R
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ESTRICTION
NZYME
ORKSHEET
N
:
AME
Restriction enzymes are important tools for the researcher. Since each DNA molecule is unique, it will
produce unique fragment sizes when cut by a restriction enzyme. These fragments can be used to identify
DNA molecules.
The DNA fragments need to be separated in order to be compared. The fragments are sorted by passing
them through a gel. The gel acts like a screen, allowing small pieces of DNA to pass through more easily
than large pieces, much like sifting rocks out of dirt. Electricity is used to move the DNA through the gel
matrix. Since DNA has a negative charge when it is placed in an electric field, it migrates toward the
positive pole.
FIGURE 1: Gel Electrophoresis sorting fragments of DNA by size
Results after sorting by size
Negative
Negative
Electrode (-)
Electrode (-)
DNA
DNA
Positive
Positive
Electrode (+)
Electrode (+)
The process of sorting DNA fragments by size using a gel and electricity is called gel electrophoresis.
EcoR
Hind
FIGURE 2: DNA Strand with specific
I and
III sites
EcoRI
HindIII
EcoRI
cut site
cut site
cut site
bp - base pairs
2300 bp
4000 bp
3000 bp
5000 bp
R e s t r i c t i o n E n z y m e W o r k s h e e t 2
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