Functions and Origin of Mitochondrial DNA
- Juliana Eljach
- Jun 2
- 8 min read
When analyzing the human genome, one considers the DNA sequence present in the 23 pairs of chromosomes located in the nucleus of each diploid cell (Sánchez Amador, 2020). This information is fundamental, as it defines both the species and each individual. Moreover, it is remarkable that the human body harbors 300 times more microbial genes than its own DNA, which can be explained by the presence of approximately 100 times more microorganisms than human cells—i.e., around 100 trillion bacteria that live in and on the body. On the other hand, according to Sánchez Amador (2020), a small portion of DNA in cells does not belong entirely to the nuclear genome; this is mitochondrial DNA, a small, double-stranded genetic material that functions independently.
Mitochondrial and Nuclear DNA
Mitochondrial DNA is defined as the genetic material present in mitochondria (Sánchez Amador, 2020). It is considered the mitochondrion’s own chromosome because it resides outside the nucleus and consists of a small, circular double strand with a simplified organization compared to the complex arrangement of nuclear DNA. To highlight the differences between the two, one notes that the mitochondrial genome contains 37 genes, whereas nuclear DNA comprises between 20,000 and 25,000 genes; likewise, the former spans approximately 16,500 base pairs compared to the 3.2 billion base pairs of the latter. In addition, the circular double strand of mitochondrial DNA encodes proteins that are exclusive to the organelle, whereas nuclear DNA performs multiple functions within the cell. According to Sánchez Amador (2020), these differences demonstrate that, despite sharing the basic nucleotide structure, each type of DNA exhibits distinct characteristics and functions, revealing a clear distinction in genetic organization.
Structure of Mitochondrial DNA
First, it should be noted that the mitochondrial genome consists of a circular double-stranded DNA, and each of its strands is given a special designation based on its particular characteristics (Sánchez Amador, 2020). In this regard, the H strand (Heavy) has a higher sedimentation coefficient and contains the coding sequences for 28 of the total 37 genes. Furthermore, according to Sánchez Amador (2020), the mitochondrial genetic information encodes crucial components: two ribosomal RNAs, which form part of the organelle’s ribosomes; 22 transfer RNAs, indispensable for protein synthesis; and 13 structural genes that produce various subunits of the enzymatic complexes of the oxidative phosphorylation system.
It is important to point out that, although mitochondria have their own ribosomes and can synthesize proteins autonomously, the majority of mitochondrial proteins originate from nuclear DNA (Sánchez Amador, 2020). As Sánchez Amador (2020) explains, these proteins are synthesized by cytosolic ribosomes and are subsequently imported into the organelle, demonstrating the interrelationship between the two genetic systems.
Functions of Mitochondrial DNA
Energy Production
One of the primary functions is to generate ATP through the electron transport chain and oxidative phosphorylation (Calvo, 2023). Mitochondria possess the enzymatic machinery that converts the energy of nutrients into ATP, which is the essential fuel for cellular processes. In this context, Calvo (2023) states that mitochondrial DNA encodes proteins that are critical for the proper functioning of the mitochondrial respiratory chain, thereby ensuring efficient energy production.
Regulation of Cellular Metabolism
In addition to energy production, mitochondrial DNA participates in regulating cellular metabolism, influencing the synthesis and degradation of important molecules such as fatty acids and tricarboxylic acid cycle intermediates (Calvo, 2023). According to Calvo (2023), proteins derived from this genetic material are indispensable for maintaining the cell’s metabolic balance.
Response to Cellular Stress
Mitochondrial genetic material is actively involved in the stress response, playing a crucial role in regulating cellular processes that allow adaptation and survival under adverse conditions (Calvo, 2023). During stressful conditions, Calvo (2023) explains, apoptosis mechanisms are activated to eliminate damaged or dysfunctional cells via the release of pro-apoptotic proteins, thus contributing to cellular homeostasis.
Production of Ribosomal RNA and Transfer RNA Synthesis
Mitochondrial genetic material encodes two types of ribosomal RNA—12S and 16S—which are essential components of the mitochondrion’s ribosomes and play a critical role in facilitating protein synthesis (González Mora, 2025). Likewise, González Mora (2025) notes that 22 transfer RNAs are encoded, which are necessary for translating genetic instructions into specific mitochondrial proteins.
