Biology, Eighth Edition (Raven)

Chapter 18: Genomics

cDNA

How can molecular biologists synthesize DNA from RNA? In most cells RNA is synthesized from DNA. The different types of RNA are each used perform specific functions associated with protein synthesis. Placing functional genes from eukaryotes into prokaryotic cells requires creating DNA from mRNA that has had its introns excised. How do molecular biologists accomplish this? The enzyme reverse transcriptase is used. Reverse transcriptase is produced by certain types of viruses. The viruses contain RNA and create DNA that is used to produce more viruses. Reverse transcriptase’s unusual property of creating DNA from RNA has been exploited by biologists to create intron-free eukaryotic DNA for insertion into prokaryotic genomes.

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


1.	In order to clone eukaryotic DNA into prokaryotic cells

		A)	DNA with both exons and introns must be used
		B)	DNA without introns must be added
		C)	RNA with both exons and introns must be used
		D)	exons must be removed from eukaryotic DNA
		E)	introns must be added back to eukaryotic DNA

2.	In the process of cloning eukaryotic DNA into prokaryotic cells, the role of reverse transcriptase is to make

		A)	double-stranded eukaryotic cDNA from mature mRNA
		B)	mature mRNA from precursor mRNA
		C)	bacterial DNA from eukaryotic DNA
		D)	double-stranded DNA with introns added back
		E)	mRNA from DNA

3.	cDNA is

		A)	DNA with both introns and exons that can be cloned into prokaryotes
		B)	DNA with only introns that can be cloned into prokaryotes
		C)	eukaryotic DNA with only exons that can be cloned into prokaryotes
		D)	used to make precursor mRNA

4.	Prokaryotic DNA contains both exons and introns.

		A)	True
		B)	False

5.	RNA polymerase removes exons from precursor RNA.

		A)	True
		B)	False