Difference Between cDNA and Genomic DNA

Main Difference – cDNA vs Genomic DNA

Complementary DNA (cDNA) and genomic DNA are two types of DNA molecules used in the research experiments in molecular biology. Both cDNA and genomic DNA are made up of DNA nucleotides. cDNA is produced by the reverse transcription of the extracted RNA from tissue. The types of RNA used for the reverse transcription can be total RNA, pre-mRNA, RNA, ribosomal RNA, or tRNA. However, genomic DNA can be directly isolated from the cell. The main difference between cDNA and genomic DNA is that cDNA represents the transcriptome of a particular organism whereas genomic DNA represents the genome.

Key Areas Covered

1. What is cDNA
– Definition, Facts, Role
2. What is Genomic DNA
– Definition, Facts, Role
3. What are the Similarities Between cDNA and Genomic DNA
– Outline of Common Features
4. What is the Difference Between cDNA and Genomic DNA
– Comparison of Key Differences

Key Terms: Complementary DNA (cDNA), Genome, Genomic DNA (gDNA), Reverse Transcription, RNA, Transcriptome

What is cDNA

cDNA (complementary DNA) refers to the synthetic DNA whose base sequences are complementary to the DNA. It is produced from the reverse transcription of RNA templates. Total RNA, pre-mRNA, RNA, ribosomal RNA or tRNA can be used for reverse transcription. Reverse transcriptase is the enzyme that catalyzes the reaction of producing cDNA from RNA. The reverse transcription coupled with PCR is shown in figure 1.

Figure 1: Reverse Transcription Coupled with PCR

cDNA is mainly used in cloning eukaryotic genes in the prokaryotic genomes. Exons consist of the coding region of proteins. In eukaryotes, the coding region is interrupted by introns. During transcription, both introns and exons are coded into the pre-mRNA. But during the mRNA processing, the introns are removed from mRNA, producing a mature mRNA by splicing the exons together. The total mRNA of an organism is called the transcriptome. However, prokaryotes lack mRNA processing mechanisms. Thus, mRNA is used to synthesize cDNA that only contains protein coding regions of the genome. This cDNA is used to clone genes into prokaryotes. cDNA is naturally produced in retroviruses during the conversion of the RNA genome into DNA.

What is Genomic DNA

Genomic DNA (gDNA) refers to the total set of chromosomal DNA in the genome. The total set of genes of a particular organism is referred as to its genome. However, not only genes of the genome are active. Most groups of organisms have similar types of genomic DNA within the group. The genome of the organism is passed from the next generation to the other. Generally, genomes are made up of a large number of base pairs. As an example, the human genome consists of around 3 billion base pairs. The chromosomes of the human genome are shown in figure 2.

Figure 2: Chromosomes of the Human Genome

The four types of sequences found in the genomic DNA are protein-coding genes, tandemly repeated genes, repetitive DNA, and spacer DNA. Genomic DNA is used in many experiments in molecular biology. The isolation of genomic DNA is easy when compared to the preparation of cDNA. Genomic DNA can be used as PCR templates, in cloning, sequencing, preparing genomic libraries, DNA fingerprinting, studying gene structures, and detecting mutations/abnormalities.

Similarities Between cDNA and Genomic DNA

cDNA and genomic DNA are two types of DNA molecules used in the research experiments in molecular biology.
Both cDNA and genomic DNA are made up of DNA nucleotides.
Both cDNA and genomic DNA are made up of a sugar-phosphate backbone.
Both cDNA and genomic DNA are double-stranded molecules.
Both cDNA and genomic DNA are composed of exons.

Definition

cDNA: cDNA is the synthetic DNA whose base sequences are complementary to Genomic DNA.

Genomic DNA: Genomic DNA is the total set of chromosomal DNA in the genome.

Represent

cDNA: cDNA represents the transcriptome.

Genomic DNA: DNA represents the genome.

Synthesized/Extracted from

cDNA: cDNA is synthesized from the reverse transcription of different types of RNA.

Genomic DNA: Genomic DNA can be extracted from existing genomes.

Content

cDNA: cDNA consists of exons or coding regions.

Genomic DNA: Genomic DNA consists of coding and non-coding sequences of an organism.

Quantity

cDNA: cDNA contains a few base pairs.

Genomic DNA: Genomic DNA contains a large number of base pairs.

Use

cDNA: cDNA is used to produce cDNA libraries.

Genomic DNA: Genomic DNA can be used to produce genomic libraries.

Conclusion

cDNA and genomic DNA are two types of DNA molecules used in various types of experiments in molecular biology. cDNA is synthesized from RNA, and it only consists of exons. Therefore, it represents the transcriptome of an organism. Genomic DNA can be readily extracted from the nucleus of the cell. It consists of both coding and non-coding regions. It represents the genome of a particular organism. The main difference between cDNA and genomic DNA is the type of DNA present in each type of DNA molecules.

Reference:

1. “CDNA (Complementary DNA).” Human Genes, Available here.
2. “GDNA – Genomic DNA | Advanced Analytical (AATI).” Advanced Analytical Technologies, Inc. (AATI), Available here.
3. “Genomic DNA Isolation and Applications.” Scribd, Available here.

Image Courtesy:

1. “Reverse transcription polymerase chain reaction” By Jpark623 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Human genome to genes” (CC BY 2.0) via Commons Wikimedia