Question

Restriction endonucleases are: [ can be more than one]

Scientists received Nobel Prize in 1978 for discovering restriction endonucleases.

Bacteria keeps their own DNA modified preventing digestion by their own enzyme.

Enzymes found in bacteria that digests DNA.

Each restriction enzyme recognizes a specific DNA sequence.

Bacteria uses their own restriction enzymes for their defense against viral infection.

Which of the following is/are correct for chemical synthesis of oligo DNA? answer can be more than one

Any nucleotide is added on to the 3rd carbon of the deoxyribose.

Requires or uses dNTPs

The DNA strand is extended in 3' ----> 5' direction.

A nucleotide is added on to the 5th carbon of the deoxyribose.

A strand of DNA is extended in 5' ----> 3' direction.

Answer 1

Oligonucleotide synthesis is the process in which the short strech of nucleic acid is synthesised using chemical approach with specific chemical sequences.Selected nucleotides are added to the single stranded molecule and designed according to the requirement for the complimentary template.A complete DNA strand is obtained by DNA polymerase and ligase.

The correct steps are-

Chemical synthesis initiate from 3'------5' direction specificaly for DNA synthesis.

The step 1 deals with the detritylation 5'DMT protecting group from 3' terminal base of the nucleotide to prevent polymerization of the nucleoside.The step results in the depurination thus limits the quantity of oligonucleotide formation.The product formed is 3' terminal mucleoside and free 5'-OH .

2-Coupling-The free 5'-OH terminal nucleoside id linked with the near by nucleoside forming phosphoramidite monomer.As the step continues the dinucleoside with phosphite triester linkage and free diisopropylamino is obtained.

3-Oxidation-Phosphite triester is converted into phosphate triester required for the formation of stable DNA backbone and beta cyanoethyl protecting group.

4-Capping-Accumulation of shortmers are prevented which is necessary for the purification of newly formed oligonucleotide fragment of DNA.The product thus obtained is solid support linked nucleoside with acetylated 5'-OH.

The product obtained at the end is Oligonucleotide terminal with free 3'-OH.The oligonucleotide is heated to remove protecting group.