Q68.Restriction enzymes are the enzymes that:

A. catalyze restricted reactions in DNA replication.
B. are essential tools in biotechnology.
C. were discovered by Sanger and Pauling.
D. Cut DNA specifically.
E. are the immune defense mechanism in bacteria.

Choose the correct answer from the options given below:

(1) B, D, E Only
(2) C, D, E Only
(3) A, B Only
(4) C, D Only

Restriction enzymes cut DNA at specific sequences and serve as bacterial defense while being biotech tools. The correct answer is option (1): B, D, E only.

Statement Analysis

A. Catalyze restricted reactions in DNA replication. Incorrect—”restricted reactions” is meaningless terminology; restriction enzymes cleave foreign DNA, not participate in replication.

B. Are essential tools in biotechnology. Correct—Type II enzymes (EcoRI, HindIII) enable cloning, RFLP, CRISPR engineering via precise DNA cutting.

C. Were discovered by Sanger and Pauling. Incorrect—Arber (1965), Smith, Nathans (1970s) discovered; Sanger sequenced DNA, Pauling studied sickle cell.

D. Cut DNA specifically. Correct—recognize 4-8 bp palindromic sequences (GAATTC for EcoRI), producing sticky/blunt ends.

E. Are the immune defense mechanism in bacteria. Correct—Type II/III systems cleave unmethylated phage DNA; host DNA methylated for protection.

Option Breakdown

• (1) B, D, E Only: Correct—captures function, utility, natural role.

• (2) C, D, E Only: Wrong—C false discoverers.

• (3) A, B Only: Wrong—A meaningless.

• (4) C, D Only: Wrong—C false.

Restriction enzymes cut DNA specifically at 4-8 bp palindromic sequences, forming the cornerstone of molecular cloning and bacterial immunity.

Key Properties

• Specificity: EcoRI cuts GAATTC → 5′ AATT overhangs.

• Types: II (lab standard), I/III (complex), IV (methylated DNA).

• Mechanism: H-bonds in major groove → Mg²⁺-catalyzed phosphodiester hydrolysis.

Bacterial Role

• R-M systems: Endonuclease + methyltransferase.

• Foreign DNA cleaved; self DNA protected (e.g., GATC methylation blocks EcoRI).

Biotech Revolution

• Cloning: Insert genes via compatible ends + ligase.

• Applications: PCR, sequencing, gene editing.

Exam Focus

CSIR/NEET tests Arber et al. discovery, NOT Sanger/Pauling. B/D/E define core identity.