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Name: _____________________________ Class: __________________ Date: __________________
Manipulating DNA
Reinforcement 9.1
KEY CONCEPT Biotechnology relies on cutting DNA at specific places.
Many indirect methods are used to study and manipulate DNA, and several
different tools are important in many areas of genetics research and
biotechnology. Some examples include sequencing genes, copying (or cloning)
genes, chemically mutating genes, analyzing and organizing genetic information
with computer databases, and transferring genes between organisms. In many of
these research areas, DNA must first be cut so that it can be studied.
Scientists use enzymes that act like molecular “scissors” to cut DNA. These
enzymes, called restriction enzymes, come from various types of bacteria and cut
DNA at specific nucleotide sequences. Each restriction enzyme cuts DNA at a
different nucleotide sequence, which is called a restriction site. As a result,
different restriction enzymes cut the same DNA molecule in different ways and
can produce different numbers of DNA fragments. Some restriction enzymes cut
straight across a DNA molecule, leaving behind “blunt ends.” Other restriction
enzymes make staggered cuts through a DNA molecule, producing “sticky ends.”
After cutting a DNA molecule with restriction enzymes, the next step in genetics
research is often the separation of the DNA fragments by gel electrophoresis. In
gel electrophoresis, an electrical current separates DNA fragments by their sizes.
DNA fragments travel through a gel toward the positively charged pole, but pores
in the gel slow down larger fragments. Smaller fragments travel farther than larger
fragments in the same amount of time. The pattern of DNA fragments that shows
up on the gel, which shows the sizes of DNA fragments between restriction sites,
is called a restriction map.
1. What are restriction enzymes?
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2. How does gel electrophoresis work?
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3. What does a restriction map show?
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Copyright by McDougal Littell, a division of Houghton Mifflin Company
Biology
2
Frontiers of Biotechnology