Biology, Eighth Edition (Raven)

Chapter 18: Genomics

Restriction Endonucleases

What is the cellular function of restriction endonucleases? The animation below tells you that restriction endonucleases are very useful to molecular biologists. They cut DNA at specific locations and can be used to look for genetic diversity, to cut up DNA into smaller pieces, and/or to splice DNA from different sources into one molecule. In cells restriction endonucleases are used to cut up invading DNA from viruses. The restriction sites are ones found in viral DNA. If, when a virus injects DNA in a bacterium, the restriction enzymes cut up the viral DNA then it cannot take over the bacterium and cause it to manufacture more viruses. Restriction endonucleases are a form of protection against viral infections.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Which of the following could NOT be the recognition site of a restriction endonculease?

		A)	GAATTC CTTAAG
		B)	ATCGAT TAGCTA
		C)	CTGCAG GACGTC
		D)	GCTTGC CGAACG
		E)	GGATCC CCTAGG

2.	The single-stranded ends of DNA molecules can be joined together by

		A)	restriction endonucleases.
		B)	DNA ligase.
		C)	DNA polymerase.
		D)	primase.
		E)	helicase.

3.	Human DNA cut with restriction enzyme A can be joined to

		A)	human DNA cut with restriction enzyme B.
		B)	human DNA that is uncut.
		C)	bacterial DNA cut with restriction enzyme A.
		D)	bacterial DNA that is uncut.
		E)	none of the above

4.	The joining of sticky ends involves the formation of phosphodiester bonds.

		A)	True
		B)	False

5.	Restriction enzymes cut only at specific sites and therefore are not useful for genetic engineering.

		A)	True
		B)	False