Difference Between Mitochondrial DNA and Nuclear DNA

Main Difference – Mitochondrial DNA vs Nuclear DNA

Mitochondrial DNA and nuclear DNA contribute to the genetic makeup of the cell. Mitochondrial DNA (mtDNA) is a double-stranded, circular DNA found inside the mitochondria. It encodes proteins and functional RNAs required by mitochondria. But, some proteins, which are encoded by nuclear DNA are imported from the cytosol. Nuclear DNA (nDNA) is composed of several linear chromosomes, which encodes almost all the proteins required by the cell. Mitochondrial DNA is short compared to the nuclear DNA. The main difference between mitochondrial DNA and nuclear DNA is that mitochondrial DNA is encoded for the genetic information required by mitochondria whereas nuclear DNA is encoded for the genetic information required by the entire cell.

This article explains,

1. What is Mitochondrial DNA
      – Definition, Structure and Composition, Function
2. What is Nuclear DNA
     – Definition, Structure and Composition, Function
3. What is the difference between Mitochondrial DNA and Nuclear DNA

What is Mitochondrial DNA

The mitochondrion is involved in the production of cellular energy via oxidative phosphorylation. Inside the mitochondrion, its own genome is found; this is called mitochondrial DNA (mtDNA). The mtDNA is composed of a double-stranded, circular DNA molecule, which is arranged into a single chromosome. A single mitochondrion consists of dozens of mtDNA copies. Mitochondria consists of multiple mtDNA molecules. A single cell may contain more than 100 of mitochondria. Therefore, per cell, more than 1,000 copies of mtDNA can be found. The number of mtDNA copies per cell depends on the number of mtDNA copies per mitochondria as well as the size and the number of mitochondria per cell. It is composed of around 0.25% of the genetic makeup of the cell. The DNA in the mitochondrion is shown in figure 1.

Figure 1: DNA in the Mitochondrion

Thirty-seven genes are found encoded in mtDNA. These genes are encoded for the proteins required by the functions inside mitochondria as well as the required tRNAs and rRNAs by mitochondria, especially for the protein synthesis. Mitochondrial DNA and RNA polymerases are found localized in mitochondria. The polypeptides synthesized inside mitochondria are subunits, which form the multimeric complexes used either in ATP synthesis or electron transport. The mtDNA is replicated independently from nuclear DNA depending on the cell’s requirement for energy.

In yeast, inheritance of mitochondria is biparental. The mtDNA consists of a maternal lineage of inheritance in humans. Little or no cytoplasm is contributed to the zygote by the sperm in mammals. Therefore, in the embryo, almost all the mitochondria are derived from the ovum. In plants, the inheritance of mtDNA is the same as in mammals. Hence, diseases associated with mtDNA is gained by maternal inheritance. The mtDNA is more susceptible to mutations when compared to nuclear DNA. Mis-sense mutations in the mtDNA cause Leber’s hereditary optic neuropathy. Large deletions in mtDNA cause Kearns-Sayre syndrome and chronic progressive external ophthalmoplegia. Circular mtDNA is shown in figure 2.

Figure 2: Mitochondrial DNA

What is Nuclear DNA

The DNA which makes up the cell’s genome is known as nuclear DNA (nDNA). The nDNA is located in the nucleus of a eukaryotic cell. It is composed of 99.75% of the total genetic makeup of a cell. The nDNA or the genome of a eukaryotic cell is organized into several linear chromosomes, which are found tightly packed inside the nucleus. Human bodies consist of 46 individual chromosomes. Sometimes, nDNA exists in several copies. The number of copies of nDNA in the genome is described by the term ploidy. Human somatic cells are diploid, containing two copies of nDNA, which are called homologous chromosomes. Gametes are found haploid in humans.

The size of the human genome is 3.3 billion base pairs. Human nDNA is composed of 20,000 to 25,000 genes, including the genes found in mtDNA. These genes are encoded for almost all the characters exhibited by the organism. They carry information for the growth, development, and reproduction. Genes are expressed into proteins according to the universal genetic code through transcription and translation. The nDNA is only replicated during the S phase of the cell cycle. Organization of nDNA is shown in figure 3.

