Table of Contents
The DNA library is composed of DNA fragments that were transformed into vectors that can recognize and identify specific DNA fragments. There are two kinds of libraries: cDNA or genomic libraries.
The genomic DNA libraries contain huge DNA fragments. On the other hand cDNA libraries are made up of reverse-transcribed, cloned mRNA. In the end, they lack DNA sequences that correspond to genomic regions that aren’t expressed like the introns.
cDNA Library (Complementary DNA library)
- CDNA – It’s the DNA copy of a mRNA molecule created by reverse transcriptase. It’s an enzyme that can utilize either DNA or RNA to serve as their templates.
- They are created with mRNA as templates. their base material
- They represent just the genes of the genome that express under certain conditions.
- cDNA is not a gene with introns, so it is able to be expressed in prokaryotic cells.
- Fully sliced mature mRNA do not contain regulatory and intron regions. So non-coding segments are not found in cDNA libraries like in the genomic library.
- Libraries of cDNA are essential for the study of genes, coding regions as well as expression of genes.
- A collection of clones comprising cDNA fragments from an organism is called an cDNA library.
Steps of cDNA Library formation
The construction process involves several stages.
- The extraction of the total mRNA of an individual is the initial step.
- Isolated mRNA is transformed into cDNA strands via the reverse transcription process.
- Reverse transcription is made possible by an enzyme known as reverse transcriptase. It employs a 3′ primer to initiate the synthesis of the initial CDNA strand which is complementary to the template mRNA strand.
- Double stranded cDNA that result is transformed into smaller fragments by restriction endonucleases before being placed into vectors suitable for the task. The recombinant molecules that are constructed are then incorporated to the host organism and then grown in a culture medium to create Clones.
Genomic DNA library
- Genomic DNA refers to the DNA chromosomal that makes up an entity which is representative of the genomic material. They differ from that of mitochondrial DNA, or bacterial plasmid DNA. They are created directly using genomic DNA and constitute the entire genome of an individual
- In their construction the ligases, restriction endonucleases and ligases are essential
- It could also be your DNA from both as well as prokaryotic entities , and also contains introns
- Introns are the main reason why they are not able to express themselves in prokaryotes. Additionally, prokaryotes are deficient in the intron processing machinery.
- The entire gene pool of an organism is known as the genome. However, not just the genes from the genome are in use.
- The majority of groups of organisms share the same types of genomic DNA within their group. The genome of an organism is passed on from the next generation on to the following. In general, genomes consist of an abundance of base pairs.
- The four kinds of sequences in genomic DNA include proteins-coding genes, tandemly repeated genetics, repeating DNA and spacer DNA.
- Genomic DNA is utilized in numerous studies in molecular biology.
- The extraction from genomic DNA can be simple when compared with 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.
Difference Between cDNA and Genomic DNA – cdna vs genomic dna
|Collection of clones having complementary DNA to the mRNA of an entity||Collection of clones having the complete genomic DNA of an entity|
|Represents genes expressed in a particular cell at a given period of time||Represents all genes|
|Smaller compared to genomic DNA library||Vast in comparison to cDNA library|
|Clone contains Coding and non-coding sequences seen on mRNA only, not the complete gene.||Contains Coding and non-coding sequences for introns and exons. Genomic clones can have sequences of the complete gene|
|Reverse transcriptase enzyme is required for their construction.||Ligases and restriction endonucleases required for their construction.|
|The number of recombinants is way lesser in comparison to the genomic DNA library to be screened.||Way greater number of recombinants compared to cDNA library to be screened.|
|mRNA required to start.||DNA required to start.|
|Can be directly expressed in prokaryotic system as it has only coding sequences||Gene expression extracted from the genomic library is challenging in the prokaryotic systems, as they are devoid of a splicing mechanism|
|reverse transcriptase Occurs in the synthesis of the first cDNA strand||Not involved|
|Vectors used: Phagemids, Plasmids, Lambda phage for harbouring smaller fragments due to the absence of introns||Vectors used: Cosmids, plasmids, Lambda phage, YAC, BAC to harbour larger fragments|
|cDNA Library is prepared by using mRNA as template.||Genomic Library is prepared directly from the genomic DNA.|
|cDNA represents the transcriptome.||DNA represents the genome.|
|cDNA is synthesized from the reverse transcription of different types of RNA.||Genomic DNA can be extracted from existing genomes.|
|cDNA contains a few base pairs.||Genomic DNA contains a large number of base pairs.|
Similarities Between cDNA and Genomic DNA
- cDNA or genomic DNA are two forms of DNA molecules utilized for research in molecular biology.
- The two cDNA as well as genomic DNA is composed from DNA nucleotides.
- Each cDNA as well as genomic DNA is both made from a backbone of sugar and phosphate.
- The two cDNA along with genomic DNA, are two-stranded molecules.
- Both genomic DNA and cDNA are made up of exons.
cdna vs genomic dna pdf