Laboratory Review ❮ 249
This competence is ensured by treating the cells with calcium or magnesium. Don’t worry
too much about how this competence business really works. Just know that bacteria must be
competent for transformation to occur.
Key Concepts
- DNA works the same for all cells, both eukaryotic and prokaryotic.
- By adding a gene (changing an organism’s genotype), you can change how it looks (its
phenotype).
- Environmental factors can affect gene expression! If lactose is present, E. coli’s lac operon
will turn on.
Investigation 9: Biotechnology: Restriction Enzyme Analysis of DNA
The three activities in this lab all work together to analyze and compare DNA sequences.
For example, after cutting DNA samples from two different people with the same restric-
tion enzymes, you would see that the RFLP patterns produced by gel electrophoresis are
different. Do you have no idea what that last sentence even means? Read on...
Activity 1: Restriction Enzymes
Restriction enzymes are special because they are very picky about their job—they cut DNA
at very specific sequences, called restriction sites. Many restriction sites are a 4- to 10-nucleotide
base pair (bp) palindrome, a sequence that reads the same from either direction. If a restric-
tion enzyme cuts exactly in the center of the restriction site, it will create blunt ends; if it cuts
the backbone in two places, the pieces will have single-stranded overhanging “sticky” ends
with exposed hydrogen bonds. If you cut two different DNA sequences with the same restric-
tion enzyme, and if sticky ends are created, you could use ligase to then glue two sequences
together, even if the DNA was not originally from the same organism! That is called a recom-
binant DNA molecule, and it is the basis of many biotechnological wonders. For example, if
you isolate the human insulin gene with a restriction enzyme, and use that same enzyme to
cut open a bacterial plasmid, you could glue the human gene into the plasmid. That’s how
therapeutic insulin is produced today (thank you, E. coli).
Activity 2: DNA Mapping Using Restriction Enzymes
Say you wanted to identify somebody based on his or her DNA. You hear about it all the
time, but how is it actually done? Using those restriction enzymes we just talked about,
you can cut up a sample of DNA and look at the sizes of the distinct little pieces you have
created (this requires gel electrophoresis—more on that in a bit). Everyone has a unique
pattern of different lengths of DNA fragments. Restriction mapping is a way to create an
organism’s unique genetic “fingerprint.” These unique DNA fragments are called restric-
tion fragment length polymorphisms (RFLPs). But how do you arrange these little pieces
in such a way that you can compare the DNA of two or more people? Once again, read
on...
Activity 3: Gel Electrophoresis
Another important biotechnological tool is gel electrophoresis. Gel electrophoresis is a lab
technique used to separate DNA on the basis of size. When there is an electric current run-
ning from one end of the gel to the other, the fragments of DNA dumped into the wells
KEY IDEA
BIG IDEA 3
Genetics and
Information
Transfer
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