biochemical reactions. While enzymes are biological catalysts that directly speed up chemical reactions, coenzymes are non-protein organic molecules that assist enzymes in performing their function.
An enzyme is a protein that acts as a catalyst to increase the biochemical reaction rate without altering itself in the process, while a coenzyme is an organic non-protein molecule that is required by an enzyme to perform its catalytic activity. Therefore, these two types of molecules differ in quite a few aspects:
Enzymes are large molecules, while coenzymes are usually small molecules. Enzymes are mainly globular proteins, whereas coenzymes are non-protein molecules. Enzymes are biological catalysts; while coenzymes are helper molecules to the enzymes, which is necessary for the enzyme to execute its catalytic activity. Enzymes’ structure remains unaltered throughout the reaction, whereas coenzymes are chemically changed after the enzymatic reaction.
Understanding how enzymes and coenzymes work together yet differ is fundamental in biology and biochemistry. The table below outlines 10 critical differences between enzymes and coenzymes, helping you grasp their distinct roles in metabolic processes.
10 Key Differences Between Enzyme and Coenzyme
| Enzymes | Coenzymes |
|---|---|
| Enzymes are protein molecules that act as biological catalysts. | Coenzymes are non-protein organic molecules that assist enzymes. |
| Enzymes directly catalyze biochemical reactions. | Coenzymes help enzymes catalyze reactions by transferring chemical groups. |
| Enzymes have an active site where substrates bind. | Coenzymes do not have an active site; they temporarily bind to enzymes. |
| Enzymes can function independently or with cofactors/coenzymes. | Coenzymes cannot function alone; they must work with enzymes. |
| Enzymes are large macromolecules. | Coenzymes are small, organic molecules like vitamins. |
| Enzymes are specific to the reactions they catalyze. | Coenzymes may assist different enzymes in various reactions. |
| Enzymes remain unchanged after the reaction. | Coenzymes may be modified during the reaction and then regenerated. |
| Enzymes are synthesized by the body from amino acids. | Coenzymes are often derived from vitamins like B-complex. |
| Enzyme deficiency can lead to metabolic disorders. | Coenzyme deficiency, often due to poor diet, affects enzyme function. |
| Examples: Amylase, Protease, DNA polymerase. | Examples: NAD⁺, FAD, Coenzyme A. |
Similarities Between Enzyme and Coenzyme
| Aspect | Similarity |
|---|---|
| Biological Catalysis | Both act as catalysts in chemical reactions—enzymes directly catalyze reactions, while coenzymes assist by transferring specific chemical groups or electrons. |
| Essential for Metabolism | Both play crucial roles in metabolic pathways like cellular respiration, citric acid cycle, and nutrient breakdown for energy production. |
| Temporary Association | Coenzymes bind temporarily to enzymes during reactions; this allows catalysis without permanently altering the enzyme structure. |
| Regeneration | Enzymes remain unchanged after reactions and can be reused; coenzymes, though chemically modified, are regenerated for further use. |
| Specificity | Both exhibit specificity—enzymes are specific to substrates; coenzymes are specific to the chemical groups or electrons they carry or transfer. |
What are Enzymes
They are organic substances of a protein nature, produced by cells, whose function is to accelerate or trigger chemical reactions that occur in living organisms. Enzymes have a specific action since they act exclusively by catalyzing a type of chemical reaction. Thanks to enzymes, cells can carry out their reactions at low pressures, moderate temperatures, and changes in alkalinity or acidity (variations in pH). The substrate is the substance on which the enzyme reacts.
Enzymes act by accelerating the rate of a reaction or by making a specific reaction possible. To carry out its action, the enzyme binds to the substrate by absorption, fitting the surfaces of one into the other in a way that could be compared to a key in a lock. This combination creates a reversible enzyme-substrate intermediate complex, which then breaks down to release the products of a reaction, and the enzyme is able to bind to another molecule of the same substrate to begin the action again.
Each type of enzyme catalyzes a specific type of chemical reaction. Therefore, hundreds of different types of enzymes are required in the metabolism of any type of cell. In other words, enzymes exhibit a high degree of specificity, since each one acts exclusively in a specific reaction and on a specific substrate. Urease, for example, only acts on urea. Alcoholic hydrogenases act on alcohols.
Most enzymes are intracellular since they catalyze reactions that occur inside the cell. Some enzymes produced inside cells are released outside the cell to perform their function; digestive enzymes are extracellular enzymes.
What functions do enzymes perform?
- They facilitate and accelerate chemical reactions carried out by living beings, thus enabling biochemical processes within organisms.
- They release the energy stored in substances for the organism to use as needed.
- They break down large molecules into their simpler constituents, thus allowing them to enter or leave the cell through diffusion.
What are Coenzymes
Some enzymes require a non-protein portion to perform their function: if it's a metal cation, it's called a cofactor; if it's an organic molecule, it's called a coenzyme. The protein portion is called an apoenzyme, and the complete enzyme is called a holoenzyme.
Coenzymes are required to transiently transport functional groups during the enzyme-catalyzed reaction. Many are vitamin-derived products, and their attachment to the protein moiety can be covalent or noncovalent. For example, most carboxylases (enzymes that catalyze the incorporation of CO 2 ) require biotin, which is linked by an amide bond to a Lys residue of the enzyme, while thiamine pyrophosphate (derived from the vitamin, or thiamine) is bound by noncovalent interactions.
Many of the oxidoreduction reactions occurring in cells are catalyzed by dehydrogenases that use two coenzymes derived from the niacin molecule: NAD+ and NADP+. The alternation of these compounds between their oxidized and reduced forms allows them to act as electron acceptors or donors depending on the reaction. In the oxidation of a substrate such as malate, two H atoms are lost (which can be considered as 2e - + 2H+ ) as follows: the hydride ion (2e - + 1H+ ) is transferred from the substrate directly to the coenzyme, while the other proton is released into the medium. NAD+ is often used as a coenzyme in the oxidation reactions of catabolic pathways, while NADP+ participates in anabolic reduction reactions.
Mechanisms of action of coenzymes
- The coenzyme binds to an enzyme.
- The enzyme captures its specific substrate.
- The enzyme attacks the substrate, removing some of its atoms.
- The enzyme transfers these atoms from the substrate to the coenzyme.
- The coenzyme accepts these atoms and releases them from the enzyme.
- The coenzyme is not the final acceptor of these atoms, but must release them sooner or later.
- The coenzyme transports these atoms and eventually releases them, thus recovering its ability to accept new atoms.
Main coenzymes
- FAD (flavin-adenine dinucleotide): electron and proton transfer.
- FMN (Flavin mononucleotide): electron and proton transfer.
- NAD + (nicotine adenine dinucleotide): transfer of electrons and protons.
- NADP + (nicotine adenine dinucleotide phosphate): transfer of electrons and protons.
- Coenzyme A: transfer of acetyl groups (for example, in the decarboxylation of pyruvic acid) and acyl groups in general.
- Coenzyme Q: electron transfer in the respiratory chain.
- Coenzyme B12: transfer of methyl or hydrogen groups between molecules.
- TPP (Thiamine pyrophosphate): aldehyde group transfer; part of the pyruvate dehydrogenase complex, among others.
- Vitamin C
- PLP (pyridoxal phosphate): amino group transfer.
- PMP (pyridoxamine phosphate): amino group transfer.
- FH 4 (tetrahydrofolic acid): transfer of formyl, methenyl and methylene groups.
- Biocytin: carbon dioxide transfer.
- Lipoic acid: transfer of hydrogens, acyl and methylamine groups.