Regulation of Mitochondrial Function
According to González Mora (2025), proteins produced from mitochondrial DNA help control electron flow in the respiratory chain, ensuring optimal energy production and regulating the generation of reactive oxygen species (ROS).
Contribution to Cellular Homeostasis
González Mora (2025) further explains that the combination of proteins and RNAs encoded by mitochondrial DNA supports the cell’s energy balance, which is especially critical in tissues with high energy demands, such as muscle, brain, and heart.
Participation in Aging and Stress Response
González Mora (2025) also indicates that mutations or damage to mitochondrial DNA can compromise energy production efficiency, affecting the aging process and the cell’s ability to respond adequately to oxidative stress.
Characteristics of Mitochondrial DNA
Polyplasmia
It is observed that each mitochondrion contains multiple copies of DNA, as this genetic material associates with proteins to form a structure called the “nucleoid” (Sánchez Amador, 2020). Specifically, Sánchez Amador (2020) mentions that up to 10 nucleoids can be found per mitochondrion, which translates to approximately 10,000 copies of mitochondrial DNA per cell.
Maternal Inheritance of Genetic Traits
Mitochondrial DNA is transmitted from the mother to her offspring, ensuring the continuity of essential mitochondrial functions (González Mora, 2025). This genetic material is inherited exclusively via the maternal line because, when the sperm fertilizes the egg, its mitochondria—and the tail—are destroyed upon entering the egg’s cytoplasm. However, some studies suggest that paternal mitochondria may occasionally enter the nucleus and persist in certain tissues, such as muscle, a situation that remains under debate. Additionally, the ease of constructing genealogical trees from mitochondrial DNA has allowed numerous population migration studies to rely on these genes, significantly contributing to reconstructing much of human history. Moreover, González Mora (2025) states that several companies offer services to clarify individuals’ familial connections to their ancestors through techniques that analyze these genetic characteristics.
High Rate of Change
Mitochondrial DNA is located in close proximity to the cellular respiration machinery, exposing it to free radicals generated during that process and, thus, to a higher risk of damage (Sánchez Amador, 2020). Consequently, it has a complex repair system that includes various forms of recombination to counteract this damage. According to Sánchez Amador (2020), mitochondrial DNA exhibits a mutation rate up to ten times higher than that of nuclear DNA, facilitating a much faster evolutionary mechanism compared to other living organisms.
Origin of Mitochondrial DNA
Approximately 2 billion years ago, the mitochondrion originated from a free-living aerobic bacterium that was engulfed by an anaerobic nucleated cell (Sánchez Amador, 2020). This integration occurred via an endocytic process, initiating a symbiotic relationship that, over time, led to the transformation of the ancestral bacterium. Throughout evolution, that bacterium lost most of its genes, which were incorporated into the host cell’s nuclear DNA, allowing mitochondrial DNA to retain characteristics typical of prokaryotic microorganisms. Moreover, this organelle is essential for producing the chemical energy required in biochemical reactions, making its function indispensable for life. Therefore, Sánchez Amador (2020) highlights how astonishing it is that an event as fortuitous as one cell engulfing another would trigger the biological diversity explosion that eventually gave rise, among other species, to humanity.
Mitochondrial Mutations
Mutations in mitochondrial DNA can lead to severe diseases, particularly in organs with high energy demands, such as the brain, muscles, and heart (Alemañ Romero, 2018). In this context, some diseases stand out as paradigmatic examples of these alterations. Leber’s Hereditary Optic Neuropathy (LHON) is characterized by an inherited optic neuropathy that leads to progressive blindness, while MELAS syndrome is defined by mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes. On the other hand, Leigh syndrome is a progressive neurological disorder that affects child development and causes central nervous system degeneration. Additionally, Alemañ Romero (2018) notes that the diagnosis of these conditions is carried out through detailed analyses of mitochondrial DNA, which allow for identifying specific mutations responsible for the pathology.
Mitochondrial Impact
A study conducted by the University of Cambridge revealed that genetic variation in mitochondrial DNA can influence the development of common diseases such as diabetes and is associated with cardiometabolic traits, height, and longevity (Tolosa, 2021). Researchers also found correlations between the genetic structure of nuclear DNA and mitochondrial DNA, which is significant because disease risk has traditionally been attributed primarily to nuclear genome variation. Tolosa (2021) mentions that, unlike nuclear DNA—which comprises approximately 3 billion base pairs—mitochondrial DNA is much smaller, at 16,500 base pairs, and is primarily known for its involvement in the development of mitochondrial diseases inherited through the maternal line.