Figure 3: Nuclear DNA organization

The inheritance of nDNA is biparental. Each of the two copies of the human genome is inherited from one parent, either from mother or father. The nDNA contains huge variations of the traits they exhibit due to the presence of various alleles per a particular gene. Therefore, nDNA is used in paternity testing in order to find out which daughter organism belongs to which parent in humans. On the other hand, inheritance of diseases is also characteristic to the parents. The nDNA is less prone to mutations. Examples of genetic disorders in the human genome are cystic fibrosis, sickle cell anemia, hemochromatosis and Huntington’s disease. Inheritance of both nDNA and mtDNA is shown in figure 4.

Figure 4: Inheritance of nDNA and mtDNA

Difference Between Mitochondrial DNA and Nuclear DNA

Content

Mitochondrial DNA: mtDNA consists of the mitochondrial genome.

Nuclear DNA: nDNA consists of the cell’s genome, including the mitochondrial DNA.

DNA Structure

Mitochondrial DNA: mtDNA is double-stranded and circular.

Nuclear DNA: nDNA is double-stranded and linear.

Number of Chromosomes

Mitochondrial DNA: mtDNA is arranged into a single chromosome.

Nuclear DNA: nDNA is arranged into several chromosomes. For example, human nDNA is arranged into 46 chromosomes.

Composition

Mitochondrial DNA: mtDNA is composed of 0.25% of the cell’s genetic makeup in animal cells.

Nuclear DNA: nDNA is composed of 99.75% of the cell’s genetic makeup in animal cells.

Enclosure

Mitochondrial DNA: mtDNA is not enclosed by the nuclear envelope.

Nuclear DNA: nDNA is enclosed by the nucleus.

Location

Mitochondrial DNA: mtDNA is freely floating in the mitochondrial matrix.

Nuclear DNA: nDNA is found in the nuclear matrix, fixed to the nuclear envelope.

Genome Size

Mitochondrial DNA: The size of the mtDNA is 16,569 base pairs.

Nuclear DNA: The size of the nDNA is 3.3 billion base pairs.

Histone Proteins

Mitochondrial DNA: mtDNA is not packed with histone proteins.

Nuclear DNA: nDNA is tightly packed with histone proteins.

Number of Copies

Mitochondrial DNA: More than 1,000 copies of mtDNA can be found per cell.

Nuclear DNA: The number of copies of nDNA per somatic cell may differ depending on the species. Human somatic cells contain two copies of nDNA.

Number of Genes

Mitochondrial DNA: mtDNA consists of 37 genes, encoding 13 proteins, 22 tRNAs, and 2 rRNAs.

Nuclear DNA: nDNA consists of 20,000-25,000 genes, including three mt genes.

The tRNAs and rRNAs

Mitochondrial DNA: mtDNA encodes each and every tRNA and rRNA required by mitochondria.

Nuclear DNA: nDNA encodes each and every tRNA and rRNA required by the processes in the cytoplasm.

Autonomy

Mitochondrial DNA: mtDNA encodes for most of the proteins, which are required by mitochondria. But, some proteins required by mitochondria are encoded by nDNA. Therefore,  mitochondria are semi-autonomous organelles.

Nuclear DNA: nDNA encodes for every protein, which is required by the cell.

Non-coding Regions

Mitochondrial DNA: mtDNA lacks non-coding DNA regions like introns.

Nuclear DNA: nDNA contains non-coding regions of DNA like introns and untranslated regions.

Genetic Code

Mitochondrial DNA: Most codons in mtDNA do not follow the universal genetic code.

Nuclear DNA: Codons in the nDNA follow the universal genetic code.

Replication

Mitochondrial DNA: mtDNA is replicated independently from nDNA.

Nuclear DNA: nDNA is replicated only during the S-phase of the cell cycle.

Transcription

Mitochondrial DNA: Genes encoded by the mtDNA are polycistronic.

Nuclear DNA: Genes encoded by the nDNA are monocistronic.

