Question

Which of the following is the biological scissor?
(a)Restriction endonuclease
(a)Gyrase
(a)DNA ligase
(a)helicase

Answer 1

Hint: Biologic scissors are named because they bind (cut) DNA to or close particular detection sequences (restriction sites). They function as an important tool for gene alteration and are commonly used in transformation, transfection, etc.

Complete answer:
A restriction enzyme, restriction endonuclease, or restriction enzyme is an enzyme that binds DNA to fragments at or near-unique detection sites within molecules known as restriction sites. Restriction enzymes are one class in the larger endonuclease category of enzymes.
Restriction enzymes are typically categorized into five groups that vary in their structure and whether they break down their DNA substrate at their position of recognition or whether the recognition and cleavage sites are distinct from each other. In order to cut DNA, all restriction enzymes make two incisions, one into each sugar-phosphate backbone (i.e. each strand) of the DNA double helix.

Additional Information: Gyrase: DNA gyrase is an important bacterial enzyme that catalyzes ATP-dependent negative supercoiling. Double-stranded, closed-circular DNA. Gyrase belongs to a class of enzymes known as topoisomerases that are involved in the regulation of topological DNA transitions.
DNA ligase: DNA ligase is an enzyme that can bind two strands of DNA together by forming a bond between the phosphate group of one strand and the deoxyribose group of another. It is used in cells to bind together the Okazaki fragments that are formed on the lagging strand during DNA replication.
Helicase: Helicases are enzymes that bind and can even reshape nucleic acid or nucleic acid-protein complexes. There are helicases of DNA and RNA. During DNA replication, DNA helicases are important because they split double-stranded DNA into single strands, allowing each strand to be copied.
So, the correct answer is ‘restriction endonuclease’.

Note: These enzymes are present in bacteria and archaea and provide a protective mechanism against invasive viruses. Within the prokaryote, the restriction enzymes selectively cut off foreign DNA in a process called restriction digestion; in the meantime, host DNA is protected by a modification enzyme (methyltransferase) that modifies prokaryotic DNA and blocks cleavage. These two processes together form a restriction-modification framework.