Question

cDNA probes are copied from mRNA molecule with the help of
A. DNA polymerase
B. RNA polymerase
C. Reverse transcriptase
D. Taq polymerase

Answer 1

Hint: Because of the presence of coding sequences, cDNA is generated from an mRNA and used for various purposes.

Complete Answer:
Various enzymes involved in different molecular processes are:
Restriction enzymes are enzymes that make cuts at particular positions within the DNA, known as restriction sites.
1) DNA polymerases are a group of important enzymes that are essential in DNA replication. They are used to make copies of DNA templates and also help in the repair of the synthesized DNA to prevent mutation.
2) Adenosine deaminase aids in the breakdown of adenosine from food and for the turnover of nucleic acid in tissues. In humans, it helps in the development and maintenance of the immune system.
- cDNA, complementary DNA, is synthesized from a single-stranded RNA (mRNA) template. This process is known as reverse transcription and is carried out by the enzyme reverse transcriptase, also known as RNA-dependent DNA polymerase. This enzyme is mostly seen in viruses such as retroviruses.
- Synthesis of cDNA- After purifying the RNA from host cells, it is used as a template for the cDNA synthesis. Oligo-dT primers are used which are the reverse complement of the poly A tail on the 3’ end of the mRNA.
- A perfect mixture of oligo-dT and random hexamer primers increases the chance of getting a full-length cDNA. For the reverse transcription activity, usually, MMLV reverse transcriptase is used because of its reduced RNAse H activity.
- The cDNA synthesis mixture undergoes a series of heating and cooling activity for a few minutes to finally produce a fully synthesized cDNA. It is used for cloning purposes, and specific DNA sequences from the cDNA can be amplified using PCR and used for other experiments. Retroviruses use reverse transcriptase to produce cDNA naturally and then integrate into the host genome, where it makes provirus

Hence, the correct option is C, ‘reverse transcriptase’.

Note: A DNA contains both introns and exons and the cDNA has only exons (coding sequences). cDNA is often used to clone eukaryotic genes in prokaryotes.