Which Statement Defines A Coenzyme

Coenzymes are essential components of the many metabolic processes that sustain life on the cellular level.

mitochondria Coenzymes are crucial to mitochondrial metabolic processes. Epitome Credit: Explode / Shutterstock.com

What are coenzymes?

A coenzyme is defined as an organic molecule that binds to the active sites of certain enzymes to assist in the catalysis of a reaction. More specifically, coenzymes tin can function as intermediate carriers of electrons during these reactions or be transferred between enzymes as functional groups.

For case, during the conversion of pyruvate to acetyl coenzyme A (CoA), several coenzymes including costless CoA, thiamine pyrophosphate (TPP), lipoic acid (LA), flavin adenine dinucleotide (FAD), two cellular redox enzymes including oxidized nicotinamide adenine dinucleotide (NAD) and reduced nicotinamide adenine dinucleotide (NADH) are required.

Important coenzymes

Coenzymes, which are often vitamins or derivatives of vitamins, therefore play a crucial role in the regulation of nigh enzyme activities. In improver to some of the aforementioned coenzymes that are involved in the generation of the energy molecule adenosine triphosphate (ATP), several other coenzymes are considered to be fundamental to the existence of all living cells.

These include two additional redox coenzymes of oxidized nicotinamide adenine dinucleotide phosphate (NADP⁺) and its reduced counterpart of NADPH, as well equally other energy coenzymes similar adenosine diphosphate (ADP) and adenosine monophosphate (AMP).

Several coenzymes likewise office as antioxidants to eliminate reactive oxygen species (ROS), some of which include oxidized glutathione (GSSG) and reduced glutathione (GSH).

Coenzymes and citric acrid bicycle

Within the trunk, glucose is required for the synthesis of ATP, which functions to store and transfer energy to cells throughout the body. Glucose tin be metabolized through an anaerobic process known every bit glycolysis or an aerobic procedure known equally the citric acid wheel.

The citric acid cycle. Image Credit: VectorMine / Shutterstock.com

Although glycolysis does not require the input of oxygen to produce ATP, this reaction is limited in its ability to harvest a pregnant amount of ATP that is bachelor from glucose. Comparatively, the citric acid cycle, which requires the input of oxygen, can produce more than ATP molecules than glycolysis and therefore supply more energy to back up the many metabolic processes required to sustain life.

In fact, the citric acid cycle, in conjunction with oxidative phosphorylation, is responsible for producing more than 95% of the energy used by aerobic cells in human beings.

As previously mentioned, the citric acid cycle, which is also referred to as the Krebs wheel or the tricarboxylic acrid cycle (TCA), is central to all metabolic processes that occur within the prison cell. TCA begins with the condensation of the coenzyme acetyl-CoA to citrate. Citrate and so undergoes dehydration to produce cis-Aconitate, which is and so rehydrated to form isocitrate.

Catalyzed past the enzyme isocitrate dehydrogenase, isocitrate is converted through a two-stride reaction to a-ketoglutarate. These irreversible reactions consequence in the germination of NADH and carbon dioxide (CO₂). Once a-ketoglutarate is formed, it then undergoes an oxidation-reduction reaction to class a 4-carbon compound known as succinyl-CoA while simultaneously reducing NAD⁺ into NADH.

Succinyl-CoA and then undergoes an energy-conserving reaction to form succinate, during which guanosine diphosphate (GDP) is phosphorylated to guanosine triphosphate (GTP). Once GTP is formed, it readily transfers its terminal phosphate group to ADP in order to course a new ATP molecule.

Afterward succinate has been formed, the enzyme succinate dehydrogenase is used to remove 2 hydrogen molecules from succinate and grade a new molecule known every bit fumarate. The formation of fumarate allows for FAD to have the 2 hydrogen molecules, thus forming FADH₂.

From here, FADH_ii can enter the electron ship change, which results in the germination of ii new ATP molecules. Returning dorsum to the citric acid bicycle, fumarate is hydrated to form Fifty-malate, which then undergoes a dehydrogenation to form oxaloacetate.

The oxidation-reduction reaction that is responsible for the germination of oxaloacetate besides reduces NAD⁺ to NADH. Taken together, a single citric acid cycle, produces three NADH molecules, ane FADH₂ molecule, 1 ATP molecule and two CO₂ molecules. Since a unmarried glucose molecule volition class two pyruvate molecules, both of which will undergo their own metabolism by the TCA, the production of these high-energy products is doubled. Furthermore, the energy-rich molecules produced by TCA are crucial to the downstream production of ATP via the electron ship chain.

Coenzymes and diseases

In addition to the TCA, other metabolic processes involved in programmed cell death, calcium homeostasis, the production of reactive oxygen species (ROS) and oxidative stress all occur within the mitochondria. The dysfunction of coenzymes, every bit well equally any other mitochondrial components, can straight alter a wide range of both anabolic and catabolic pathways that can contribute to the development of diverse illness states.

Several different neurodegenerative diseases including Alzheimer's illness, Parkinson's disease and Huntington'southward disease are associated with altered mitochondrial dynamics. Similarly, alterations in the redox potential of the mitochondria are also involved in numerous cardiovascular diseases including cardiac hypertrophy, myocardial ischemia, reperfusion injury and hypertension.

To date, there is a limited amount of data available to correlate the direct role that coenzymes accept on these diseases; still, their importance in the regulation of enzymes that are known to contribute to certain disease states allow researchers to conclude the inevitable touch that coenzymes too accept on these health conditions.

While this lack of understanding remains, several clinical studies have already found that incorporating certain coenzyme therapies tin better the occurrence of positive outcomes in the treatment of certain cancers and other diseases. As more than research is conducted to further advance the agreement of what molecular roles coenzymes take in sure illness states, researchers are hopeful that these efforts could upshot in the identification of novel therapeutic targets.

Sources

Guarneri, A., van Berkel, W. J. H., & Paul, C. E. (2019). Alternative coenzymes for biocatalysis. Current Opinion in Biotechnology 60; 63-71. doi:10.1016/j.copbio.2019.01.001.
Djukovic, D., Raftery, D., & Gowda, N. (2020). Affiliate 16 – Mass spectrometry and NMR spectroscopy based quantitative metabolomics. Proteomic and Metabolomic Approaches to Biomarker Discovery ii^nd ed; 289-311. doi:x.1016/B978-0-12-818607-7.00016-v.
Thapa, Yard., & Dallmann, Yard. (2020). Role of coenzymes in cancer metabolism. Seminars in Cell & Developmental Biological science 98; 44-53. doi:ten.1016/j.semcdb.2019.05.027.south
Haddad A, Mohiuddin SS. Biochemistry, Citric Acid Bicycle. [Updated 2020 May 23]. In: StatPearls [Internet]. Treasure Isle (FL): StatPearls Publishing; 2020 Jan-. Available from: https://world wide web.ncbi.nlm.nih.gov/books/NBK541072/.