Inheritance

Mitochondrial DNA: mtDNA is maternally inherited.

Nuclear DNA: nDNA is inherited equally from both parents.

Recombination

Mitochondrial DNA: mtDNA is inherited from mother to her offspring without changing.

Nuclear DNA: nDNA is arranged through recombination while transferring to the offspring.

Contribution to the Individual’s Fitness

Mitochondrial DNA: mtDNA has a less contribution to the individual’s fitness among the population.

Nuclear DNA: nDNA has a high contribution to the individual’s fitness among the population.

Rate of Mutations

Mitochondrial DNA: The rate of mutations in mtDNA is comparatively high.

Nuclear DNA: The rate of mutations in nDNA is low.

Identification of Individuals

Mitochondrial DNA: The mtDNA can also be used in the identification of individuals.

Nuclear DNA: The nDNA is used to in paternity testing.

Genetic Disorders

Mitochondrial DNA: Leber’s hereditary optic neuropathy, Kearns-Sayre syndrome and chronic progressive external ophthalmoplegia are the examples of the genetic diseases caused by the mutations of mtDNA.

Nuclear DNA: Cystic fibrosis, sickle cell anemia, hemochromatosis and Huntington’s disease are the examples of genetic diseases caused by the mutations in nDNA.

Conclusion

Nuclear DNA, along with the mitochondrial DNA contribute to the genetic makeup of animal cells. Plant cells contain chloroplast DNA as well in their cells. The nDNA consists of the cell’s genome and mtDNA consists of mitochondrial genome. The nDNA contains genes, which encodes for all the traits exhibited by the organism. The mtDNA is also included in the nDNA. The nDNA consists of more than 20,000 genes. The proteins encoded by these genes are responsible for the phenotypic traits of the organism. The mtDNA is encoded for 37 genes along with the tRNAs and rRNAs required by the functions of mitochondria. Hence, the main difference between mitochondrial DNA and nuclear DNA is their contents. 

Reference:
1. Lodish, Harvey. “Organelle DNAs.” Molecular Cell Biology. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 28 Mar. 2017.
2. Cooper, Geoffrey M. “Mitochondria.” The Cell: A Molecular Approach. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 28 Mar. 2017.
3. Brown, Terence A. “The Human Genome.” Genomes. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 28 Mar. 2017.
4. Alberts, Bruce. “The Structure and Function of DNA.” Molecular Biology of the Cell. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 28 Mar. 2017.
5. Stöppler, MD Melissa Conrad. “List of Genetic Diseases: Definitions, Types, & Examples.” MedicineNet. N.p., n.d. Web. 28 Mar. 2017.

Image Courtesy:
1. “Mitochondrial dna lg” By National Human Genome Research Institute – National Institutes of Health. National Human Genome Research Institute. “Talking Glossary of Genetic Terms.” Retrieved November 17, 2016, from  (Public Domain) via Commons Wikimedia
2. “Mitochondrial DNA en” By derivative work: Shanel (talk)Mitochondrial DNA de.svg: translation by Knopfkind; layout by jhc – Mitochondrial DNA de.svg, CC BY-SA 3.0) via Commons Wikimedia
3. “Eukaryote DNA-en” By Eukaryote_DNA.svg: *Difference_DNA_RNA-EN.svg: *Difference_DNA_RNA-DE.svg: Sponk (talk)translation: Sponk (talk)Chromosome.svg: *derivative work: Tryphon (talk)Chromosome-upright.png: Original version: Magnus Manske, this version with upright chromosome: User:Dietzel65Animal_cell_structure_en.svg: LadyofHats (Mariana Ruiz)derivative work: Radio89derivative work: Radio89 – This file was derived fromEukaryote DNA.svg: (CC BY-SA 3.0) via Commons Wikimedia
4. “Mitochondrial DNA versus Nuclear DNA” By University of California Museum of Paleontology (UCMP) and the National Center for Science Education – “Marshalling the Evidence.” Understanding Evolution. University of California Museum of Paleontology. 22 April 2014. . (CC BY-SA 3.0) via Commons Wikimedia