In a study published in Nature Genetics, researchers at the University of Cambridge developed a protocol to examine mitochondrial genetic variation (Tolosa, 2021). They analyzed 473 variable positions in samples from 358,000 UK volunteers, comparing these data with clinical and biometric information. The results revealed 260 associations between the mitochondrial genome and various traits, including multiple sclerosis, type 2 diabetes, renal and hepatic function–related metabolic characteristics, height, and longevity. According to Tolosa (2021), these findings—which require detailed analysis to confirm their influence and uncover underlying mechanisms—raise questions about how mitochondrial genetic variation affects different traits and why, in some cases, different variants produce similar effects while in others the same variant is associated with opposite effects.
First, mitochondrial DNA encodes protein components essential for energy production (Tolosa, 2021). Thus, genetic variations that affect energy metabolism can have a direct impact on the corresponding tissue. On the other hand, according to Tolosa (2021), given mitochondria’s central role in regulating cellular processes, subtle changes in its genetic material could modulate tissue-specific metabolic pathways.
Another interesting aspect noted by researchers is the potential compatibility between mitochondrial DNA and nuclear DNA, since both must coordinate to produce components of an essential organelle (Tolosa, 2021). In fact, certain mitochondrial DNA profiles reflect nuclear DNA ancestry, suggesting that these genomes may have coevolved. This concept of compatibility implies that some combinations of mitochondrial and nuclear DNA are more efficient and have been selected over evolutionary time. According to Tolosa (2021), this hypothesis—pending further study—could have important implications for mitochondrial transfer therapies aimed at preventing the transmission of diseases caused by mitochondrial DNA mutations.
Importance of Mitochondrial DNA
One of the most relevant features of mitochondrial DNA is its exclusive mode of maternal transmission (Alemañ Romero, 2018). This means that all mitochondrial DNA present in a person comes only from their mother. The reason for this phenomenon lies in fertilization, since the egg provides the mitochondria to the zygote. In contrast, the sperm carries primarily the nuclear genetic information and almost no cytoplasm, so it does not contribute mitochondria during fertilization. Thanks to this mode of inheritance, a mother and her children share identical mitochondrial DNA, making it an extremely effective tool for tracing maternal genetic lines. According to Alemañ Romero (2018), this principle even allows researchers to go back many generations to identify a common maternal ancestor of humanity, known as the “Mitochondrial Eve.”
Today, mitochondrial DNA inheritance is routinely used in specialized genetics laboratories (Alemañ Romero, 2018). Tests based on this type of DNA enable precise determination of maternal or sibling relationships because mitochondria transmit consistent genetic information across maternal generations. Moreover, mitochondria play an essential role in cellular energy production. When mitochondrial DNA is altered and does not function properly, it can cause cellular dysfunction and even cell death. According to Alemañ Romero (2018), mitochondrial diseases tend to affect tissues and organs with high energy demands—such as the brain, heart, liver, skeletal muscles, kidneys, and the endocrine and respiratory systems.
It is estimated that approximately 15 percent of these diseases originate from mitochondrial DNA defects (Alemañ Romero, 2018). According to Alemañ Romero (2018), the remainder are due to mutations in nuclear DNA, which is responsible for regulating the production of proteins essential for proper mitochondrial function.
References
Alemañ Romero, M. (2018). Qué es el ADN Mitocondrial y qué Importancia Tiene. Centro de Fertilidad y Genética. https://cefegen.es/blog/adn-mitocondrial-que-es-importancia/
Calvo, I. (2023). ADN Mitocondrial: Características y Funciones. Mentes Abiertas Psicología; Mentes Abiertas Psicología. https://www.mentesabiertaspsicologia.com/blog-psicologia/adn-mitocondrial-caracteristicas-y-funciones
González Mora, R. (2025, enero 16). ADN Mitocondrial. Lifeder. https://www.lifeder.com/adn-mitocondrial/
Sánchez Amador, S. A. (2020, octubre 16). ADN Mitocondrial: Qué es, y Cuáles son sus Características y Funciones. Psicología y Mente. https://psicologiaymente.com/salud/adn-mitocondrial
Tolosa, A. (2021, junio 16). El ADN Mitocondrial Influye en el Desarrollo de Enfermedades Comunes. Genotipia. https://genotipia.com/genetica_medica_news/adn-mitocondrial-enfermedades/
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