The key difference between DNA and cDNA is that the DNA contains both exons and introns while the cDNA contains only exons.
DNA and cDNA are two types of nucleic acids that are made up of deoxyribonucleotides. DNA is one of the most important macromolecules of living organisms that makes the genome. The genome contains the overall genetic information of an organism. It constitutes different types of sequences including exons that are coding sequences and introns that are non-coding sequences. On the other hand, cDNA or complementary DNA is another form of DNA that is artificially synthesized from mRNA molecules by the scientists. Since cDNA derives from mRNA templates, it does not contain non-coding sequences or introns.
CONTENTS
1. Overview and Key Difference
2. What is DNA
3. What is cDNA
4. Similarities Between DNA and cDNA
5. Side by Side Comparison – DNA vs cDNA in Tabular Form
6. Summary
What is DNA?
Deoxyribonucleic acid or DNA serves as the genetic material of many living organisms including bacteria. The genetic information resides in the DNA molecules in the form of nucleotide sequences and genes. During the reproduction, parental DNA transmits to the offspring generation via gametes. Structurally, DNA is a macromolecule composed of monomers of deoxyribonucleotides. Deoxyribonucleotide has three components; deoxyribose sugar, a nitrogenous base (adenine, guanine, cytosine and thymine) and a phosphate group. Furthermore, DNA molecules exist as double helix made from two complementary DNA strands linked by hydrogen bonds between complementary nitrogenous bases. Accordingly, there are two hydrogen bonds between adenine and thymine while there are three hydrogen bonds between cytosine and guanine.
Figure 01: DNA
In the DNA helix, phosphate and sugar moieties locate outside of the helix while the bases remain in the interior of the helix. Two strands of DNA run in opposite directions. Furthermore, DNA molecules tightly coil with histone proteins and make a thread like structures called chromosomes in eukaryotes. An important property of DNA is that it is self-replicating, which means it can replicate or make copies of itself. It also has a major role in protein synthesis of living organisms.
What is cDNA?
cDNA stands for complementary DNA. It is a form of DNA synthesized artificially by messenger RNA (mRNA) that serves as a template in the presence of reverse transcriptase enzyme. In most eukaryotes, genomic DNA contains many genes composed of exons and introns. Exons are the coding sequences while introns make the non-coding part of the genome. Generally, during the gene expression, sense DNA sequence transcribes into an mRNA sequence before producing a protein. When making a mature mRNA, a splicing mechanism removes all the intron sequences. Hence, mature mRNA does not contain introns or the non-coding sequences.
Moreover, mRNA of eukaryotic cells can be extracted and purified in order to make cDNA. The enzyme; reverse transcriptase catalyzes the synthesis of cDNA from these purified eukaryotic mRNA. After constructing cDNA from mRNA, they can then be cloned into a bacterial cell in order to make cDNA libraries or can be used to carry out heterologous expression studies.
Figure 02: cDNA
Usually, cDNA has a big value in cloning of eukaryotic genes in prokaryotes. Since prokaryotes do not contain introns, they are unable to excise introns from eukaryotic DNA and make functional mRNA. Therefore, before cloning whole eukaryotic genes into prokaryotes, it is necessary to remove introns and make cDNA from mRNA and clone into prokaryotes.
What are the Similarities Between DNA and cDNA?
- DNA and cDNA are two forms of nucleic acids.
- Both contain deoxyribonucleotide monomers.
- Also, both possess coding sequences of genes.
What is the Difference Between DNA and cDNA?
DNA is a natural form of nucleic acid while cDNA is an artificially constructed form of nucleic acid. Therefore, this is one difference between DNA and cDNA. Moreover, DNA represents the genome of many living organisms. It composes the coding and non-coding sequences. However, when making mRNA, all the intron sequences are excised since they are not important for the formation of proteins. Hence, mRNA sequences do not contain introns. These mRNA sequences act as templates when synthesizing cDNA. Hence, cDNA does not contain introns. Accordingly, DNA contains introns, but cDNA does not contain introns. We can say this as the key difference between DNA and cDNA.
Furthermore, since cDNA contains only exons, cDNAs are much shorter than DNA. DNA contains some introns that span thousands of base pairs. So, this is also a difference between DNA and cDNA. Moreover, DNA naturally occurs as double-stranded helix while cDNA occurs as single-stranded sequences. DNA polymerase is the enzyme that catalyzes DNA synthesis or the replication while reverse transcriptase is the enzyme that catalyzes cDNA synthesis in the lab.
The below infographic on the difference between DNA and cDNA provides more details about these differences.
Summary – DNA vs cDNA
DNA is an important polymer that makes our genome. On the other hand, cDNA is another form of DNA that is important to make cDNA libraries and produce proteins that are hardly express. mRNA is used to make cDNA. Hence, cDNA does not contain introns. But DNA contains introns. Thus, it is the key difference between DNA and cDNA. DNA is useful for constructing genomic DNA libraries while cDNA is useful for constructing cDNA libraries. Since cDNA does not contain introns, cDNA is shorter than DNA. Most importantly, DNA is double-stranded while cDNA is single-stranded. This summarizes the difference between DNA and cDNA.
Reference:
1.“Complementary DNA.” Wikipedia, Wikimedia Foundation, 7 Dec. 2018. Available here
2. “What Is DNA? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health. Available here
Image Courtesy:
1.”Eukaryote DNA-en”By Magnus Manske, Dietzel65, LadyofHats, Radio89 (CC BY-SA 3.0) via Commons Wikimedia
2.”Formation of a cDNA Library”By PhD Dre (CC BY-SA 3.0) via Commons Wikimedia