Main Difference – DNA vs mRNA

DNA and mRNA are the two types of most abundant nucleic acids in the cells. Both DNA and mRNA are made up of nucleotides. DNA is the genetic material of both prokaryotes and eukaryotes. It is self-replicative and a new DNA is produced during DNA replication. A gene is a region (locus) or a specific nucleotide sequence on the DNA strand. mRNA is produced by the transcription of these genes. It contains information of an amino acid sequence of a functional protein. DNA comprises a complex, double-helix structure whereas mRNA is a mostly a single-stranded molecule. The main difference between DNA and mRNA is that DNA is the major biomolecule that is responsible for the continuity of life whereas mRNA is responsible for the protein synthesis.

Key Areas Covered

1. What is DNA
      – Definition, Structure, Function
2. What is mRNA
      – Definition, Structure, Function
3. What are the Similarities Between DNA and mRNA
      – Outline of Common Features
4. What is the Difference Between DNA and mRNA
      – Comparison of Key Differences

Key Terms: Amino Acid Sequence, DNA, DNA Replication, mRNA, Protein Synthesis, Transcription, Translation

What is DNA

DNA (deoxyribonucleic acid) refers to a self-replicative molecule, present in all living organisms, carrying the genetic information. Therefore, DNA is the genetic material of both prokaryotes and eukaryotes. In prokaryotes, DNA is found in the nucleoid of the cytoplasm. A small amount of DNA occurs as plasmids. However, in eukaryotes, DNA is inside the nucleus. Eukaryotic organelles such as mitochondria and chloroplasts also contain some DNA. Adenine (A), guanine (G), cytosine (C), and thymine (T) are the four DNA nucleotides, which serve as the building blocks of DNA. Deoxyribose is the sugar found in DNA nucleotides. DNA in a eukaryotic cell is shown in figure 1.

Figure 1: DNA

The total DNA of an organism is called the genome of that organism. The human genome contains 3 billion nucleotides. These nucleotides are arranged in two strands that are complementary to each other. The adenine bases of one strand form hydrogen bonds with the thymine bases of the other strand. Likewise, the cytosine bases form hydrogen bonds with the guanine bases. This process is called complementary base pairing, and this forms a double-stranded structure of DNA. The DNA double strand forms a double-helix structure. The DNA double helices are arranged in chromosomes and are tightly packed inside the nucleus. DNA molecules are capable of self-replicating to make new copies of DNA from the existing copies. 

What is mRNA

The mRNA (messenger RNA) refers to a subtype of RNA, which is created by transcription and determines the amino acid sequence of a protein. Therefore, it is a transcript of a gene. In eukaryotes, mRNA is produced inside the nucleus and is transported to the cytoplasm. The enzyme responsible for the synthesis of mRNA during transcription is RNA polymerase. The mRNA molecule is made up of RNA nucleotides. Adenine (A), guanine (G), cytosine (C), and uracil (U) are the four RNA nucleotides found in a mRNA molecule. The newly-synthesized mRNA is called the pre-mRNA, which undergoes post-transcriptional modifications to produce a mature mRNA molecule. It includes 5′ cap addition, editing, and polyadenylation. The structure of a mature mRNA molecule is shown in figure 2.

Figure 2: Mature mRNA

 A 7-methylguanosine cap is added to the front of the 5′ end. During mRNA editing, some nucleotides can be changed. A poly (A) tail, which contains around 250 adenosine residues is added at the 3′ end of the mRNA molecule to protect it from degradation by exonucleases. On the other hand, eukaryotic pre-mRNA is composed of both introns and exons. Alternative splicing is another process by which different combinations of exons are spliced together to achieve several types of proteins from a single pre-mRNA molecule. Prokaryotic mRNA is capable of producing a single type of protein after translation. The function of a mRNA molecule is shown in figure 3.

Figure 3: Role of mRNA in the Cell

 Mature mRNA molecules are exported through nuclear pore to the cytoplasm. The mature mRNA is translated into an amino acid sequence of a particular protein in a process called translation. Translation is facilitated by ribosomes in the cytoplasm. The transcription of a DNA sequence into a mRNA molecule and the translation of a mRNA molecule into a protein are called the central dogma of molecular biology. The coding region of each mRNA molecule is composed of codons, which are three nucleotides representing a particular amino acid of the polypeptide chain.

Similarities Between DNA and mRNA

• Both DNA and mRNA are made up of nucleotides.
• DNA and mRNA are the most abundant nucleic acids in a cell.
• Both DNA and mRNA are involved in the production of a functional protein.
• Both DNA and mRNA shows complementary base pairing.

Difference Between DNA and mRNA

Definition

DNA: DNA is a self-replicative molecule present in all living organisms, carrying the genetic information.

mRNA: mRNA is a subtype of RNA, which is created by transcription and determines the amino acid sequence of a protein.

Name

DNA: DNA refers to deoxyribonucleic acid.

mRNA: The mRNA refers to messenger RNA.

Nucleotides

DNA: DNA is made up of DNA nucleotides; adenine (A), guanine (G), cytosine (C), and thymine (T).

mRNA: The mRNA is made up of RNA nucleotides; adenine (A), guanine (G), cytosine (C), and uracil (U).

Sugar

DNA: DNA contains deoxyribose sugars.

mRNA: mRNA contains ribose sugars.

Synthesis

DNA: DNA is synthesized during the DNA replication.

mRNA: mRNA is synthesized by transcription of a gene.

Enzymes Involved in the Synthesis

DNA: DNA polymerase is involved in the synthesis of DNA.

mRNA: RNA polymerase is involved in the synthesis of mRNA.

Location

DNA: DNA is inside the nucleus in eukaryotes and in the cytoplasm of prokaryotes.

mRNA: mRNA is produced inside the nucleus and is transported into the cytoplasm in eukaryotes.

Number of Strands

DNA: DNA is a double-stranded molecule.

mRNA: mRNA is a single-stranded molecule. 

Structure

DNA: DNA is a double-helix.

mRNA: mRNA can be found in stem loop structure.

Molecular Weight

DNA: DNA is a large molecule with comparatively high molecular weight.

mRNA: mRNA is a smaller molecule compared to DNA.

Function

DNA: DNA stores the genetic information of an organism.

mRNA: mRNA carries instruction about the amino acid sequence of a protein.

Ultraviolet Damage

DNA: DNA is more prone to damage by UV.

mRNA: mRNA is more resistant to UV.

Conclusion

DNA and mRNA are the most abundant nucleic acids in the cell. DNA is made up of DNA nucleotides whereas mRNA is made up of RNA nucleotides. DNA is a double-stranded molecule, which serves as the genetic material of a cell. mRNA is a single-stranded molecule, which carries the information of the amino acid sequence of a protein. The main difference between DNA and mRNA is the structure and function of each type of molecule in the cell.

Reference:

1. “What is DNA? – Genetics Home Reference.” U.S. National Library of Medicine, National Institutes of Health, Available here.
2. “Messenger RNA (MRNA).” Encyclopædia Britannica, Encyclopædia Britannica, inc., 1 Apr. 2016, Available here.

Image Courtesy:

 1. “Eukaryote DNA-en” Derived from  “Difference_DNA_RNA-EN.svg“, “Chromosome-upright.png”, “Animal_cell_structure_en.svg“ (CC BY-SA 3.0) via Commons Wikimedia 
2. “Mature mRNA” (CC BY-SA 3.0) via Commons Wikimedia
3. “MRNA-interaction” By The original uploader was Sverdrup at English Wikipedia (Public Domain) via Commons Wikimedia

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