Question

cDNA is formed by
A. DNA dependent DNA polymerase
B. RNA dependent DNA polymerase
C. DNA dependent RNA polymerase
D. DNA ligase

Answer 1

Hint: cDNA is also known as complementary DNA. cDNA synthesis is reverse to central Dogma. It is the DNA synthesised using the RNA template mainly the mRNA. cDNA is used in cloning eukaryotic genes in the prokaryotes.

Complete Answer:
To solve this question, we must know about the synthesis of cDNA.
- cDNA is a gDNA which does not contain the noncoding regions. The cDNA do not contain introns or the non-coding regions.
- cDNA is produced by using an enzyme reverse transcriptase from RNA template by the process called reverse transcription. The reverse transcriptase is coded by retrovirus.
- The DNA synthesis is done by DNA polymerase instead of RNA polymerase. This enzyme uses an RNA template to synthesise DNA. SO it is often referred to as RNA dependent DNA polymerase.
- DNA dependent RNA polymerase is an enzyme which is used to make RNA from DNA in the normal transcription.
- DNA ligase- DNA ligase is an enzyme which joins two fragments of DNA by the forming phosphodiester bond.

The correct answer is (B). cDNA is formed by RNA dependent DNA polymerase.

Additional information: Introns and exons are the nucleotide sequence in a gene. Exons are the coding region whereas introns are the non coding sequences. Introns are removed by splicing.

Note: cDNA has greater advantage over genomic DNA as it does not contain introns. The cDNA libraries are more useful in reverse genetics. cDNA library is created using a DNA cloning method.